Richard Casten

Zierler:

Okay. This is David Zierler, oral historian for the American Institute of Physics. It is June 25, 2020. It is my great pleasure to be here with Professor Richard Casten. Rick, thank you so much for being with me today.

Casten:

My pleasure. I hope this will be interesting to people.

Zierler:

Absolutely. Okay, so to start, please tell me your title and your institutional affiliation.

Casten:

I’m D. Allan Bromley Professor of Physics Emeritus—that means old—at Yale, and what else did you ask? [Laughing]

Zierler:

Yeah, your title and institutional affiliation.

Casten:

Yeah. I also have a part-time appointment at Michigan State associated with the facility they’re building called FRIB.

Zierler:

What is FRIB?

Casten:

FRIB stands for… Nobody knows what FRIB stands for because we’ve always used FRIB. Facility for Rare Ion Beams. It’s a facility to study nuclei that don't exist normally in nature and which are leading to revisions in all our ideas about atomic nuclei.

Zierler:

Oh, wow. Okay.

Casten:

It’s under construction. It will be finished in about a year, and I have a part-time consulting appointment there.

Zierler:

Why Michigan State? Why was this chosen as the site?

Casten:

Well, there was a competition. In the end, the competition boiled down to Argonne National Lab and Michigan State, and Michigan State won a tough competition. It’s not… That may sound random, but even before that and much more now, they are far and away the best university for low energy nuclear physics in the US, actually in the world. By far and away. And, with their existing cyclotron facility, they are also one of the largest. So it’s a natural place for it to be, and they’re doing an amazing job in constructing it. They’re on budget and ahead of schedule.

Zierler:

All right! That’s good to hear! And I believe there’s one more connection you didn't mention. You're founder and co-president of JoAnn and Richard Casten, Limited.

Casten:

Yes.

Zierler:

What is that?

Casten:

Well, we sell original antique maps dating from 1475 up to about 1750.

Zierler:

Oh!

Casten:

The way we got into that is I did a post-doc in Copenhagen. We lived in a house that was built in the early 1700s, and we thought it would be nice to find some view of the street from those days in one of the antique shops. We didn't; we found a map of Amsterdam from 1573, got interested in old maps, and started trying selling a few to finance buying them. The tail wagged the dog and it became a full-fledged business.

Zierler:

[Chuckles] And it’s still active today.

Casten:

No. We pretty much finished it in the last two years. At one point I think we were the fourth or fifth largest antique map seller in the Western Hemisphere.

Zierler:

Oh, wow!

Casten:

Well, it’s a small niche field. I mean, there are not ten million of them. No, the last three or four years we’ve been phasing it out. We have sold the last map, or next to last map that we want to sell, and we’re auctioning off some reference books. So basically we’re dormant.

Zierler:

Now absent the pandemic, are you local to New Haven? Do you still go into the department?

Casten:

So I have an emeritus position there. I have an office there. Even before the pandemic, I was only there maybe ten days a year. The accelerator facility that they had there and that I was director of no longer exists. Physically it’s not even there; it’s been cut up. They’re doing different kind of physics that’s not my field, so research-wise there’s really no reason to go there, but I go there to maintain some contacts and so on.

Zierler:

And you became emeritus when? In 2015?

Casten:

Yep.

Zierler:

2015. Okay, great. So let’s now take it right back to the beginning. Let’s start with your parents. Where are your parents from, Rick?

Casten:

My parents are… My father is from New York. My mother, I think, was born in New York. She lived a few years in Pittsburgh—basically New York. Let’s say New York. Um…yeah.

Zierler:

What did they do for a living? What were their professions?

Casten:

My father was a doctor, a surgeon. My mother was—what’s the politically correct word?—a homemaker.

Zierler:

She worked inside the home. [Chuckles]

Casten:

Yeah, she worked inside the home. And…yeah.

Zierler:

And where did you grow up?

Casten:

I grew up in Manhattan on East 77th Street. That was in the days when the Third Avenue El—El means elevated…

Zierler:

Yeah.

Casten:

Yeah. Third Avenue El went by my window and…yeah.

Zierler:

What kind of school did you go to? Did you go to public school, private school?

Casten:

I went to a private school called Friends. It’s a Quaker school down on 15th Street and Rutherford Place. I don't think it’s named after that Rutherford. Yeah.

Zierler:

Did your family have a Quaker background, or that was just the best school to attend?

Casten:

I don't know if it was the best, although we thought it was, but… Actually, when I was there I didn't think it was that good, but it turned out to be good. No. In fact, I think there was maybe one Quaker in our entire class. No, it was just a private school.

Zierler:

Mm-hmm [yes]. Mostly Jewish and Catholic kids?

Casten:

Let me think for a minute. No, no, I wouldn't say that. There were a few of each. My class only had 25 people in it.

Zierler:

Oh, that’s small.

Casten:

Yeah. So it made it hard to field a baseball team. 11 boys, 14 girls. No, religiously I would say it’s just a distribution over many religions.

Zierler:

When did you start getting interested in math and science?

Casten:

That’s easy. Up through tenth grade I wanted to be a doctor like my father. Then I took chemistry and I discovered atoms and I thought they were the coolest thing going. Later I realized that they weren't, that the nuclei inside were the coolest things going. So in eleventh grade when I took chemistry, I thought I wanted to be a research chemist. Then when I got to twelfth grade and took physics, I realized that the part of chemistry I liked was the physics, so I decided to become a physicist.

Zierler:

Did Sputnik have a big impact on you?

Casten:

Sputnik was shocking! I mean I remember the day, October 4, 1957. It was a shock, but I don't think it had any effect… I can't remember any effect it had on the field of work.

Zierler:

And when you were thinking about colleges, were you thinking specifically about physics programs?

Casten:

You know, I don't think so. Students today know everything about everywhere they apply, and in those days I don't remember knowing anything. I applied to three schools… My mother was Catholic. My father was Jewish. So here’s a detail. When I was about three years old, my mother had a brain tumor, and she went to a doctor in Baltimore who did an operation, and it was one of the first modern brain surgeries ever. At that point, my father said that if she survived, he’d become a Catholic, so he became a Catholic. [Chuckles]

Zierler:

Wow.

Casten:

So I applied to two Catholic schools, Holy Cross and Georgetown, and also to Columbia. I got into all three and went to Holy Cross.

Zierler:

Why Holy Cross?

Casten:

I didn't want to stay in the city. I went down and visited Georgetown and didn't like it. Went to Holy Cross and liked it, so there you go.

Zierler:

There you go. Did you declare the physics major right away or later on?

Casten:

Yes, from the get-go.

Zierler:

Mm-hmm [yes], mm-hmm [yes]. Was there a general education requirement at Holy Cross, or you were able to mostly focus on math and science?

Casten:

No, exactly the first. Holy Cross actually didn't have a very good physics faculty. There was one guy there who was good. Most of the other faculty in physics were not that great, but the best thing about it—and the reason to this day I’m happy I went there—was I got to take a lot of history courses, philosophy courses, that general kind of general liberal arts. I didn't take many advanced physics courses… Well, I did from the beginning, but a large part of the curriculum was what you’d call liberal arts. I’ve always been fascinated by history and archeology.

Zierler:

So you're glad that you had that broader education.

Casten:

Oh, yeah. It’s actually had an effect on my whole research career.

Zierler:

Really! In what way?

Casten:

Yeah. To this day—how should I say it?—a lot of my research has been looking at… Well, first of all, trying to look at things from a different perspective, thinking out of the box (a 19th century baseball expression), and looking at correlations between different kinds of things, different observables, and kind of taking a broader perspective on things. That comes directly from the kind of stuff I studied at Holy Cross. So in retrospect, I’m very glad.

Zierler:

Did you have any—

Casten:

It didn't prepare me very well in science. When I went to graduate school at Yale… Well, I’ll give you an example. My main professor at Holy Cross, when I told him I was going to Yale, looked at me and said, “Huh. Good luck.” [Laughter]

Zierler:

That was not so much a lack of confidence in you, but at the level of education and preparation you had up to that point.

Casten:

Probably. Anyway, when I went to Yale, I was clearly one of the least prepared. The first year was unbelievably hard.

Zierler:

Yeah, yeah. Well, before we get to Yale—

Casten:

I would get—

Zierler:

Before we get to Yale, I want to stay on Holy Cross for a second. Did you have any physics-related jobs during the summer during your undergraduate days?

Casten:

No, no. I worked one or two summers at a company called…oh my god. It was one of these techno companies. It wasn’t Raytheon, but it was someplace like that. I can't remember the name. The rest of the time I took off. I was in the honors program at Holy Cross, and they had a lot of summer reading that we had to do, so it pretty much occupied the summers.

Zierler:

Rick, I’m curious if over the course of your undergraduate career you had well defined yourself in terms of what kind of physics you wanted to pursue afterwards. Did you know coming out that nuclear physics or atomic physics was the thing for you, and that you wanted to focus on experimentation or theory?

Casten:

I knew completely I wanted to go into nuclear physics. Theory or experiment, I don't really remember. I don't think I had really thought about that, but definitely nuclear. That’s why I made the comment about chemistry that now I don't think atoms are the coolest thing.

Zierler:

Right, right. And so that’s—

Casten:

I consider them as big pains in the neck that we have to get around.

Zierler:

[Laughs] So that interest even as a senior, that stayed with you throughout your undergraduate.

Casten:

Yes, yes, yes.

Zierler:

At what point… Did you go straight to graduate school from Holy Cross?

Casten:

Yes.

Zierler:

At what point did you make that decision that you wanted to stay on that track?

Casten:

I don't think I made the decision. I think it was always what I wanted to do.

Zierler:

Mm-hmm [yes], mm-hmm [yes]. What schools did you apply to for graduate work?

Casten:

God, I didn't know this was going to be that tough. Columbia, Yale… [Sighs] Those are the only two I remember; there must have been others.

Zierler:

Okay. So why Yale at the time?

Casten:

Again I visited Columbia and didn't like it. I mean there’s nothing wrong with it; it just didn't suit me. And Yale had a very good nuclear physics faculty. I can't remember if I knew this or not, but they were in the process of building what was then the best accelerator in the world in nuclear physics, a tandem.

Zierler:

Right.

Casten:

This was in the era when tandems were being built.

Zierler:

What was the promise of tandems? What was exciting about them?

Casten:

Oh, that’s easy, but I’ve got to talk about a little physics for that.

Zierler:

Sure! Please.

Casten:

If you want to study nuclei… Well, let me start off with Chihuahuas. If you want to study a Chihuahua, you don't hit it with a truck. You have to hit it with something comparable in size like another Chihuahua, okay? So if you want to study nuclei, you’ve got to probe them with something roughly the same size. You can think of this either in geometrical size or wavelength. So generally you hit them with another nucleus, okay? Now nuclei—forget the electrons. Nuclei are positively charged, and so there’s a Coulomb force and they repel each other, okay? So if you only have low-energy accelerators, you can only study light nuclei that don't have very many protons. You reach a point around magnesium, let’s say, where you don't have enough energy in the beams to get the nuclei to interact. So in the early days, in the ’50s, very early ’60s, most accelerator nuclear physics was very light nuclei. What tandems brought in was much higher energies. The energies of the beams got up high enough that you could smash much heavier nuclei into much heavier nuclei and march up the nuclear chart. So you could do tin on tin, lead on zirconium, things like that, and it opened up the whole field tremendously. I would make a bet. I haven't done this, but I would make a bet that if you categorized the number of papers, say experimental papers on nuclei as a function of time, you would see a steady trend upwards in mass from 1955 to 1995, let’s say. And now it’s gone back because with the ability to accelerate unstable nuclei, we’re going back and studying light nuclei that we couldn't get to before. So anyway, Yale had this tandem—

Zierler:

What changed in 1995?

Casten:

Well, starting in the very late ’80s, we began to realize that we could make and accelerate beams of unstable nuclei and do experiments far off the valley of stability. There are supposed to be about 7,000 nuclei that can exist fleetingly. Only about 280 of those are stable, and all of our models were built up based on either those nuclei or experiments with them to make nuclei very near stability, okay? That’s like trying to understand somebody’s face by looking at their nose, and so the ability to study nuclei far off stability expanded the gene pool of nuclei. Now we’ve been able to access maybe 3,000 nuclei, and that’s changed our theories radically. The idea has never been to study all 3,000 nuclei. It’s to study specific nuclei that amplify some physics or access some special questions or whatever, but it’s changed things dramatically. So starting roughly early ’90s, there were facilities that could do this. That grew and grew and grew and grew, and now the largest, the main growth area in nuclear physics worldwide, is these radioactive beam facilities. There are billion-dollar facilities in Japan called RIKEN, in Europe called CERN (or at CERN) and GSI, and in the US with FRIB.

Zierler:

Now when you talk about—

Casten:

I’m sorry. Just let me finish the answer. With those facilities, the place where you can go percentage-wise the furthest off stability is light nuclei, and you can study shell structure, various other effects now. So in a sense it’s back to the future. It’s back to where it started, but with access to a much broader range of nuclei.

Zierler:

So is this to say, when you're talking about focusing on particular atoms, that there’s a certain amount of—

Casten:

Nuclei, nuclei.

Zierler:

Oh, nuclei. When you focus on particular nuclei, is the idea that you can extrapolate based on what you're seeing from not all of them, but picking out a few of them?

Casten:

Well, yeah, in a sense. The idea is that up until through the ’70s, let’s say, ’80s, you were trying to extrapolate to the whole face from the nose. Now we’re trying to extrapolate to the whole face from sort of the eyes and cheeks out, so it’s much easier. And we have a whole new understanding of nuclei now.

Zierler:

Right, right. Now to go back to your initial impressions at Yale, you said that the nuclear physics faculty was quite impressive. Were there particular professors that you knew you wanted to work with from day one?

Casten:

If by day one you mean the day I arrived at Yale, the answer is yes. There was a guy, very well-known, famous guy now—well, he’s dead—Allan Bromley.

Zierler:

Yeah.

Casten:

I later became the D. Allan Bromley Professor.

Zierler:

Right.

Casten:

Yeah. So he was there. He was the one who proposed, built, directed for decades the tandem facility there, and he was by far one of the best nuclear physicists in the world.

Zierler:

What was his research? What was Bromley’s research when you arrived? What was he working on?

Casten:

Well, when I arrived they hadn't built the accelerator, so he was working with lower-energy accelerators on light nuclei like silicon, magnesium, carbon. He was Canadian. He had been at Chalk River, which was one of the dominant labs in the world then. In fact, in the late ’50s, the journal one would often go to most prominently was the Canadian Journal of Physics. It’s really amazing. So he came to Yale, and I wanted to work with him.

Zierler:

What were some of the major questions that were being asked in those days in nuclear physics?

Casten:

I guess I would say basically understanding the structure of nuclei, and by that… There have always been two themes in understanding nuclei. One is what the individual protons and neutrons do. Qualitatively they go in orbits around the nucleus 1021 times per second, but they also interact with each other and those interactions lead to collective effects. Just like if you have a flock of birds, each bird is an individual, and yet they have correlated motions to the sky. Or if you’ve ever been to Tanzania and seen the migration of the wildebeests across the Mara River, each wildebeest is an individual wildebeest, but tens of thousands go together. So the second facet is collective motion, coherence among the nucleons, and those are the two themes… Those were the two themes then, and they still are now, in fact. One specific theme which is kind of interesting—there’s a force called the Coriolis force. You know about it?

Zierler:

No.

Casten:

Okay. It’s a force that affects a body on a rotating system. If you want, I’ll explain it trivially.

Zierler:

Absolutely.

Casten:

Imagine you're standing at the equator and you throw a baseball north. It’s not going to go completely north; it’s going to go to the east a little. The reason is because the Earth rotates.

Zierler:

Okay. Right.

Casten:

Rotation speed at the equator is faster than at any higher latitude.

Zierler:

Because it takes… It has more ground to cover.

Casten:

24 hours to go around, and the circumference is largest at the equator.

Zierler:

Right.

Casten:

The ball… Let’s see how I do it for you. So you're looking at the ball. This is north for you. So the ball won't go this way; it will go that way.

Zierler:

Yeah.

Casten:

Okay? It’s an effective force because you're in a rotating system, but it has real effects. For example, rivers in the Northern Hemisphere, south-flowing rivers, tend to be eroded more on one side than on the other. It has all sorts of effects. In fact, I almost wrote a paper once on the effects of the Coriolis force in continental drift. If you look at Africa and South America, they were originally one continent that pulled apart. If you look at a map, you can't just pull them apart like this; you have to rotate them. The Coriolis force is stronger the higher the latitude, and so I thought that that would be what caused that angular deviation. It turns out there were other things it didn't work with, but okay. Anyway, Coriolis force is very— It’s important to nuclei because the protons and neutrons go in orbits, and so if you have a proton going around the nucleus like this, it tends to have a more equatorial orbit due to the Coriolis force.

Zierler:

Okay.

Casten:

If you want one more anecdote…

Zierler:

Please.

Casten:

One of the guys I was in graduate school with—in fact, the first person I worked with on anything was named Joe Allen. Is that a name that resonates with you, Joseph P. Allen?

Zierler:

No.

Casten:

Okay. He did his thesis on sodium isotopes, including the Coriolis force, and then he became an astronaut. He went up on a number of shuttle missions, did space walks, and he always said that the most surprising thing to him when he was repairing some satellite up in space is when he took a screwdriver and put his arm out straight to turn the screw, his arm would go off to the side due to the Coriolis force.

Zierler:

Amazing!

Casten:

Okay, yeah. Amazing. So anyway, there are lots of questions in nuclei, but nucleon orbits, which means shell structure, magic numbers if you know about those, are one thing. That’s the single particle aspect, and the other is the collective aspect of coherent motion like nuclei can rotate. Nuclei that are not spherical can rotate. . Yeah, like this, let’s say, or like this.

Zierler:

Now you said earlier that graduating from Holy Cross, you weren’t sure if you wanted to focus on theory or experimentation. At what point did you make that decision at Yale?

Casten:

Instantly because of this facility, which was an experimental facility.

Zierler:

Right, right. What was the breakdown of coursework and lab responsibilities during your first few years at Yale?

Casten:

By lab you mean like being a TA?

Zierler:

No, like actually working in the laboratory.

Casten:

Oh, okay. The first year was fully coursework. The second year, the first semester was coursework. Well, the first year in the summer I worked at the lab, and then the second year was mostly coursework. Then I would guess late spring of the second year it became almost fully work at the lab.

Zierler:

Now you mention that that first year was brutal because you didn't feel very well prepared relative to your other fellow students.

Casten:

Yeah. I averaged getting to sleep about 3:30 in the morning.

Zierler:

Mm-hmm [yes], mm-hmm [yes].

Casten:

And to this day, as you might remember from an email, I’m a night person.

Zierler:

Right.

Casten:

I seldom get to sleep before 1:00, often 1:30.

Zierler:

Mm-hmm [yes], mm-hmm [yes]. So you caught up mostly by your second year from hard work and study.

Casten:

Yeah. In the first year, my grades were kind of average and with a lot of struggling to get there. By the second year, it was okay.

Zierler:

At what point did you start to settle on a dissertation topic?

Casten:

[Pauses] Basically pretty much right from the beginning.

Zierler:

Oh.

Casten:

In those days, professor/student relations were a little different than today. You got told what you were going to study, and I was told I was going to study something called Coulomb excitation in the osmium isotopes.

Zierler:

Was this directly relevant to Bromley’s research?

Casten:

Yes. There was another professor there named Jack Greenberg, and actually they were my co-advisors. But I had more contact with Bromley.

Zierler:

What were the major questions and challenges surrounding this research question that would become your dissertation?

Casten:

Okay. So the osmium isotopes are heavy. They have Z=76. They’re in a region of nuclei from samarium (Z=62) to mercury that are largely deformed, non-spherical in shape, and they rotate and they vibrate. The osmium isotopes are a transitional set of isotopes where the light osmium isotopes are pretty much normal deformed nuclei. They look like American footballs sort of. As you get to the heavier isotopes, the amount of elongation decreases. They become a little closer to spherical, but they also become axially asymmetric. Now this is not going to show up in the audio, but I’ll do it anyway. Imagine this is a nucleus.

Zierler:

Okay, that’s a rolled up sheet of paper. Got it.

Casten:

And it’s symmetrical if you look end-on. It’s an axially symmetric nucleus. It’s symmetric about this axis going through. But you can also have nuclei like this, and more commonly you can have nuclei—this is going to be very difficult—that oscillate back and forth through different asymmetries. Okay?

Zierler:

Okay.

Casten:

Osmium isotopes are the prime example of that. So the idea was to study transition rates, squares of reduced matrix elements in 186, 188, 190, 192 osmium to see the evolution of this structure. At the time, there was a brand new theory, a microscopic theory, by two people, Kumar and Baranger, that was very exciting because they had achieved some things that nobody had been able to do, and so the specific purpose was to test that theory.

Zierler:

How long did it take you to complete the dissertation?

Casten:

Four years. I started in September of ’63 and my thesis defense was either August 16 or August 18 of ’67. I think August 18th.

Zierler:

What were some of your principle findings?

Casten:

I was, by the way, the first graduate student to get a PhD from the new facility.

Zierler:

Oh, is that right?

Casten:

Yeah, which is ironic because I later became director of the facility.

Zierler:

[Laughs] Rick, what—

Casten:

When I became director, the administrative assistant was the same person who had been Bromley’s administrative assistant.

Zierler:

Oh, wow!

Casten:

And I was still scared to death of her, too.

Zierler:

[Laughs] Rick, what were some of your principle findings in your dissertation?

Casten:

Well, so what I measured technically are called B(E2) values. That doesn't matter. They’re transition matrix elements, so they depend on the relation of the structure of an excited state and a lower state, okay? From that you can get information about the deformation, the elongation, ellipsoidality of the nucleus, and the asymmetry. So the idea was to test those and specifically to compare with the Kumar-Baranger predictions. It was the first test of those, and it turned out the model worked extremely well. So that was, I guess, the main upshot.

Zierler:

Who was on your committee?

Casten:

Oh my god!

Zierler:

[Laughs] These things matter.

Casten:

Bromley, Greenberg, Bockelman, who was, I guess, the chair of the department then, or maybe he had stepped down as chair. Greenberg, Bromley, Bockelman, and there must have been one other. Oh my god. I can't remember. There must have been another.

Zierler:

Okay. When you come back to the transcript, if you want to pull it down off the shelf, you can always add a name later on.

Casten:

I’m not sure the whole committee is actually listed in the thesis.

Zierler:

Okay, okay. Rick, when you graduated, was the draft on your mind? Was that something to think about?

Casten:

Yes and no. Mostly no because I have… Well, this is a longer story, but I have serious asthma. I only have 30% lung capacity, but we’ve got to come back to that because it’s changed in dramatic ways now. But anyway, I could never have been drafted. Let me put it this way. I could not run full speed around a tennis court. I just mean one loop around it.

Zierler:

Right, right. Did you officially get a physical deferment or that wasn’t even necessary?

Casten:

No, no. It just never came up.

Zierler:

It never came up.

Casten:

So I guess technically the asthma wasn’t an issue because I never got called.

Zierler:

Right.

Casten:

So I just never got called, but in those days if you were a student you didn't get called.

Zierler:

When did the opportunity for the Niels Bohr Institute in Copenhagen… Did that come up before you defended? You had that put together, or that was afterwards?

Casten:

No, no. I had the position. I applied to a number of places: Pittsburgh, Seattle, Copenhagen…oh, Orsay in Paris. Maybe Oak Ridge; I’m not sure. Anyway, when I got the possibility to go to Niels Bohr Institute, I grabbed it.

Zierler:

That was the best opportunity for you.

Casten:

That was the best thing you could imagine. In fact, when I told Pittsburgh that I couldn't take their post-doc, the guy I would have worked with there was a guy named Juerg Saladin, who recently died, who also did Coulomb excitation. He wrote me back a letter saying that I made a great decision not to come there. “You go to Niels Bohr.” It was just fantastic.

Zierler:

What about your research at Yale made Niels Bohr such a good fit for how you wanted to continue your work?

Casten:

Well, so as we discussed, my emphasis was on collective effects—rotations, shapes of nuclei—and at Niels Bohr Institute, the two leading people were Aage Bohr and Ben Mottelson. You know those names?

Zierler:

Sure!

Casten:

Okay. So they later won a Nobel Prize in ’75, and their work was on collective properties of nuclei. Aage Bohr was Niels Bohr’s son, and Ben Mottelson was actually American. Is. Well no, he’s Danish now, and still alive. So they were the best in the world. Anybody who could get there pretty much wanted to go there.

Zierler:

Were you looking to continue on with the research that you had done, or was this an opportunity to pursue new projects in Copenhagen?

Casten:

When I went there I didn't know, but I got involved very soon in doing a different kind of study. So Coulomb excitation is a process where you take a target nucleus and you bring in another nucleus. The charge of the protons keeps them apart. They don't actually make contact, and so it goes like this. One does a flyby, and because of the electromagnetic field, it excites the target nucleus, okay? So it’s a sort of long-distance collective effect. What I studied in Copenhagen was what we called transfer reactions. Transfer reaction—here’s your target nucleus. A deuteron—we used deuterons—comes in above the Coulomb barrier. A deuteron only has one charge, so it can get in easily. It’s not repelled very much. So it gets into the nucleus. A neutron gets stripped off that deuteron—a deuteron is a proton and a neutron—and out comes the proton. So by studying the energies of that proton, we can find out what orbit the neutron went in in the nucleus. So that was explicitly studying single particle motion, so sort of the opposite of collective. I studied that in hafnium and tungsten isotopes, and the main part of that study was in fact studying Coriolis effects. We did the first extensive Coriolis calculations as part of that work.

Zierler:

Did you have access to good laboratory instruments in Copenhagen?

Casten:

Yeah, yeah. For the time, yeah. Today they would be laughable, but yeah, at the time.

Zierler:

Right, right. What was the research culture like at the Institute? Were people collaborating? Were they sharing ideas in seminars, even at the lunch table? What was that like?

Casten:

That was one of the most amazing… The Institute was just an absolutely astonishing place.

Zierler:

Yeah.

Casten:

There were all sorts of interactions and discussions. Everybody knew what everybody else was doing. Everybody talked about it. It was a very friendly group. We socialized, and okay. One thing you have to know about Niels Bohr Institute. There were two sites. One was in Copenhagen, the original Niels Bohr Institute. The other was a lab in a town called Risø about 30 miles outside of town. That’s where the tandem was. So if you were doing work at the tandem, you were out there, and otherwise you could be in town. But every Monday morning they had what’s called the Monday morning experimental group meeting, and so all the physicists went to… Whoops. I should say physicists and chemists. Some of them were nuclear chemists. Went to Copenhagen and we had a meeting where usually a couple of experimentalists would tell about what they’re doing, and Bohr and Mottelson and the other faculty would be sitting in the front row and they’d comment on it and often fight about it. It was just fantastic. I remember Bohr and Mottelson once fighting over a Clebsch-Gordon coefficient. Each one of them refused to look it up. They thought they could derive it, but they got different answers. [Laughs] It was just an amazing atmosphere.

Zierler:

Who were some of the major people that would visit the Niels Bohr when you were there?

Casten:

You mean as post-docs like me or senior scientists?

Zierler:

No, senior people, big shots in the field.

Casten:

A lot of them. Strutinsky came from Russia. He’s one of the few that were allowed out of Russia in those days. He’s very well-known for something called Strutinsky normalization. Oh god, I’m trying to remember. There were a lot of people coming through. Anybody who was in Europe who had the opportunity to come by would come and give a seminar. Plus—

Zierler:

Rick, I’m curious—

Casten:

Yeah?

Zierler:

No, please go ahead.

Casten:

The scientists there were absolutely world-class. I mean there was not just Bohr and Mottelson. There was Aage Winther. There was Bent Elbek, Sven Bjørnholm, Gudrun Hagemann, Geirr Sletten, — just loads and loads of really excellent scientists.

Zierler:

I’m curious. On the social scene, you were there in the late 1960s. Did Copenhagen… Was the counterculture… Did that arrive in Copenhagen? Did you experience any of that?

Casten:

By that, you mean like the drug culture and stuff like that?

Zierler:

The whole everything. I mean, the civil rights movement, anti-war protests…

Casten:

No, I was a little early. I was there from ’67 to ’69, and there was some anti… It wasn’t a big thing. When I came back—

Zierler:

Anti-Americanism was not a palpable issue for you?

Casten:

No, no. No, not at all. ’68 was the year of all the riots—no, riots is the wrong word—demonstrations, the student demonstrations in Europe, in France and so on. So yeah, there was part of that, but I wouldn't call it counterculture, not in the sense that we think of the word today. And there was little or no anti-Americanism. Yeah. There were no drugs that I can recall. There was one very nice thing about Copenhagen. First of all, the girls are beautiful, and 1968 was the year of the mini and the microskirt, so it was a joy to walk down the streets.

Zierler:

[Laughs] How did the opportunity at Los Alamos come up?

Casten:

When I was finishing at the Niels Bohr Institute after two years, I applied to a bunch of places. You're going to ask me where. Oh god. Seattle, Los Alamos—

Zierler:

I’ll give you an easier question. So you were looking both at faculty positions and national lab jobs.

Casten:

No. I was looking at post-docs, a second post-doc. In those days, most people who could wanted to take two post-docs.

Zierler:

What’s the thinking there? Why not get started with your full-time career?

Casten:

More training, diversify what you know. Los Alamos had a unique facility also. It had a little baby tandem. I mean nothing like the one at Yale, but they had a triton beam.

Zierler:

What is that? What’s a triton beam?

Casten:

Tritium is an isotope of hydrogen, but it happens to be radioactive with like a 12-year half-life. So almost no facilities in the world use it to accelerate it because it would contaminate the whole facility for decades. Los Alamos had a tandem where they had a triton beam, and you could do experiments with that that were really unique. So that was one of the main reasons. I went there and I worked mostly with a guy named Ole Hansen, who was Danish and who had been at the Niels Bohr Institute. In fact, he was there the first year I was in Copenhagen. The second year he went to Los Alamos and I actually got his position that second year. I mean I filled that slot. So he and I knew each other and I went to Los Alamos mostly to work with him.

Zierler:

Leaving the Niels Bohr Institute, what were some of the big things that you had learned since your time there?

Casten:

Physics-wise.

Zierler:

Physics and just sort of your maturation as a professional.

Casten:

Well, so my PhD thesis was primarily on collective effects. My work at Niels Bohr was mostly on what you’d call single particle, individual nucleon behavior, these orbits the neutron would go into. So it was kind of the blending of those two things, the merging of the collective and single particle aspects, and that’s dominated everything I’ve done since then. I also managed to learn Danish, which is a wonderful language because it has no grammar. They say I am, we am, you am, they am, and they don't pronounce any of the letters, so all the words sound the same. So it’s a fun language. We also discovered a new lifelong love while in Europe, namely, mountains, glaciers and the geology that drives them. This in turn has led to really extensive travels, to all 7 continents, about 90 countries, Mt Everest, the Alaskan and Patagonian wildernesses, etc.

Zierler:

When you were at Los Alamos, were you part of the classified world at all?

Casten:

No. I had a clearance because you had to have one, but as far as I know, I never learned a classified fact.

Zierler:

So what was your major work while you were at Los Alamos?

Casten:

Well, using this triton beam—and it wasn’t the only thing, but it was probably 90% of it. Using the triton beam to do reactions called (t,p). A triton is a proton and two neutrons, and so if you send it and bombard a nucleus, those two neutrons can get stripped off, okay, and go into the nucleus, and then the proton goes out. You measure the energies and angles of the proton with a spectrometer and you can tell about those two neutrons that went into the nucleus. The two neutrons go in as a pair, so instead of studying single particle effects like with this (t,p) reaction, now we’re studying correlations of two neutrons in the nucleus. It also has the advantage that it’s one of the few reactions (or was then) where you could go more neutron-rich than stable nuclei. If you take the heaviest stable isotope and add two neutrons to it, you're studying an unstable nucleus. So it was a way to do a small excursion off into the unknown. The (t,p) reaction is very nice because it has very simple properties, but you can learn a lot. So we did that on a whole bunch of nuclei ranging from probably beryllium up to plutonium.

Zierler:

Were you publishing and presenting at conferences a lot during your time at Los Alamos?

Casten:

Oh yeah, yeah, yeah. Also at Niels Bohr.

Zierler:

I’m curious, Rick. Over these four years of your post-doc life, how had the world of theory changed as a result of all of the advances that were happening in nuclear physics on the experimentation side?

Casten:

Well, the study of collective effects—you can call that sort of the Bohr-Mottelson approach, although that’s not completely fair to them. Their Nobel Prize actually involved individual particle effects also, but let’s say that. That was developing with the Kumar-Baranger model and other calculations, so it was understanding collective effects. There’s another aspect that I’ll come back to in a second. And the study of shell structure individual particle motion. It’s the same themes all the time. Understanding the relation between the two. There had been major developments because of tandem accelerators. There was another thing, which is this, that the more… The heavier the nuclei you can bombard—and remember, with tandems we can now overcome the Coulomb repulsion between the protons in two nuclei and combine them, fuse them. This nucleus that comes in doesn't just fuse; it brings in momentum and it brings in angular momentum, okay? So imagine… I realize for an oral history this isn't going to work, but that’s okay. So imagine this is a target nucleus and here comes a projectile. When this projectile comes in, it makes this nucleus rotate, okay? Clear?

Zierler:

Yeah.

Casten:

So we can bring in lots of angular momentum. When I was a graduate student… So what’s your background? Are you a scientist or what are you?

Zierler:

No, I’m a historian.

Casten:

Oh my god.

Zierler:

But you're doing great. This is… You know, you're conveying this to a broad audience, but I’m tracking with you. Keep going.

Casten:

So there’s a thing called spin, or angular momentum, and all quantum systems have angular momentum. And all quantum systems have states, different configurations that can exist. One of the characteristics of those states is their spin, their angular momentum. The technical term is angular momentum. In nuclear physics we call it (incorrectly) spin. Okay? When I was… If you take a nucleus with an even number of protons and an even number of neutrons, the lowest state, the ground state, always has angular momentum zero. Then you can have excited states with angular momentum 2, 4, and so on. When I was a graduate student, the last paragraphs of my thesis said something like, “Maybe in the future we’ll be able to study high spin states like the 6+…” By the early ’70s, people were studying 20+, 30+, 40+ due to the huge amount of angular momentum that could be brought in. So that was a growing field starting in the early ’70s and actually dominated nuclear structure physics until the early ’90s. I never got into it really, but it dominated the field. And then there was a triple revolution at the time. There have been two triple revolutions in the field. One was in the late ’60s and the other was in late ’90s, let’s say. Both led to renaissances in the field, and they were both triple revolutions. In the ’60s, it was beginning to be the first use of computers; the development of a new generation of detectors for gamma rays, called germanium detectors. They were made of germanium; they didn't detect germanium. They detected gamma rays. In fact, the very first thing I did at Yale, very first research I ever did was to build germanium detectors with Joe Allen. We stopped after a while because Chalk River was doing it and they blew us out of the water, but anyway. So computers, germanium detectors, and tandem accelerators. In other words, new accelerators. In the last 20 years, same thing has occurred: development of accelerators that can accelerate exotic nuclei, unstable nuclei; the development of detectors to analyze that data; and the computers to deal with it. Okay? I guess we’re going to come back to that, but let me, in parentheses, make a comment.

Zierler:

Sure.

Casten:

We now have the ability to study these exotic nuclei far, far from the valley of stability.

Zierler:

What is the valley of stability? What does that mean?

Casten:

So okay. Only certain nuclei are stable in nature, okay? Only nuclei with certain numbers of protons and neutrons. In light nuclei, those tend to be nuclei with approximately equal numbers of protons and neutrons. The reason is simple. If you have too many protons in a nucleus… The nucleus is held together by the strong force, but the protons are charged. So if you have too many protons in a nucleus, the nucleus will just fall apart. The protons will repel each other and it will break up, okay? On the other side, the nucleons in the nucleus occupy quantum levels, and because of something called the Pauli principle, you can only put a certain number of nucleons in a given level. So imagine that this coffee cup is a hole where you can put these particles. You can only put certain numbers of neutrons or protons at the bottom, and then the next level is a quantum state up higher. You fill that; you fill that; you fill that; you fill that. Once you fill up to here, the nucleons don't stay in. They fall out. It’s called a drip line for obvious reasons.

Zierler:

Sure.

Casten:

Imagine filling it with coffee, except the coffee fills continuously and the nucleons fill discretely, but that’s a detail. Anyway, so you also can't put an infinite number of neutrons in a nucleus. They will spill out, okay? So why did I say all this? What was the question?

Zierler:

[Chuckles] Well, we’re talking about the two big revolutions, the one in the late ’60s and the one in the ’90s.

Casten:

Oh yeah, yeah. Okay, okay, okay. Oh, you asked what the valley of stability is.

Zierler:

Right.

Casten:

The valley of stability is the set of nuclei that are stable, and in light nuclei, those have approximately equal numbers of protons and neutrons. In heavier nuclei, there are more neutrons because the charge of the protons would blow up the nucleus, and the neutrons help keep them apart, okay, so you have more neutrons. Anyway, beyond that, beyond those 280 or so nuclei, there’s a whole world of thousands and thousands that can exist, and if you can pick and choose specific ones to study, we’ve revolutionized our theories, okay? So the triple revolution in the ’90s was the ability to make accelerators that could accelerate these short-lived nuclei—make and accelerate them. And one detail there is if you do an experiment with a tandem, you have roughly a billion projectile particles per second, otherwise known as a nanoamp, okay? That’s 109 particles per second. With these exotic beam facilities like FRIB, you’ll often be lucky to have 200, so you have to develop detectors that are millions of times more sensitive, literally millions of times. So the second part of the revolution in the ’90s was developing these instruments, these spectrometers and gamma ray detectors that were many orders of magnitude more effective. Thirdly, when you smash these nuclei together, you get a tremendous amount of data and you need the computers to be able to analyze that data as it comes in, and so again, development of computers. Development of computers—

Zierler:

As it comes in, Rick, in real time or you can…

Casten:

Yeah, yeah. In real time.

Zierler:

In real time.

Casten:

The other aspect of computers is that there have been major… I don't want to say quantum leaps because a quantum leap in popular language is a big thing and in reality it’s a small thing. But anyway, giant leaps forward in theory. The nuclear theory now is just totally different than it was in the ’60s because of the use of massive computers to solve problems that couldn't even be begun to be looked at. Anyway, so those two triple revolutions half a century apart, or 40 years apart, have controlled nuclear structure physics. I’ve got to take a moment to clear my throat. I’ve got something caught.

Zierler:

Please. Take your time.

Casten:

[Clears throat] Oh, that was quick. Okay, done. All right, so where were we?

Zierler:

So in what ways was Los Alamos a great place for you to continue with your research?

Casten:

Well, the facility for triton beams. The people, Ole Hansen in particular who was absolutely brilliant. The area—I love Santa Fe. It’s a wonderful town. I still go out there six weeks a year to do research at Los Alamos. It’s a mixture of—I don't know if these are the politically correct terms—Anglo, Indian, and what’s called Chicano, which is what you would call Hispanic, I guess, cultures in the city. It’s just an amazing mixture of these. Historically, archeologically, geographically, it’s a fascinating area, so it’s a wonderful place. And we met lifetime friends there, Bob and Marian Haight, who we often see, have traveled with. He was a scientist at LANL, although we never explicitly worked together.

Zierler:

Now the opportunity at Brookhaven, that was a full-time… That was a permanent job.

Casten:

That was my first non-post-doc job. It was at the assistant physicist level, like assistant professor.

Zierler:

Right, right. Were you recruited there? Did you apply for an open position?

Casten:

I applied. No, no, no, no, no. No. As I remember, I didn't apply like just sending in an application. I don't remember exactly how it came up. I know it happened very quickly. There was a possibility of a position. I wrote a letter. A couple of days later I got a phone call. A couple of days after that I was in Brookhaven being interviewed, and I got the job. So it couldn't have been a normal application process. There must have been some opening that somebody knew about.

Zierler:

What was the position? What would you be doing at Brookhaven?

Casten:

The position was actually very different, and in fact, most people I knew thought it was going to be a dead end. It was to work at the nuclear reactor there to do neutron capture experiments. These are experiments where you get a beam of neutrons from the reactor. Neutrons impinge on a nucleus. They have no charge, so they can get in easily. They make a new nucleus and you study that nucleus by using the neutrons to get into it.

Zierler:

What was some of the major research that was going on at Brookhaven in those days that you would be joining?

Casten:

The answer is different after your last five words. The major research going on at Brookhaven in my field then was at the tandem. They had a double tandem—that’s two tandems back-to-back—which were each the same accelerator exactly as had been built at Yale.

Zierler:

What does a double tandem do that a single tandem doesn't?

Casten:

One and a half times the energy. That tandem is called an MP tandem, and Yale had MP-1, and I think Brookhaven had MP-6 and 7. Rochester had MP-2 and so on. MP—I don't even know what MP stands for, but it got to be a word, emperor, and in fact the tandem at Yale was called the Emperor tandem. And sometimes Bromley was called the emperor. Okay. So that was the main activity. The reactor was a fringe activity. But it gave the opportunity to study lots… Let me say it differently. With everything I had done up to then, Coulomb excitation or dropping neutrons into the nucleus, generally you're taking a target nucleus and exciting the lowest levels of the daughter nucleus. Is that clear?

Zierler:

Mm-hmm [yes].

Casten:

Sorry. Taking a target nucleus and either exciting levels in that nucleus by exciting them with a Coulomb force, or tossing a neutron in and exciting the low-lying states of the nucleus. Or at Los Alamos, tossing two neutrons in and studying low-lying excited states. When a neutron gets captured by the nucleus, it forms the new nucleus at a very high energy, and so now you can study all the intermediate states going down. You get a cascade of gamma rays going down, down, down in energy toward the ground state. It gives you access to a much wider range of states, some collective, some single particle, some mixtures. So it’s a new window, a different window into the nucleus.

Zierler:

In what ways was the physics and the research culture at Brookhaven different than at Los Alamos?

Casten:

[Pauses] Not so different. The people were different because the whole culture out west in Santa Fe was different, but basically it was similar. Groups were about the same size. The people in my field at each place were 10 or 15 people.

Zierler:

And who were some of your key collaborators during your time at Brookhaven?

Casten:

Well, I guess that’s one way it differed. I worked much more on my own.

Zierler:

Oh, you did.

Casten:

Yeah. I mean basically I worked on my own. I did the experiments myself. Well, I worked with a guy named Walter Kane, and he was the group leader until I became the group leader. But pretty much I worked independently, and sometimes I would hire post-docs and I would work with them. I also brought in visitors, often for a year, sometimes much more, or new staff members. Two in particular, both brilliant, were Dave Warner and Victor Zamfir.

Zierler:

Did you have a budget that allowed you to build up your lab the way you saw best?

Casten:

[Clears his throat] Sorry, I haven't talked this much in a while. With my wife I don't get… Actually, we’d better delete that. [Laughter] Sometimes I get to finish a sentence. Budgets were not a big problem. I don't remember really having to worry too much about that. I mean I know we had a budget and we were limited by that, but it allowed us to do what we wanted to do.

Zierler:

What do you feel were some of your main accomplishments during your tenure at Brookhaven?

Casten:

I would split it into… Just wait a minute. Let me think about this. I would divide it up into three stages. The first few years from ’71 to about ’77, ’76 were sort of putting the (n, ?) reaction on the map, showing what it could do, working on a technique called average neutron capture which was a way of guaranteeing that you would see all excited states with certain ranges of angular momentum in the nucleus up to some energy, which kind of really turned (n, ?) around and made it a serious tool. So that was phase one. The second phase was an outgrowth of that, studying certain nuclei, in particular platinum-196, which I did with a graduate student from Stony Brook who worked with me at Brookhaven, Jolie Cizewski. She’s a professor at Rutgers now. We studied this nucleus, 196Pt. I spent a sabbatical in Grenoble at that same time, and they had absolutely unbelievable instruments at their reactor. If you want, I can take a side bar and tell you about that.

Zierler:

Please!

Casten:

Okay. So when I was a beginning graduate student… No, let me go back. Energies of gamma rays in nuclei are measured in kilovolts. It’s a unit called keV. It doesn't matter if you know what they are. A kilovolt is 1000 electron volts, okay? When I was a graduate student, the sensitivity, the resolution, the accuracy of energy of a gamma ray transition measured with a so-called sodium iodide detector was typically 5-10 kilovolts. When I was a graduate student I worked on these detectors called germanium detectors, remember I mentioned, with Joe Allen?

Zierler:

Mm-hmm [yes].

Casten:

Those were new in the late ’60s, and with those you could measure a gamma ray to 0.1-0.2 kilovolts, okay, so 50 times more accurate. That was a big advance, and that’s still the standard today. The gamma ray detectors today are much bigger, orders of magnitude more sensitive, but about 2 kilovolts is still the standard for energy resolution (about 0.2 kilovolts for accuracy). They had an instrument in Grenoble which could measure gamma rays to 1 electron volt, 200 times better, and that was revolutionary. And another, called BILL, that could measure conversion electron energies to comparable accuracy. So I spent a year in Grenoble using this instrument, two instruments actually, on platinum-196 and other nuclei, but mostly platinum-196. I worked with a super scientist Hans Boerner, who built GAMS and was a genius at using precision to advance science, another Klaus Schreckenbach who built BILL, Dave Warner, whom I have already mentioned, and others. My graduate student Jolie was back at Brookhaven doing (n, ?) at the reactor on platinum-196. When we got back, we combined the results, saw some really weird things in the structure, in the level scheme. At exactly that time, a guy named Franco Iachello, who I’m sure you know about, was at Yale. Well, had he gone to Yale yet? Anyway, he was around and his approach to nuclear physics, to all kinds of physics was through group theory. It’s a branch of mathematics. He had developed a model called the interacting boson model, or interacting boson approximation model with Akito Arima, a Japanese physicist, which was attracting a lot of attention. It made the prediction of a new symmetry, a new kind of structure for nuclei. The technical term is called O(6). Anyway, the nucleus that he thought might look like this O(6) symmetry was platinum-196. So he visited us at Brookhaven and we had this really weird conversation. Jolie and I talked to him and said, “We have this level scheme and it has some very strange patterns to it,” and he said, “I have this symmetry and it has some very strange patterns to it.” We compared them and they were almost identical, so it just blew our minds. So from ’77 on actually until today, a lot of my research has been involved with studying symmetries in nuclei. Symmetries are structures that can be described very simply, often parameter-free. They tend to have a geometrical meaning. A given symmetry corresponds to a certain geometrical shape in the nucleus. Okay, and so the second phase from late ’70s on until I left in ’95 (or ’98 technically) was basically studying symmetries. Okay? In the third part in parallel with that… All right. Remind me to come back to the question of theory.

Zierler:

Okay.

Casten:

The third part of that was in ’81 I became group leader of the group. The group had another facility called TRISTAN, as in Tristan and Isolde. There was a similar facility at CERN called ISOLDE.

Zierler:

Ah. Okay.

Casten:

This was a facility to study exotic nuclei in a much more primitive way than we can now, but it was a start. When I became group leader, I also became group leader of that part of the group’s effort, which I hadn't paid too much attention to up until then. So the third phase was working and developing physics with TRISTAN with a lot of collaborators from around the world. Okay. I want to make a comment on theory.

Zierler:

Please.

Casten:

Some misguided people think I’m a theorist, which I’m not. I’m an experimentalist. But I’m what you’d call a theoretically inclined experimentalist. I’ve published a bunch of papers that are theoretical, and I’ve done a bunch of—I hate to use the word because it has a negative context, but I’ll say it—phenomenological papers. These are papers that look at various correlations of observables, okay, to try to understand what drives the evolution of structure in nuclei. So in this period starting in ’78 or so up until now, a significant part of my research has been theory-related, okay, trying to understand why nuclei do what they do, and so at Brookhaven I also did a lot of that. Okay.

Zierler:

I’m curious, Rick, in terms of when you felt compelled to work on theory, is that because you were dissatisfied with the work that was already out there? Do you feel like you needed to step in because it wasn’t being done absent what you were able to accomplish?

Casten:

No. First of all, I didn't feel compelled to work on theory. I felt attracted to it. No—

Zierler:

Mm-hmm [yes]. But I mean in terms of like your reliance on theory being advanced for your experimentation. Did you feel like there was that need and it wasn’t out there so you had to fill that in?

Casten:

No, that’s not an accurate way to say it. Let me think. No, I think it was more an opportunity. I had always—okay. I had always been somewhat theoretically inclined. Back in Copenhagen when we studied the Coriolis effects in nuclei, I wrote the code and did the calculations of that for our little group, so even then I was involved theoretically. Actually, it goes back even further. It goes back to when I first went to Yale. The tandem was being built, and there was a year from ’65 to ’66 when there was really nothing to do for the graduate students because there was no facility. We weren't quite ready to build instruments, and so many of us spent the year just learning nuclear physics, which means nuclear theory. So from the very get-go I was interested in nuclear theory, okay, and I don't mean nuclear theory in the modern sense of these very fancy computer calculations using density functional theory, ab initio and all that, blah, blah, blah. This is simpler theory that you can do with a calculator or with very simple computer codes. One of the reasons why the interacting boson model became so popular—in fact, the most successful collective model for low energy states in nuclei—was because a graduate student, Olaf Scholten, a graduate student of Franco Iachello’s, wrote a computer code that was extremely user-friendly, and people, even miserable experimentalists, could work with it. So I did a lot of IBA calculations.

Zierler:

What’s the value of IBA calculations?

Casten:

Well, this interacting boson model was by far the best model for collective effects in nuclei where it had many, many, many, many fewer parameters than other models. It could be calculated easily and revealed a lot of information about nuclear structure that you couldn't get otherwise very easily. So I became somewhat of an expert on it. In fact, I have co-authored two Rev Mod Physics papers on the model over the years. At Brookhaven, I worked with Dave Warner, who died very young unfortunately, and he was brilliant. He and I first knew each other in Grenoble and then I invited him to Brookhaven. We worked together on some of the theory of the interacting boson model. We invented something called the consistent-Q formalism, which was a simpler way of doing IBA calculations. It had fewer parameters and worked better. It has since become the standard way of doing these calculations. So we just got involved in it. By the way, if you want another anecdote, the first time I went to China was in ’83 or so, and I remember them showing me around and showing me this temple and saying, “We call this the Blue Temple because the tiles on the roof are blue. We call this temple the Heavenly Temple because it’s tall.” I thought, “God, this is stupid,” and then I began to realize if you name something, it takes on a life of its own. If you think about nuclei, most of the time we think about nuclei with even numbers of protons—no. Let me say it differently. We think of nuclei according to the number of protons they have, like aluminum with 11, magnesium with 12, osmium with 76, and so on, because those have names. We don't think of all the nuclei with 24 neutrons…

Zierler:

Right.

Casten:

…because 24 neutrons could be argon. It could be calcium. It could be chromium, okay? So when you name something, it takes on a life of its own. So we published this paper on a revised formulation of the IBA model. Nobody paid any attention to it. The next paper we wrote on it, we gave it a name, the Consistent-Q Formalism, or CQF, and once we named it, it just took off. So it’s really strange. I mean it was the same model, but it had a name people could latch onto. Anyway, that was off the subject. So I got involved in a lot of theoretical things also relating to the importance of the proton-neutron interaction in nuclei.

Zierler:

Do you think your work in theory helped your experiments? Was it a…

Casten:

Oh, absolutely. Absolutely.

Zierler:

It was. In what way?

Casten:

Well, it made me realize what the key things to measure are and also how to interpret the measurements, so it was very much a linkage. The other thing I got involved in theoretically is, as I started to say, the proton-neutron interaction. If you look at especially heavier nuclei and ask what controls the changes in structure as you add neutrons or protons, it’s the interaction of the protons and the neutrons, the outermost. It’s what we call valence protons and neutrons with each other, okay?

Zierler:

Mm-hmm [yes].

Casten:

There was a model developed by Stuart Pittel and Pedro Federman in 1977, 1978 which exploited this to explain some things that couldn’t have been understood before about regions of nuclei where the shape changes very rapidly as you add two neutrons. I developed something called the NpNn scheme. It means number of valence (outer) protons times the number of outer neutrons. The NpNn scheme was able to predict the properties of nuclei not by doing a massive supercomputer calculation, but by multiplying two numbers together, each less than 44—number of outermost neutrons times the number of outermost protons because that simulated the total outermost proton-neutron interactions, okay? So things like that. That was another facet. The valence proton-neutron or p-n interaction is really the key to the evolution of nuclear structure along the nuclear chart. In particular, it accounts for the onset of deformation (non-spherical shapes), especially in regions where this happens very quickly, with, say, a change of only 2 neutrons. I applied these ideas to extend the Federman-Pittel picture to heavier nuclei. With Kris Heyde and Piet Van Isacker from Gent, we developed a model for this that accounted for the rapid onset of deformation in some regions, slow development in others and no deformation in still others, in a simple consistent framework. In more recent times, these ideas have been further formalized in terms of fancy-dancy tensor forces but the basic idea is about the same. This reminds me that I wanted to come back to a question you asked a while ago about why I got involved in theoretical things. Besides what I said above, another reason was simply that I felt I had a different perspective than most theoretical work. Perhaps you could call it a different intuition. The NpNn scheme is a good example of that. It was totally trivial and anyone could have come up with it but I happen to think in ways like that. So it led to some theoretical work. By the way, not all theorists were happy about that kind of approach. One theorist wrote a scathing review of my textbook, whose title itself, Nuclear Structure from a Simple Perspective, reflects my way of thinking and makes the textbook different from others, for better or worse – simpler, more intuitive but hopefully not less rigorous. Simplicity is not the same as hand-waving. Students seem to like it. Another anecdote: In the early days of the IBA model, Aage Bohr, Ben Mottelson, Arthur Kerman, Franco Iachello, Dave Warner, Witek Nazarewicz, Ikuko Hammamoto and myself met at MIT to hash out some disagreements on the model. At one point I was talking about something, and Kerman, a well-known theorist, popped up with what has since become a (jokingly) oft-repeated statement. He said: “Experimentalists should not dabble in thought”. I hope that some of my theoretical work actually contributes. I hope that it may reflect what T. D. Lee once said at a Brookhaven colloquium. He was asked if what he was saying wasn’t awfully simple. He immediately said (and this became a motto for our BNL group, and me personally ever since): “That a thing is simple does not mean that it cannot be deep”.

Zierler:

Now in 1995 it looks like you become dual-headed. You have an ongoing affiliation with Brookhaven, but you start at Yale the same time.

Casten:

Yes.

Zierler:

How did that happen?

Casten:

Well, I got an offer to be the director of the lab at Yale in ’95.

Zierler:

And that’s the WNSL lab?

Casten:

Right.

Zierler:

What does WNSL stand for?

Casten:

Wright (as in Wright brothers) Nuclear Structure Lab.

Zierler:

I see.

Casten:

Wright was the first—I hope I get this right—the first physics PhD at Yale around 1860, so it’s named after him. So WNSL, Wright Nuclear Structure Lab. So I got an offer to come there and be a professor and be director of the lab, and this was very attractive to me partly because that’s where I’d been a graduate student and partly because I felt that I had done what I could at the reactor at BNL. Some of the same people were still there, including this administrator that I was terrified of. So I took that position. Now why didn't I leave Brookhaven until ’98? Two reasons, one of which I’m a little reluctant to say, but I guess I will. First of all, I didn't know how Yale would work out, so I got a two-year leave of absence from Brookhaven so if I didn't like it I could come back. The other thing was that if I had an affiliation with Brookhaven into ’98—that is, until my 50-whatever birthday—and if I came back for a month after this leave of absence, I would then qualify for the Brookhaven medical care system, which was far better than Yale’s.

Zierler:

Government beats the Ivy Leagues, huh?

Casten:

I guess so. [Chuckles] So all my life at Yale I’ve had Brookhaven health system. Still do.

Zierler:

Rick, were you recruited specifically to lead the WNSL or that was…

Casten:

No, it was exactly that.

Zierler:

Mm-hmm [yes]. So the physics faculty appointment was sort of incidental to the lab directorship.

Casten:

No, no, no. They were part and parcel. Actually, what happened was—and I don't know the inner workings of this, but I went to Yale to do an experiment, funny enough on osmium, in May of ’95. While I was there, they asked me to meet with a committee that was looking for a faculty member, okay, to be the new director of the lab. They wanted my advice, so I talked to them. I think it was an interview, although I didn't know it at the time. I think they had thought that they might want to ask me to be the person, but they didn't tell me that. They asked me to come and give them advice about the position. So while I was there doing an experiment, I talked to this committee and gave them my thoughts about what they should do, and then when I got back to Brookhaven a week or so later, they made me an offer.

Zierler:

How far developed was WNSL by the time you arrived?

Casten:

Can I go back 30 years?

Zierler:

Yeah, absolutely!

Casten:

In the ’60s, Yale was far and away the best facility in the world for what it did, and that was due to Bromley. He had an incredible vision. He was a very controversial character. He was a brilliant scientist. He rubbed a lot of people the wrong way. Do you know his subsequent history?

Zierler:

I don't.

Casten:

Oh. He was the science advisor to the first Bush.

Zierler:

Oh, oh. Right, right. Yes, yes.

Casten:

In fact, he was one of the few science advisors who had a cabinet-level position. You know the story about how he became an American citizen?

Zierler:

I don't know that story.

Casten:

It is said that he went out to New Mexico to view a nuclear test, and just before the test they realized that he was Canadian and that was absolutely forbidden. So on the spot they made him a US citizen. In any case, he built up this lab, which was just unbelievable. The people there were great and students were great. Faculty was great. The facility was great, and it remained that way until he… He left for Washington in ’88, and starting then it began to decline seriously, and so by the mid-’90s it was not doing much of anything. The equipment wasn’t up to date. The number of hours they ran per year was small. [Pauses] Yeah, okay. So when I came, one of the first things I did… Oh, and they also had no students and no faculty. They had one faculty member at the tandem. Ah! Things are coming back now. They had one faculty member at the tandem and one graduate student left doing tandem work. There was another guy who was technically at the tandem who was doing other kinds of research. DOE was thinking of closing the facility, so that was probably the reason, which I forgot to say, why they wanted to try to bring in some new people. Hold on. I’m getting some message on my laptop.

Zierler:

Sure.

Casten:

Okay. So I came in. I made what you’d call a deal to hire two new faculty members, junior faculty, and get some what they call nowadays startup money, which was money to buy instrumentation and pay post-docs and stuff like that.

Zierler:

Rick, I’m curious if you felt like you were coming home after all those years after graduate school.

Casten:

Yeah. I mean I had only been to Yale a couple of times in that whole interim, but yeah, it felt very much like home.

Zierler:

Had WNSL made any significant contributions to the field in the 30 years since you had been gone?

Casten:

Oh, yeah. There was a controversial set of experiments on something called nuclear molecules. If you collide two nuclei like two magnesiums, instead of directly fusing they could kind of attach to each other, and because they bring in angular momentum, rotate like a molecule. Okay? Clear?

Zierler:

Yeah.

Casten:

Okay. Bromley pushed this for many years. It was always controversial, but it was an important area. Bromley, by the way, was known as the dean, maybe its the word, of heavy ion nuclear science. In fact, he edited a seven-volume or six-volume book called Treatise on Heavy Ion Science. The whole point of the tandem was to be able to accelerate heavier and heavier nuclei, and since you have to remove an electron to make them charged to accelerate them, they were ions, so heavy ion. They made large contributions in that area, and then over the years they made other contributions in terms of things called giant resonances, isospin, various things, nuclear astrophysics.

Zierler:

What did you feel like your main goals were in assuming this position and looking to take the lab in new directions?

Casten:

Well, to rebuild the facility and make it something like what it was, a leading center for nuclear physics research.

Zierler:

Now by rebuild, does that have both administrative and instrumentation connotations? Were you looking to rebuild personnel and equipment?

Casten:

Both. Not the accelerator itself, which was… Well, we did a little work on the accelerator, but mostly that was there. It wasn’t run very efficiently, but it was there. But no, mostly detectors, instruments, and people—faculty members, post-docs—and we got some really excellent faculty members.

Zierler:

Who were some of your most important—

Casten:

And visitors. We also had scads of visitors come in for anywhere from a month to six months, sabbaticals and things.

Zierler:

Who were some of your most significant recruits?

Casten:

Not in order, but Victor Zamfir. You know the name?

Zierler:

I do, yeah.

Casten:

Wow!

Zierler:

I’ve just heard it. I talk to physicists every day. You know, names come up.

Casten:

God, get a life! [Laughter] So he is somebody I met when I had a sabbatical in Cologne in the mid-’80s. He’s from Romania and he’s very, very good. We have done about 160 papers together, maybe more. When I was at Brookhaven, he came as a kind of post-doc and then he stayed on and became a physicist there. When I came to Yale, he came to Yale and he’s just amazing. He currently is director of a facility called ELI-NP, which is a 10-petawatt laser facility in Bucharest. It’s just finishing construction now, and it’s also an amazing facility. Anyway, he’s one. He’s probably the primary one. He and I did so much research together. So that was one. Another was Reiner Kruecken from Munich who is now the associate director of TRIUMF in Vancouver. You know TRIUMF?

Zierler:

I do not.

Casten:

TRIUMF is the main Canadian nuclear physics facility.

Zierler:

Oh, okay.

Casten:

TRIUMF ends in an F, not a PH and stands for Tri-University Meson Facility. Anyway, he’s associate director of that. Another was Con Beausang who unfortunately died very young. He was an expert on high spin, high angular momentum states. Andreas Heinz, who is now a professor in Göteborg in Sweden. Andreas Zilges came for just a year, sort of a special visitor the first year I was there, and he’s now a professor at University of Cologne. Does very good work on sort of what are called dipole excitations. Norbert Pietralla, who’s a professor and director of an institute in Darmstadt, came for two years. No, he didn't. He came for… He came for a shorter time. I don't remember exactly how long. One of the main ones was Volker Werner, who did his thesis in Cologne when I visited there. He came to Yale for many years and is now also in Darmstadt. Paddy Reagan from Surrey in the UK visited WNSL every summer for many years, sent us many students, and we did a huge amount of work together. The problem is I’m going to forget people and I don't want to because this history has some legs to it. In the edited version, if I can remember who I’m forgetting right now I’ll add them in.

Zierler:

Certainly. This is a very international cast of characters.

Casten:

Oh, yeah. Well, physics, nuclear physics is international. I’ve had connections with Cologne since ’82. I had a Senior Humboldt award thing. It’s a prize in nuclear physics, anyway, which entailed a year working in Germany, so I worked in Cologne with a guy named Peter Brentano, who is also a very well-known guy. Very interesting guy. He just died. Anyway, so for years and years and years I’ve had connections with Cologne. Brentano and I and his students did a lot of stuff with the IBA model and the proton-neutron interaction. In any case, we had so many people from Cologne that some people called us Cologne West. And then Michigan State also has connections with Cologne, and their site is sometimes jokingly called Cologne Far West. So anyway, yeah, a lot of people from Cologne.

Zierler:

Rick, what did you see as you were—

Casten:

Sometime during this I really should talk a little more about the Cologne research because that was a very important part of my career.

Zierler:

So when does that happen? What years is that?

Casten:

Well, I went there for short visits in the early ’80s. (Short visits are a couple of weeks.) Then I spent this year and sabbatical there in ’83 and 4. Oh, that was the Humboldt Prize year.

Zierler:

Oh, I see. Okay. So this is before you get to Yale.

Casten:

Oh yeah, long before.

Zierler:

So let’s talk about that now then. How did that connection develop at Cologne?

Casten:

Well, it developed as I knew Brentano, and he actually was the guy who nominated me for the Humboldt Prize. So I went there and then after that year, every year for about… more than a decade I came back for two months in the summer. Once I went to Yale, it became more and more difficult and I stopped doing it, but I still have lots of contacts. A lot of the stuff I’ve done ever since had its genesis there. In fact, this business about the NpNn scheme, proton-neutron, that really started there. I had that idea during a concert in Cologne. Most of my good ideas have not come from in the lab. That one came at a concert. Another one came in the shower. In fact, yeah, I had an idea once in a shower in a friend’s house in Tennessee. His name is Lee Riedinger, and later when I wrote the paper, the acknowledgements thanked him for providing facilities where some of the work was done—namely, his shower. Anyway, so Cologne played a really seminal role, and after that there were a lot of people from Cologne… Oh! You're at the APS or AIP. So you know I’m an editor for Phys Rev C?

Zierler:

I do.

Casten:

Okay. The managing editor for Phys Rev C is Chris Wesselborg. Know him?

Zierler:

I know of him.

Casten:

All right. He was a graduate student at Cologne when I was there that year. I later hired him at Brookhaven as a post-doc, and then it was only a couple of miles to switch to Ridge where he is now at Phys Rev. So that’s just one example. Reiny Schumann was also one of my post-docs. You know that name?

Zierler:

I don't, no.

Casten:

He’s high up at APS physics… at the journals. Anyway, so I’ve long had a string of people from Cologne that I’ve done research with.

Zierler:

In what ways was Cologne doing different research than what you were doing at Brookhaven? Obviously there were dovetails, but what were the differences?

Casten:

Well, the experimental techniques were totally different. At Brookhaven I was doing (n, ?) at a reactor, which means taking slow neutrons, letting them fall into nuclei, and looking at the states that were excited. In Cologne they had a tandem, not as big a tandem as Yale… Oh, remind me to make a comment about that. Just say small tandem to remind me. They had a lot of nice instruments. Brentano was a brilliant leader there, and they were doing a lot of… A lot of the physics themes were similar: collective effects, interacting boson model, and so on. The experimental techniques were very different. A comment about small tandems. A lot of what I said seemed to imply that advances in research resulted from these amazing new facilities.

Zierler:

Right.

Casten:

However, more important than that are the people. Brentano was the director in Cologne from roughly 1976 until Parkinson’s started to show up, mid-’90s or so. The tandem there was obsolete before it was built.

Zierler:

What happened?

Casten:

It was built after the Yale tandem.

Zierler:

Oh.

Casten:

And it was much lower energy. It was really a primitive instrument. And yet for decades, they were, in my opinion, the leading nuclear structure facility in Europe, and they did amazing research because this guy was clever and he attracted clever people. In fact, his students and progeny dominate a lot of European nuclear physics. At MSU, this FRIB facility, the project director is Thomas Glasmacher—known as Thomas [changing pronunciation], not Thomas, but he’s Thomas—who started off in Cologne. Alex Gade is one of their brilliant young professors. She was a student of Brentano’s in Cologne. Michael Thoennessen—you know that name, I’m sure.

Zierler:

I do, I do.

Casten:

Yeah. He started off in Cologne.

Zierler:

Oh, wow.

Casten:

And I’m forgetting others. There are a whole bunch who originated in Cologne. Norbert Pietralla and Volker Werner, who I mentioned before, were both from Cologne. Hendrik Schatz, who you may know that name; I don't know.

Zierler:

No.

Casten:

He is a nuclear astrophysicist. Had no connection with Cologne, but he came from Germany. There are these linkages.

Zierler:

Right.

Casten:

Anyway, so I’ve long had an association with Cologne and some of my best ideas were formed either there or related to work and discussions there.

Zierler:

Mm-hmm [yes], mm-hmm [yes]. So let’s get back to Yale.

Casten:

Okay.

Zierler:

Did you take on graduate students beyond the laboratory, or all of your graduate students were part of the lab?

Casten:

I’ve got to try to think what that means.

Zierler:

In other words, did you have graduate students just in your capacity as a professor of physics who were not associated with the lab?

Casten:

Are you making a distinction between the department and the lab?

Zierler:

Right.

Casten:

Oh no, no. They were all graduate students in the department who worked at the lab.

Zierler:

Okay.

Casten:

My wife just said in the background, “Burcu.” Yeah, one exception.

Zierler:

[Chuckles] So she has been listening!

Casten:

I guess so, yeah. So I want to mention another graduate student while I was at Brookhaven. I mentioned Jolie Cizewski. There was another one, Ani Aprahamian. She was a student of an excellent scientist Daeg Brenner at Clark University. He and I have worked together from the early 1980s for about 30 years. Anyway, Ani is now a professor at Notre Dame and also Director of the nuclear physics institute in Yerevan, Armenia. So she did work with me at Brookhaven in the mid-’80s. She played a major role in developing the idea of multi-phonon states in vibrational nuclei.

Zierler:

Rick, I’m curious. You were out of an academic environment for so long. Did you embrace the teaching responsibilities when you got back to Yale? Was that something you were looking forward to getting back into?

Casten:

I have always been interested in teaching, and in fact, long before I went to Yale, I wrote a textbook, Nuclear Structure from a Simple Perspective. Maybe you saw it on my CV or something. That was in 1990. If you ever decide to read it, which you won't, read the 2000 edition because the 1990 one is riddled with errors. Anyway, and I had given lectures. I gave a course at Drexel. I had always been interested in teaching. So in fact, that was one of the things that was appealing at Yale, that I could do that. But anyway, at Yale, the graduate students with one exception… Sorry. What, JoAnn? JOANN: You gave lectures in China.

Casten:

Yeah, I gave lectures in China and so on. Yeah, the students were in the department with one exception. Well, probably others, but one main one. One was a woman named Burcu Cakirli who’s from Istanbul, and she came… She was never formally associated with Yale, but she spent several visits, six months or so at Yale and got her thesis, her PhD at Istanbul University. I was her official thesis advisor. In fact, I went to her thesis defense which was in Turkish and even asked a question in Turkish.

Zierler:

Wow!

Casten:

I had no idea what the answer was. [Laughter] She and I still work together every single day. She is extremely smart and has had a number of great ideas, especially regarding the p-n interaction and its relation to nuclear masses. A few years ago she won the IUPAP Best Young Scientist in the World Award.

Zierler:

Oh, wow.

Casten:

I’ve already emailed her twice today. With my wife, Jo Ann, we have also traveled all over Turkey.

Zierler:

Rick, I’m curious. Did you—

Casten:

But there’s one other feature [?] of my graduate students maybe you don't know.

Zierler:

Please.

Casten:

Only one was male.

Zierler:

Yeah, I noticed that.

Casten:

Yeah, okay.

Zierler:

You want to comment on that, what that means?

Casten:

[Laughs] I don't know! Jolie Cizewski was the first and Ani Aprahamian. I don't know. There’s Libby McCutchan, who is now at the Nuclear Data Center at Brookhaven. Mark Caprio is the male. He’s a professor at Notre Dame. Burcu Cakirli is a professor at Istanbul University. Deseree Meyer who was jointly a student of me and Con Beausang. She had the best native intuition about nuclei of any student I ever encountered. I’ve probably forgotten some. Yeah, so I don't know how it happened. It just happened. Well, I think one way it happened was once I had one or two female graduate students, word got around that it wasn’t so bad working with me, I guess. You know, word of mouth, I guess. Plus a lot of female post-docs and visitors, working in the lab, often but not always directly with me. Others, visitors or Post-docs included Jo Ressler, Andrea Jungclaus, Astrid Gollwitzer, Lissa Zyromski, Lidya Amon, Hannah Amro, Liz Williams, etc. Lots of female undergraduates too. I remember one Nuclear Structure Group photo we had in the 2000’s with about 30 people and the majority were female. One thing I am very proud of is that all my PhD students have gone on to excellent, leadership careers, either at Universities or National Labs.

Zierler:

I’m curious, Rick. Did you see the directorship at WNSL as an opportunity to change some of your research, or was it an opportunity to expand on what you were already doing?

Casten:

No, it was basically a complete change because I had been working at Brookhaven on a reactor, which is a faucet for neutrons, and at Yale it was charged particles, accelerator physics. So the research physics, the themes were very, very similar, but the techniques were totally different.

Zierler:

In what way?

Casten:

Well, it was using accelerated beams of ions and colliding them with nuclei and looking at nuclear reactions, whereas at Brookhaven it was just dropping neutrons into nuclei. The instrumentation at Yale was different because as a product of these reactions, a lot of charged particles come out, and so you have to detect charged particles, either other nuclei or protons or whatever, whereas at Brookhaven it was all neutron falls in and only gamma rays come out. So the techniques were different. Physics was very similar.

Zierler:

What undergraduate types of classes did you teach?

Casten:

Well, let me get a graduate one out of the way. The main graduate course I taught was a nuclear structure course. I taught for a bunch of years, and that was basically out of my textbook. Undergraduates I taught… Well, this won't be complete, but it will be the two main ones. I taught a lab for premeds, which for the most part they hated. We tried to make it interesting. That was a lab for like 200 students. It got better as the years went on. It went from 140 students up to 200 because it actually attracted some students, but that was a required course for them which they just wanted to get through mostly. It was satisfying in the sense that I think we improved it in ways that made it more relevant to their lives, their careers, but it was frustrating also because they basically weren't interested in it. But then the main thing—

Zierler:

What would you need to teach? What was important for a premed to understand about physics?

Casten:

Well, the only science is physics. The rest is applications. But I didn't invent that phrase. I think Einstein said it.

Zierler:

Yeah.

Casten:

So anything you want to know about the body is, at the first level, chemistry, but chemistry is just physics. So understanding principles of physics is important. In my opinion, those courses are taught in a completely wrong way with wrong emphasis. The students tend to forget what they’ve learned instantly after they’ve completed the requirement. They sort of are done as watered-down physics courses with levers and pulleys and optics and stuff that has very little relation to medicine. I think you can make it much more interesting, and we tried and succeeded a little bit. Okay. The other course I taught, which is the one I’m very excited about, was called physics in the world around us. It was for an… There were two prerequisites. One was you had to be a non-science major, and the other is you had to be able to add, subtract, multiply, and divide with a calculator. That’s it.

Zierler:

Okay.

Casten:

And it was not a watered-down physics course, not at all. What it did was do two things. It had two approaches. One was to take some area of activity like sports and talk about the physics of sports, and in many cases showing how the same physics principles appear in racing, sailing, football, baseball, tennis, Frisbees, all that sort of stuff. By the way, you know the Frisbee was invented in New Haven?

Zierler:

I think I might have heard that somewhere. [Laughs]

Casten:

Mrs. Frisbee. She made pies for the students in the ’20s out of pie tins.

Zierler:

There you go!

Casten:

So that was one theme. Take an activity and look at everything…how physics comes in there. The other was to take a physics concept like conservation of angular momentum, which sounds very esoteric, and show how it comes in all sorts of daily life areas. Example. When an ice skater brings in their arms, they spin faster.

Zierler:

Right.

Casten:

Angular momentum has to do with how fast something is rotating, but also how far out from the center it’s rotating. So if you have an ice skater with her arms way out, you have the same angular momentum rotating slowly. If they bring their arms in, to keep the same amount of angular momentum they have to rotate faster. Okay? When a diver does a tuck, a high diver, and they rotate, that’s conserving angular momentum. Then when they want to go in the water, they un-rotate; they stretch their bodies out and stop rotating. So all these things. So those were the two themes, and the course was so much fun. I actually designed it… The year before I gave it, I had a group of undergraduate students in theater arts and philosophy and whatever help me design the course and what they would like to hear. Then I taught it for two years before I retired, and it was so much fun. We had about 40 students. Could have had 150. The sign-ups were…but I insisted on limiting it. We would have demonstrations almost every day. There were lots of questions. One of the themes of almost every lecture I give to students is the acronym TINSTAASQ: There Is No Such Thing As A Stupid Question, and I put that on the first slide always.

Zierler:

Oh, very nice.

Casten:

Anyway, I really stressed that with this course, and in a 75-minute lecture I would typically get about 40 questions. Sometimes I’d go off the topic I wanted to talk about originally; the question was interesting. It was very interactive. I’m going to ask you a question now.

Zierler:

Please!

Casten:

90% of the questions were by one group of people and 10% by the other. What are the two groups?

Zierler:

The 90% are the men who asked questions.

Casten:

90% are the women.

Zierler:

Really!

Casten:

Yes.

Zierler:

Wow! Good for them.

Casten:

I actually brought this up in class and we discussed it as to why.

Zierler:

I mean my assumption would be that men just feel less shy in those sort of circumstances, but I guess I’m wrong.

Casten:

I don't know the answer, either. One theory (and I have no idea if it’s right) is that a number of the men were in athletics, and they might have been embarrassed at asking a stupid question.

Zierler:

Oh, I see.

Casten:

I don't know jock culture. I don't know, but in any case, 90% of the questions were by the women. To this day, which is now five years later, I still see some of the students, Kate Wiener, Rachel O’Driscoll, Alina Aksiyote, Daisy Wolf. We have coffee or lunch or something in New York, and those are all the women. They’re beginning to spread out over the country, so it’s a little harder, but anyway, I loved teaching that course. We went so much further… So we developed the syllabus the year before the course, and what we covered was so much more. I mean we got into quantum theory. We got into relativity, quantum entanglement, astrophysics, applications, PET scans, things like that—all sorts of things. It was just so much fun.

Zierler:

Rick, were you ever able to convert any of those students into becoming physics majors?

Casten:

No, but I didn't want to. I wanted them to be physics… Now I’ve got the wrong adjective.

Zierler:

Physics literate.

Casten:

Physics literate non-scientists. I thought that was more important. They were just so good. I mean it was amazing.

Zierler:

Yeah, yeah.

Casten:

The questions they asked… I mean, of course there were some questions which you might call stupid, but they were really good.

Zierler:

Was it partly for this course that you won the DNP Mentoring Award in 2009?

Casten:

No. I won the Mentoring Award for my female graduate students.

Zierler:

Oh.

Casten:

I think… That sounds like you don't have access to the citation words because I think it said that.

Zierler:

Oh, it did. I’m working off your CV.

Casten:

Oh. Maybe I should have put that in. Anyway, yeah. No, that was for female graduate students.

Zierler:

What did it feel like when you were named the Bromley Chair?

Casten:

Cool!

Zierler:

Yeah?

Casten:

[Laughs] Yeah! I mean I thought it was a tremendous honor.

Zierler:

Were you the first?

Casten:

I was the first one because you have to be dead to have a chair named after you, and Bromley died in 2005.

Zierler:

Did his family fund it or was it from the University?

Casten:

No, it was funded by… Bromley over the years had gotten some donations—I’ve got to say I hope this right; I’m not 100% sure—from donors who wanted to support his physics. This money, there was some sort of conflict about whether this money was his—I don't mean his personal money, but for the lab or whether it belonged to the University—and I’m really not sure about this. But in the end, I think the compromise was to make the Bromley Chair, so use the money to help the University, but it would be involved with him.

Zierler:

You decided to step down from the lab seven years before you became emeritus. I’m curious why.

Casten:

Oh, boy. Now you're getting into a very touchy subject. Since this is potentially public, I’ve got to be a little careful what I say.

Zierler:

And remember, you can always edit as you want for the transcript.

Casten:

I’ll give you a toned down, slightly expurgated version of it. There had long been some antipathy to the lab in the rest of the department.

Zierler:

In the physics department!

Casten:

Yes, which stemmed from…

Zierler:

Resources?

Casten:

No, no. It was more… Oh, god. I’ve got to be careful what I say. There were people in the department who did not like Bromley or the lab. This morphed into a dislike of nuclear physics, even after Bromley had no connections with the lab.

Zierler:

You mean to tell me that interpersonal conflicts bled into questions of the validity of even subfields in physics?

Casten:

Can you imagine that?

Zierler:

[Laughs] It seems a bit petty.

Casten:

No comment. In any case, over the years they did not give tenure to any of the junior faculty.

Zierler:

In nuclear physics.

Casten:

I… Let me say this. In faculty votes relating to tenure for junior faculty, they did not get tenure.

Zierler:

And you're saying for reasons that go beyond their academic potential and accomplishments.

Casten:

I’m saying because there were people in the department who did not think nuclear physics was a frontier area.

Zierler:

Okay.

Casten:

I’m trying to be very careful here.

Zierler:

Okay.

Casten:

In the end, there were no tenured appointments—aside from me and Peter Parker who was there, but he wasn’t that active—available to work at the lab. DOE has a rule that for a major lab facility, there have to be at least two active, tenured researchers, and when the last junior faculty member didn't get tenure—I think that was Reiner Kruecken, or maybe he left because he knew he wouldn't get tenure. I’m not sure of the exact chronology. No, no. Wait a minute. Wait a minute. Hang on. Okay, yeah. No, sorry. Sorry. I’ve got to get this straight. So the junior faculty didn't get tenure. At some point there was a search for a new faculty member and we had a candidate. The candidate got great letters of reference but in the end wasn’t given an appointment. It was clear that there were not going to be any tenured appointments at the lab, and the lab couldn't survive. We also discussed possible senior appointments and one candidate is, I would say, in the top 10 of any list of the best nuclear structure /reaction physicists in the country, maybe the world, and a major Prize winner, and is a major lab director now, and the other is also now a lab director. They were not considered good enough. This was so silly and, in my opinion, not reality-based. There was no more I could do since new appointments became impossible. So I resigned.

Zierler:

Rick, I’m curious. Do you think that Yale’s attitude towards nuclear physics accorded with the general attitude in the academic physics community at large towards nuclear physics?

Casten:

No.

Zierler:

Or was Yale an outlier?

Casten:

Nuclear physics has a number of subfields, as you know. Low energy nuclear structure, nuclear reactions, nuclear astrophysics is one. That’s the area that Yale is involved in, or was. Other areas are RHIC physics, JLab physics. You know about that.

Zierler:

I do.

Casten:

Okay. Neutrino physics. These are all different subfields. The area of nuclear structure and reactions, “Yale area,” is in fact the major growth area in nuclear physics. It’s the area where RIKEN, GSI-FAIR, FRIB, these exotic beam facilities for rare isotopes—those are all billion-dollar facilities that are being built around the world and it is the growth area. The next growth area in 2030 or so will probably be an electron-ion collider, which I’m sure you’ve heard about.

Zierler:

Yeah.

Casten:

But currently… And neutrino physics is growing, but it’s still a tiny percentage compared to nuclear structure and reactions. So structure and reactions are the growth area in nuclear physics. But the people at Yale who didn't think there should be tenured faculty appointments at the tandem. They didn't have problems with areas like neutrino physics which were not associated with the kind of physics done at the tandem. So they did hire a guy, an excellent guy named Karsten Heeger, who is now running the Wright Lab. He’s in neutrino physics. The accelerator has been torn up and chopped up into pieces and gone. They have no problem with that kind of nuclear physics. So it’s really nuclear structure, nuclear reactions, astrophysics that they didn't think were a frontier area, but in fact, that is the growth area in the field worldwide by far.

Zierler:

So to be clear, Yale, in its approach to nuclear physics, is like comparable departments elsewhere in the country, or it’s not?

Casten:

No, no, no. I mean, Yale is now doing neutrino physics, dark matter searches, that kind of stuff, which is a growing area, still relatively small. I don't know the percentage of the DOE budget. Up until a few years ago, it was about 3%, whereas nuclear structure and reactions, astrophysics was like 25% or something like that. That’s growing, but still the dominant area is nuclear structure, reactions, astrophysics. The physics done at FRIB, done at Michigan State’s current facility, the National Superconducting Cyclotron lab - NSCL, and Berkeley and Oak Ridge and other facilities. That’s the major area. Let me put it this way. I’m an editor for Phys Rev C for low energy nuclear experiments. Excuse me. Nuclear structure and nuclear reactions. That area gets the most submissions of any area, okay—so much so they had to hire another editor in that area to cover it. So it’s the major area. There are other areas like neutrino physics that are growing, but nuclear structure, reactions, study of exotic nuclei will dominate for 20 years.

Zierler:

Rick, I’m curious—and again, knowing that you can fully edit the transcript once you see it, did you see your resignation as having a potentially positive result? In other words, is this the kind of move that can have an impact to shake people up and to, you know, hopefully get people to think in new ways that, long-term, would be for the better in terms of the lab and its future?

Casten:

No.

Zierler:

Or was it simply you were fed up and you wanted to be out?

Casten:

Pretty much the latter. Let me give you a little more history. The day I… So when they were recruiting me for Yale, I had a meeting with the provost.

Zierler:

Surely you knew. I mean, you were a student of his. You knew the backstory with Bromley. You knew his relationship with the department. This was not news to you.

Casten:

No… Maybe the depth of the distaste was news. But anyway, when I interviewed with the dean at Yale prior to them giving me an offer, the dean said to me, “While we’re very excited to have you come, what are your plans for closing the tandem?”

Zierler:

Yeah.

Casten:

This was ’95.

Zierler:

This did not sit well with you, I assume.

Casten:

I said, “Well…” Well, in some sense the question was reasonable because the tandem wasn’t doing anything. The research program was really moribund. I wonder if I’ve ever said that word orally in my life. Anyway. It was moribund.

Zierler:

[Laughs] Never too late for a moribund reference.

Casten:

Hold on. I’m getting a note. Yeah, I’ve already done that, JoAnn. She’s giving me advice. Okay. So I said something like, “Well, we’ll see how the program develops over the next few years.” Okay. And in fact, when I came there, I made a deal with DOE. The deal with DOE was… I mean, they were going to close the lab. The deal with DOE was they would give me a two-year grace period to try to develop the program.

Zierler:

I don't understand. How was this that they’re recruiting you and they planned to close the lab at the same time? I thought they were recruiting you for the lab.

Casten:

Well, also for a faculty position, so they didn't mind having me as a faculty member.

Zierler:

But your main draw was for the lab. I mean, you could have been a faculty member at a lot of places.

Casten:

I don't know the answer. I don't know the answer. But anyway, I made this deal with DOE for two years, and I think this dean was hoping that that would do it. But we persisted and I was director for 13 years and the lab kind of lingered on for a few years. But it was a tooth-and-nail fight the entire time. Originally I think some members of the faculty were hoping that the fight would last these two years and be over, but we kept doing well, to be honest. I mean, Yale’s rankings in the various… like US News & World Report went from like 10th to 13th or 14th during this time, and the tandem went from like…the nuclear physics went from like 9th to 5th. So we argued that we’re actually helping the department’s rankings, but none of that carried much weight when it came to votes. So it was a constant, constant struggle, and when it finally became clear that they were not going to vote in support of any tenured position, there was just nothing more to do. So fed up, gave up is the answer, really. There was nothing more I could do. I had held off for 15 years.

Zierler:

What was the practical effect after everybody cooled down when you resigned? What happened as a result?

Casten:

Well, they appointed other directors, some of whom were caretakers. The first one was kind of a caretaker. Then they put John Harris as director, but his field is relativistic heavy ions. He works at RHIC and CERN. That was always part of… Oh, I should be careful. WNSL was not just low energy nuclear physics. It also had this relativistic heavy ion group—John Harris, Helen Caines, and others—and they were an integral part of the lab. They didn't use the tandem. They did physics at RHIC. They did physics at CERN and so on. So after a year, John Harris became director and maintained the tandem work at some level. His personal interest was relativistic heavy ions. They didn't hire anybody new, and then after a while—I can't remember if there was another interim director—they hired Karsten Heeger, who came from Wisconsin in neutrino physics. With that, they just dismantled everything, renovated the lab, took out the accelerator, took out all the instruments.

Zierler:

I’m curious if your affiliation with Michigan State, if that was sort of a smooth landing from retiring from Yale, if you saw it sequentially.

Casten:

I’m not quite sure what you mean. Let me say something about my affiliation with Michigan State. I’m on a very small percentage salary and I’m there about ten days a year.

Zierler:

I was asking—

Casten:

My job—

Zierler:

I was asking—Please.

Casten:

My job is to be a kind of consultant to make FRIB and its capabilities known around the world because I travel a lot, or at least I did up until March—like a roving ambassador or something like that. So it’s not a normal position.

Zierler:

No, right. But what I meant was did you see FRIB as a way for you to pull back from your full-time responsibilities, but to maintain engagement in the field as you had transitioned to emeritus?

Casten:

Not in the sense you mean. Obviously I maintain some engagement, but no, my remaining engagement in the field is just based on my research…

Zierler:

Right, right.

Casten:

…which is not at FRIB, because it doesn't exist yet, although I’ve been promised I’ll be on the first experiment. There’s a part of that we should probably discuss at some point. Anyway, no. My engagement in the field is through my research, which is—

Zierler:

Right, right. What would you like to discuss? You said there’s a part of that that you wanted to discuss.

Casten:

Oh. So this whole business about exotic beam facilities, that was a major part of my life. I was one of nine founders of a group called the ISL Steering Committee in 1989. You probably don't know that acronym.

Zierler:

No.

Casten:

It stands for IsoSpin Laboratory. Isospin is a fancy way of saying the difference in the number of neutrons and protons in the nucleus. So if you go far off stability, you either minimize isospin if you get nuclei that are almost equal numbers of protons and neutrons. That’s called the proton-rich side; relatively you have fewer neutrons—or the neutron-rich side, which is the main area of study, okay, the isospin is large. So isospin was a way of saying making nuclei with unusual combinations of numbers of protons and neutrons. That committee was formed to promote the idea of building one of these multi-hundred-million-dollar facilities. We started in ’89. After 10 or 15 years, the acronym ISL got replaced by RIA, which is Rare Isotope Accelerator, and then that became FRIB. So from 1989 until 2000-and-something, 2009 maybe—you can check my CV—I was chair of that committee. That was probably the major committee, major group of people promoting this field and organizing workshops and writing white papers and so on. It took a long time to get FRIB approved and funded. I worked a lot on this with Brad Sherrill, Witek Nazarewicz, and Robert Janssens – we jokingly called ourselves The Gang of Four. Finally the decision was made to go forward with the facility. Then after that, I was chair of the FRIB—I don't remember the official name—FRIB Science Advisory Committee or something from 2009 to 2014 or so. So I played a role in the worldwide effort for radioactive beam facilities. I was also chair of a committee at GSI-FAIR for their facility and so on. Anyway, so that was a big part of my life for 30 years. I mean it’s taken 30 years since 1989, and it was 20 years before it really got approved.

Zierler:

Do you see that as integrated with your overall research agenda or—?

Casten:

Absolutely, absolutely because the physics I study, the best place to study it is in exotic nuclei off the line of stability, off the valley of stability.

Zierler:

So I’m curious. Best-case scenario, once FRIB comes online, what are you hoping it will achieve?

Casten:

It will be, by far, the world’s best facility of its kind. It will have access to gazillions of new nuclei. Nobody wants to study all of them. It’s not… It’s not… What’s the phrase? I can't remember the phrase. It’s not just doing every nucleus because it’s not studying linoleum and then… It’s not just trying to study every possible nucleus. It’s trying to pick those nuclei and those aspects of them that will teach us new physics, and much of that physics is intimately tied up with this whole theme of individual particle motion and collective motion and looking at correlations of observables. (Other aspects are related to astrophysics, so-called, fundamental physics, nuclear reactions, etc.) One of the main things I’ve done throughout my whole career is look at correlations of observables. You know what I mean by an observable?

Zierler:

Yeah, sure.

Casten:

Okay. So taking some facet of nuclei like the energy, the first excited state, and taking another facet like the number of neutrons or the product of the number of valence neutrons and protons, or the energy of the first 4+ state and plot one of them against the other, you see amazing things.

Zierler:

In what way, Rick, will… Can you explain how all of these new nuclei will be seen? Is it a matter of more powerful instrumentation? Is that what this is about?

Casten:

It’s this triple revolution that I referred to before—the ability to accelerate the nuclei, to make them and to accelerate; the ability to use instruments that are a billion times (or 100 million times) more sensitive than when I was a student to study them, get data on them; the ability of computers to deal with the data online as it comes in; and the ability of computers to do the theory. So it’s a combination of all those things. The benchmarks of nuclear structure since the ’50s, since ’49 were the so-called magic numbers. Do you know about those?

Zierler:

No.

Casten:

Oh. Oh! Okay. Remind me to say something about history and archeology.

Zierler:

[Chuckles] Okay.

Casten:

Do you know about inert atoms like the noble gases like helium?

Zierler:

Sure. Yeah.

Casten:

What’s special about those, the reason they are inert is they have certain numbers of electrons whizzing around the outside that form what are called closed shells. You can't add anymore, and the next electron is added at a much larger radius. Nuclei have exactly the same thing, okay, and they’re called magic numbers. Nuclei with those numbers of nucleons have special properties, and they divide the whole nuclear chart into these segments in between the magic numbers. The magic numbers are different than those in atomic physics. They’re 2, 8, 20, 28, 50, 82, 126, and so on. Those have been hallowed, cherished benchmarks of nuclear structure from 1949 when Maria Goeppert Mayer and Haxel, Jensen, and Suess got Nobel Prizes. Well, Jensen and Mayer got it, but those two pieces of work. . Those magic numbers were invented or deduced or discovered because of the properties of nuclei that are stable or near stable because those were the only ones that could be studied.

Zierler:

Okay.

Casten:

As we go off stability, those magic numbers turn out to be fragile and they break down. New ones come up, and this is due to interactions amongst the valence protons and neutrons that change the structure of the nucleus. So that’s led to entirely new theoretical developments to try to explain this fragility and evanescence of the magic numbers. When you have a nucleus that does not have a magic number of protons and neutrons, you get these collective effects. So it’s all tied up and so the exotic beam stuff is trying to study how that all evolves. That clear?

Zierler:

That is.

Casten:

I want to show you one… Can I share the screen for a second?

Zierler:

Certainly.

Casten:

Where’s the zoom thing? Share screen. Share… Do you see a river?

Zierler:

I do.

Casten:

Okay. So those are wildebeests crossing the Mara River in Tanzania and Kenya, and that’s an example… Let me make it bigger. That’s an example of single particle and collective motion, okay? All these guys are individual wildebeests, and yet they go across in tens of thousands. Okay?

Zierler:

Mm-hmm [yes].

Casten:

Let me get rid of that and show you what I really wanted to show, but I found that first. Why can't I find it? [Looking] Here. Okay. Can you see the cursor?

Zierler:

I can.

Casten:

Okay. So these are the first couple of energy levels of a typical nucleus. If I plot the energy of this level against neutron number, I get this plot, which has some trends, but you’d have to say it’s complicated, right?

Zierler:

Looks… Yeah, right.

Casten:

If instead I plot the energy of this state against the energy of this state, these same data look like this. It’s exactly the same data, and this, I guess you’ll agree, is simple.

Zierler:

Right, sure. It’s a line.

Casten:

And it has two parts to it. It has a segment here that has a slope of 3.33 and a long segment here with a slope of 2.00. Those two numbers are very important numbers. A nucleus which is deformed and non-spherical, the energy levels will have exactly that ratio, and many other nuclei have exactly this ratio. So plotting one observable against another, thinking out of the box—whoops. Thinking out of the box has been a major part of my research, okay? So that’s one point I want to make. The other is you have to be very careful about these correlations. You can get accidental correlations, false ones, and here’s an example. Can you see that?

Zierler:

I can.

Casten:

Lobsters for rent. That’s a false correlation. A fish store went out of business. They put a “for rent” sign just below the word “lobsters” which they used to sell. By the way, that was just near Brookhaven when I went out shopping. Then I found other false correlations, so take a look at this. Worldwide non-commercial space launches; sociology doctorates awarded. Beautiful correlation. Crude oil imports… Can you see these?

Zierler:

Yeah.

Casten:

Crude oil imports from Norway; drivers killed in collisions with railroad trains. Number of people drowned by falling into a pool; number of films Nicolas Cage appeared in, and it goes on and on and on. So one also has to be aware of false correlations. Oh, I’m still sharing the screen, right?

Zierler:

I see the Chihuahua.

Casten:

Yeah, that’s Sassy.

Zierler:

Hello, Sassy.

Casten:

Unfortunately, she died.

Zierler:

Oh.

Casten:

All right. So I don't even remember any longer why I wanted to show you that, but looking at correlations of different observables has been a key part of my research.

Zierler:

The other thing that you wanted me to—

Casten:

That will be enhanced by looking at more and more nuclei and getting more data.

Zierler:

I see. Oh, and this gets back to at Michigan State you’ll be able to see these things. Right.

Casten:

Right.

Zierler:

Rick, the other thing you wanted me to remind you to talk about history and archeology.

Casten:

Oh. And geology also.

Zierler:

Sure.

Casten:

Just because we’re talking about me, one of my main interests always has been history, geology, archeology, and… If I weren't a person, I’d like to come back in my next life as a glacier, just as an example. What was your major?

Zierler:

History.

Casten:

History. Does Çatalhöyük mean anything to you?

Zierler:

No. What is that?

Casten:

That was a city in Turkey built in about 7000 BC.

Zierler:

Okay. Not my area.

Casten:

Okay. What was your area?

Zierler:

Biology in the Vietnam War in the ’60s.

Casten:

Oh, okay. That’s not history. That’s current events!

Zierler:

[Laughs]

Casten:

In any case, so I’ve always had an interest in history and geology, archeology. I don't know why I’m saying that, but… Oh yeah, I know one other thing. So I talked about looking at data from different perspectives. It would be nice if people did that in daily life. People tend to look at things only from one perspective, and one nice example of that is does the date 1453 mean something to you?

Zierler:

I want to say something with Constantinople, but… Yeah?

Casten:

The fall of Constantinople.

Zierler:

Oh, wow. Okay.

Casten:

If you go to Istanbul, they also know about 1453. It’s the date of the liberation of Constantinople. Different perspectives.

Zierler:

Different perspective.

Casten:

Yeah.

Zierler:

And you feel like a life in physics has enhanced your ability to appreciate different perspectives.

Casten:

No, I think my ability to appreciate different perspectives has enhanced my physics.

Zierler:

Ah! The other way. The other way.

Casten:

Yeah. Yeah.

Zierler:

Rick, I want to ask you, for the last portion of our discussion, a few sort of broadly retrospective questions. The first is when I talk to particle physicists, they talk about the golden age in particle physics which sort of ended in the late 1970s and early 1980s, and there are lots of ideas about why that was and what it might take to get into a second golden age. Do you see in nuclear physics those similar kinds of peaks and valleys?

Casten:

Absolutely.

Zierler:

What are they, over the course of your career?

Casten:

Okay. You actually can figure that out from what we’ve said. The late ’50s— Well, let’s say the early ’60s…or let’s say the ’60s were one giant peak when these new tandem accelerators, germanium detectors, computers… Yale, by the way, in the ’60s was the first lab to have some of the processes controlled by a computer. So that was one peak where nuclear physics really made a giant leap forward.

Zierler:

And obviously you rode that peak as a student.

Casten:

Well, yeah. I was a small part of it. Okay. Then that continued into the ’70s, and then into the ’80s it began to tail off. There was an area of nuclear physics called high spin physics, which was very important, a lot of interesting discoveries in the ’70s. It continued into the ’80s but began to be a little bit more the same, wifnium, wafnium, and so on. Also, as you got toward the late ’80s, we kind of knew what we wanted to measure, but didn't have the technology for it. What’s that? What’s that noise?

Zierler:

A helicopter.

Casten:

Oh. We didn't have the technical ability to do it and we ran up against a technological wall. I’m talking about my area of nuclear physics.

Zierler:

Right.

Casten:

What broke through that wall was the exotic beam era, these accelerators that can make and accelerate and study exotic nuclei, and so now we’re in another peak. So if I were to graph it from your perspective, this being early—here’s the ’50s. Here’s the ’60s. Here’s the ’70s. Here’s the ’80s. Here’s the ’90s and then… Oh, I’m off-scale. And then way up now and it will be flat for a while at the top.

Zierler:

So exotic beams is really the future.

Casten:

For my area, yeah. I give a series of lectures at Michigan State as part of this consultant thing, and one thing I typically tell the students, that the two times when it was probably best to be a graduate student in nuclear physics, if you were lucky, was the ’60s and now.

Zierler:

That begs the question, you know, you were an advisor, a mentor to graduate students for the bulk of your career in between those two peaks. So what advice have you given to your graduate students in terms of navigating the field where it was at that time?

Casten:

There were always lots of exciting questions, so an individual person could always do exciting research. But the field as a whole was running into some troubles in the late ’80s. Well, I had a student in the late ’70s, a student in the early ’80s, and then I really didn't have a student until the late ’90s when we were going up again.

Zierler:

Mm-hmm [yes], right.

Casten:

And symmetries, which is correlations—single particle, collective motion symmetries have been the main themes. Symmetries throughout this whole period was a very active area. That’s what I won the Bonner Prize for, my work on symmetries, which, in that context, is a code word for interacting boson model. And much of the content of the 2002 Tetons conference held for my 60th birthday out west also focused on symmetries, geometrical models of the nucleus, correlations of observables, and the like.

Zierler:

You touched on this a little bit throughout our talk, but I wonder if you could answer more directly. What do you think it was that led to this new development in beams where you see now is this new golden age for nuclear physics? What kinds of advances in both technology and thinking that allowed for these new beams to come into existence?

Casten:

Okay, I think I’ve answered that. It’s what I call this triple revolution. The accelerator technology that allowed us—I say “us,” but it’s really the accelerator people—to produce beams of nuclei that could collide with stable nuclei and make exotic nuclei, and then the ability to extract those exotic nuclei and use them for experiments, so where the new projectiles, if you want, were the exotic nuclei, okay? So that’s one thing.

Zierler:

Right.

Casten:

We can do that, but the numbers of those exotic nuclei are typically in the hundreds or thousands per second compared to a billion per second with stable nuclei. So unless you develop very specialized, highly sensitive instruments, you're not going to be able to take advantage of that. So the second part is the instruments. The third part is computers to control these processes and to analyze the data event by event as it comes in. Then the fourth part of the triple revolution [chuckling]—sounds like Yogi Berra. Baseball is 90% mental and the other half is physical. The fourth part of the triple revolution is using these advanced computers for nuclear theory to really advance our understanding of nuclei using complex models that you could never even have approached before. In fact, there are kind of two realms—no, realms is not the right word—two facets of nuclear theory these days. One, which has become the dominant… No, let me go back. Throughout much of the last half-century, the dominant approaches to nuclear theory have been simple models that you could do on a very simple computer or even with a calculator, so-called phenomenological models (although that has a bad connotation these days) based on symmetries, things like that. And then starting 10, 20 years ago, more detailed microscopic theories that used advanced computing. These have been the two themes, and in fact, if you look back at the long-range plans for DOE and NSF for nuclear physics, at the beginning of any discussion of the nuclear structure part of the chapter, you’ll almost always see these two aspects, microscopic and macroscopic, looking at the interactions of the individual particles in the nucleus, or looking at the nucleus as a whole, okay. These have been the two dominant themes. In the last 15 to 20 years, the latter, the detailed microscopic work, has come to the fore and dominates now, and that’s dependent on advanced computing.

Zierler:

So you really see technology as the main driver of this revolution in nuclear physics.

Casten:

I’m not particularly technologically oriented. I’m more physics oriented, so it hurts me a little to say it, but yes.

Zierler:

Rick, I’m curious if you see your work or the work of nuclear physics in general as contributing to these broader existential drives in physics towards unifying the whole field in one theory. Do you see your work or the field of nuclear physics as contributing to those efforts?

Casten:

Not so much the part that I’m involved in. What they call the neutrino sector… I mean, this is relating to the standard model and what goes beyond the standard model, and that’s related to neutrinos, neutrino masses, neutrino hierarchies. I don't know if you know these terms.

Zierler:

Yeah.

Casten:

And dark matter. I personally don't like dark matter and dark energy because before them, nuclei were 99% of the matter in the universe. Now they’re 4%.

Zierler:

[Laughs] What a downgrade!

Casten:

I would like dark energy to go away, but okay. Those are the areas that are more related to these grand unification kinds of efforts. I take that back a little. One part of low energy nuclear structure, nuclear reactions is nuclear astrophysics, and that is related to it—the origin of the elements, nucleosynthesis, supernovae, stuff like that. In fact, that’s what I’m doing nowadays in large part. But that’s related to basically the overall structure of the universe and the origin of the elements.

Zierler:

Well, Rick, now that we’ve worked up to the present day, I think for my last question to wrap up this terrific time I’ve had with you, it’s a forward-looking question, and of course it relates to the fact that physicists never retire, right? They just keep on going and going and going. So I’m curious. As you look ahead for the rest of your career, what are the things that you are looking forward to accomplishing? What are the things that excite you about this new revolution in nuclear physics, and what do you see as your contributions as you remain active in the field?

Casten:

Okay. Part of my activity is being an editor for Phys Rev C, but that’s sort of on the side. The stuff I’m doing currently is basically two things. One is studying the r process. Is that something you know about?

Zierler:

No.

Casten:

Oh my god. [Laughs]

Zierler:

But even if I don't, for the benefit of our readers, they should know what the r process is.

Casten:

All right. Most of the elements except for hydrogen, helium, and a little bit of lithium are made in stars. Stars are powered by nuclear reactions, not by mice on treadmills.

Zierler:

Okay, good. Good.

Casten:

These nuclear reactions lead to the production of sequentially heavier and heavier nuclei—alpha particles, carbon, oxygen, neon, magnesium, on and on and up—up until iron. Okay? The reason that that happens is because if you have enough energy, enough temperature in the star to make these ions, these nuclei move fast enough, they can overcome the Coulomb barrier and fuse and make heavier nuclei. So you go alpha, carbon, oxygen, and so on.

Zierler:

Yeah.

Casten:

Each one of these successive nuclei is more and more bound than the others, so once you make them, you’ve got them. When you get to iron, after iron nuclei tend to become less bound. If you want to see that, look at Figure 1 or Figure 2 of my textbook and you’ll see a figure showing the amount of binding per nucleon as a function of nucleon number. I’ll do the graph for you. It goes up sharply, plateaus, and then basically stays constant, declining slightly, and the peak is at iron. Once you get beyond iron, you can't make the nuclei that way because if you fuse them, they won't be as bound as what you started with. So the way to make all the elements’ isotopes beyond iron is to capture neutrons. You capture a neutron; you make a heavier nucleus, heavier, heavier, heavier. Finally you capture enough neutrons that they drip out over the surface. They’re no longer bound, and then that nucleus sits there and beta decays to a nucleus with one more proton, which could then accommodate a few more neutrons. So you march up the chart of the nuclides. So understanding the origin of the elements beyond iron is largely a question of understanding the r process. R stands for rapid neutron capture. This happens in supernovae where you have incredible densities of neutrons, like 1024 per cubic centimeter. The nuclei capture a neutron and before they can decay, they capture another one, and so it just marches up the chart of the nuclides. Okay, so lately I’ve been studying that process. We have some new ideas about how to understand the neutron capture process that are much, much simpler. They replace models with 20 parameters with parameter-free correlations. So we’re kind of excited about that. The other thing I’m doing is working on developing new signatures of structure using simple data. With these exotic beam machines, we’re able to study new nuclei, but we’ll never get the kind of data we got on a stable nucleus in the ’60s. So we’ve got to learn to enhance also the efficiency of our signatures of structure, getting physics information from fewer amounts of data. That involves developing new signatures, looking at new observables in different ways, and so that’s the other thing I’m doing. All of this is with my former student, now Professor R. Burcu Cakirli in Istanbul.

Zierler:

Oh, I was going to say when you said “we,” I was wondering who the “we” was.

Casten:

Well, her and also a guy named Aaron Couture at Los Alamos for the r process. A lot of this is related to nuclear masses, so Klaus Blaum in Heidelberg, a guy named Denis Bonatsos in Athens who is an expert on group theory, Jan Jolie in Cologne who has similar interests as I do in symmetries, interacting boson model. . . Others. One guy I am not specifically working with but did some papers with earlier who does a lot of brilliant work on nuclear structure, and I love to talk to and learn from, is Piet Van Isacker, who is a symmetry-oriented theorist at GANIL in France. And, of course, I have had a huge number of discussions and joint work with Franco Iachello of Yale for more than 40 years. In fact, twice, we published back-to-back Phys Rev Letts where he announced a new theoretical breakthrough and we provided some experimental evidence for it.

Zierler:

How well are you able to continue your research from working remote, without being able to travel?

Casten:

It’s okay. It works. I was scheduled to go to Los Alamos for six weeks this summer. That’s just been canceled, but by chance we’re at a stage in a project there that can be done remotely. I was also scheduled to go to Berkeley for a month in October to work with Augusto Macchiavelli and Rod Clark, two more great guys with lots of ideas. That’s going to be a little harder to do remotely, but probably okay.

Zierler:

Well, it will be only more to look forward to next year.

Casten:

Yeah. And by the way, the main interest I have is experiments at FRIB with exotic nuclei.

Zierler:

Right.

Casten:

That’s going to be really exciting.

Zierler:

Right, right.

Casten:

They can wheel me in in a wheelchair to do the first experiment.

Zierler:

[Laughs]

Casten:

I should tell you about other things I do. What do I do besides being a nerd? I play about 14 hours of tennis a week, some golf, quite a bit of serious photography. Subatomic physics is easy. Golf is hard. I mean, you're trying to put a ball… You're trying to hit a ball a quarter of a mile and by hitting it four times, land it in something the size of the palm of your hand. But physics comes in, same physics that comes in in tennis and tornadoes and other things. Anyway. And travel—I’ve traveled tremendously. I’ve been to every continent, including Antarctica. Mount Everest. We do a lot of high mountain hiking/backpacking, up to about 16000-17000 feet. Anyway, so those are some of the other things.

Zierler:

Mount Everest. That’s pretty good for an asthmatic.

Casten:

Well, yeah. The asthma story is interesting. I’ve never let it stop me doing anything. When we hike in the mountains like in Colorado… Do you do any hiking in the mountains?

Zierler:

I do, yeah.

Casten:

So the general idea is you should hike at a nice, steady, continuous pace. I can't do that. I get out of breath quickly, and so I hike faster and stop and catch my breath while other people catch up. So it’s pulsed. That’s why I can play tennis but not soccer. Soccer is continuous motion.

Zierler:

Right.

Casten:

I still couldn't run flat-out around a tennis court, but you have gaps in time in a tennis game where the motion stops. Do you know what a pulse oximeter is?

Zierler:

I’ve heard of it.

Casten:

It’s a thing you put on your finger to tell—

Zierler:

Oh yeah, right. Sure. Right.

Casten:

So normal values, your values are 97. Mine are typically 93 or 94. Anybody who gets below about 88, the doctors in the emergency room begin to worry. When I play tennis, I’m at about 75.

Zierler:

Oooh.

Casten:

When I was in Tibet, I got down as low as 49. Most doctors will say the only people they’ve ever seen with readings like that are either dead or in comas or delirious. So I’ve learned to deal with my asthma, and my asthma, it’s not a lung problem. It’s a highway problem, in and out. So okay. And it’s gotten better over the years.

Zierler:

Well, that’s good!

Casten:

I’ll give you one example. So you recognize this rescue inhaler, right?

Zierler:

Sure, sure.

Casten:

I used to use an entire canister, 200 doses… I used to use this roughly ten times a day. The last time I used it, except very occasionally during tennis, was in October 2016.

Zierler:

Oh, wow. That’s great!

Casten:

Not once. Not once. In fact, the expiration date on this is September 2016.

Zierler:

How did you do it? What did you figure out?

Casten:

I don't know. I don't know. Oh, when I went to Everest—I don't know if you care about this stuff. When I went to Everest, my asthma doctor at Yale… First of all, he told me, “Don't do it.” Secondly, we arranged so that I would text him my pulse oximeter readings. When I got there and texted him the first one, which was I guess a value in the mid-60s, he texted back, “Oh my god. Good luck.” That’s an interesting bedside manner. In fact, our exchange of text messages became an article in the Yale Medicine Magazine about this sort of interaction between him and me.

Zierler:

So you're a physical specimen yourself.

Casten:

[Laughs] Yeah, I guess so.

Zierler:

Well, Rick, it’s been so fun talking with you today. I’m so glad we had this time to spend together.

Casten:

Okay. It actually lasted, what, three hours.

Zierler:

Almost three hours, so I’ll cut the recording here.