Stephen Seltzer

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ORAL HISTORIES
Image of Stephen Seltzer

Credit: Francine Seltzer

Interviewed by
David Zierler
Interview date
Location
Video conference
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Interview of Stephen Seltzer by David Zierler on March 9, 2021,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
www.aip.org/history-programs/niels-bohr-library/oral-histories/47145

For multiple citations, "AIP" is the preferred abbreviation for the location.

Interview with Stephen Seltzer, retired from the National Institute of Standards and Technology where he was Leader of the Dosimetry Group in the Radiation Physics Division. Seltzer discusses his current interests in photoelectric cross sections and he explains why NIST supports research in radiation physics. He recounts his childhood in the Washington DC area, he describes his education at Virginia Tech and his first job at the National Bureau of Standards. Seltzer describes the advances in ionizing radiation at NIST during his junior years and the formative mentorship provided by Martin Berger and his pioneering work in radiation science and Monte Carlo calculations. He explains why Monte Carlo codes provide a solution to the Boltzmann Transport Equation and why electron transport research provides value to space exploration and how NIST contributed to proton therapies for cancer. Seltzer discusses his administrative service as leader of the Radiation Interactions and Dosimetry Group, and he explains his motivations to serve as a mentor to younger colleagues at NIST. At the end of the interview he reflects on the budgetary environment at NIST over his tenure and why young physicists should consider NIST as an excellent place to pursue a career. 

Transcript

Zierler:

Okay, this is David Zierler, Oral Historian for the American Institute of Physics. It is March 9, 2021. I am so happy to be here with Stephen Michael Seltzer. Steve, it's great to see you. Thank you so much for joining me.

Seltzer:

My pleasure.

Zierler:

So, to start, would you please tell me your title and institutional affiliation?

Seltzer:

Well, I'm a retiree, at the National Institute of Standards and Technology. I retired in 2010, and before I retired, I was the leader of the Dosimetry Group in the Radiation Physics Division. So that was my title; and now, I'm just a retiree. I guess I'm considered a contractor at NIST. They give me a badge, vet me for security reasons, and provide office support.

Zierler:

As a guest researcher, are you free to pursue anything that's of interest to you? Or are there specific projects that you're contracted to work on?

Seltzer:

No, the former. I'm pretty free to do what I wish. At the very beginning, I did have a contract, but not with our Group and Division directly. Since then, it's part a favor to retirees when they want to come in. I do some research, consult with people, and talk to people. I'm the contact for a number of online databases that NIST maintains, since I was involved in their creation. I answer emails, I talk to staff. But it's been, now, eleven years. I have to admit that my direct participation is becoming more attenuated over time.

My wife had been after me to retire, and so I did. I retired on a Friday, and on Monday, I got up to go back to NIST as a retiree. She said, "Wait, you're retired." So, I promised her I would take Mondays off as proof that I'm retired. Thus, I used to go in four days a week. I still maintained that before we were sent home for the pandemic. But I have to admit, I go in later and leave earlier, take one of the grandkids to the orthodontist, etc. So, my duties are, really, quite light. But they're still very nice to me having me come in.

Zierler:

Given that you're free to do any kind of research that you want, what's been most interesting to you in retirement? What kind of research projects have you taken on?

Seltzer:

Well, there was a very highly technical issue when I left, and I had been involved in it over the years. It has to do the photoelectric cross section. So, I spent, I'd say, the last two or three years looking back at that. It became an international issue, actually. There is the BIPM, the International Bureau of Weights and Measures. It houses scientists who service the Treaty of the Meter, and they gather scientists from all over the world to talk about measurement issues. There was a report for the International Commission on Radiation Units and Measurements, for which I was the chairman of the report committee on Key Data, which was requested by the Dosimetry Group at the BIPM. And we brought up this issue regarding the photoelectric cross section, but we couldn't resolve it in the ICRU report. Very technical. Little point in describing it; it would be rather boring to most people.

However, the BIPM decided on their own that they would require something called renormalization of this cross section. In our ICRU report, we couldn't decide whether it was good or bad. We remained neutral in the report. And so, I spent the last two or three years just redeveloping our online database so that you could choose which photoelectric cross section you wanted: with or without renormalization. I haven't put it online; I'm just writing a report on it now. Because I'm not sure, if we put it online, if a user would have any notion of which one to choose. But that's what I've most recently done. Before that, I was tying up loose ends, serving on a few committees, and that sort of thing.

Zierler:

The question we're all dealing with right now, with you not being able to go into the office and have access to instrumentation and things like that, how have you been able to keep up your work remotely?

Seltzer:

They give me access to my NIST files. Long before the pandemic hit, all my working files on my NIST networked computer were backed up to a file system, a storage system, for security. We've all had failures; hard drives go bad. And so, everything is saved on a so-called Z drive. After the pandemic, they gave me an RSA token and a virtual hookup, so I can log in and access all my NIST files and my NIST email. Actually, for a while, I didn't. For a few months, I didn't do that. But then, I would start getting some emails from my colleagues at NIST about questions going on that I knew nothing about because I had not established access.

So, I got access. I can see my own files and was able to write a report on the work I was doing. I'm still hampered somewhat because I have a non-networked PC at NIST on which I do all my calculations. I'm a dinosaur, so this was an old DOS box. It had Windows as well; it has a dual boot. I might be one of the last remaining people using DOS. I guess it made Bill Gates rich. And I really can't do anything that requires access to this PC because I can't access it remotely. I was actually planning on going into NIST and bringing that computer home, so that I can do some more work and finish up things. For example, I get requests to provide data for some people, and I can't do it because all my calculations are done on this box, and I have no access.

Zierler:

Are you fully vaccinated yet? Does going in become less risky for you at some point?

Seltzer:

Actually, yes. Our two weeks after the second shot are up on Friday. It makes me feel very comfortable. Both my wife and I feel, really, quite comfortable. We're not crazy. We didn't burn our masks or any of this foolishness. But we're looking forward to maybe hugging our grandkids and going into stores or restaurants that we never have done during the pandemic. In fact, I think Friday, we're meeting a couple and going to eat inside. They're also vaccinated.

Zierler:

The CDC just said that's okay. Enjoy yourselves.

Seltzer:

I know, and it feels very odd after twelve months of being so cautious. I'm almost a little afraid to relax. But it is a better feeling. And, of course, everybody's worrying about the mutations and variants, but we'll see.

Zierler:

An overall question to our audience of researchers at the Niels Bohr Library who might not appreciate big questions about what governing agencies do with regard to physics. So, I wonder if you can explain, at a very broad level, why NIST is in the business of supporting ionizing radiation and radiation physics.

Seltzer:

I hope I can. I have to admit, NIST, which as you know used to be the National Bureau of Standards, was set up originally, to maintain the nation's measurement standards. What was that, 1901? There was a Congressional act to set up such a federal agency. I started working there in 1962. We used to call it simply The Bureau. I'm sure, for the purposes of this interview, you're not interested in anecdotes. But we always called it The Bureau. And at cocktail parties, people would ask, "Where do you work?" and I'd say, "The Bureau." And they thought I was an FBI agent. But at the old bureau on Van Ness Street, it was a bunch of rather old buildings, I remember some really good work was done. I was aware, once I got there, that standards work was important, but I was really never involved in it at the outset. I was in the Radiation Theory Section, and that's where we started developing Monte Carlo methods. But the ionizing radiation, the standards, which they'd started before I got to NBS, are for dosimetry, radioactivity, and even some neutron fluence standards, perhaps which came a bit later.

But radioactivity and ionizing dosimetry were important, as you remember. Madam Curie and radium, and then, of course, later, with Roentgen and x-rays, both of which were used to treat cancer. And people needed to have a reproducible way of measuring what we'll call dose. The original dose was redness. They would irradiate you, either with radium or x rays, until your skin got red, and decided they shouldn't irradiate anymore. But this is hardly reproducible. We, now, in our age, can borrow from other institutional experience. They'll do trials, perhaps in St. Petersburg or elsewhere, and their success might want to be duplicated elsewhere. The unit of absorbed dose for ionizing radiation is now called the gray. It used to be called the rad, but it got changed to the gray. And what's important for the international community, or even progress in science in general, is that, if in Russia or China, they treat somebody to so many gray, and have success, they might be able to borrow that protocol in Hopkins or Loma Linda, try it, and see that it works.

So, it's transportable. They know how to measure the absorbed dose, and they now trust that if someone else delivered fifty gray, that they can also give fifty gray. In radioactivity, the fundamental unit is the becquerel; it's the number of emissions per second. And there are others. X-ray dose as well, absorbed dose from x-rays. Air kerma, which is sort of obscure, is related to absorbed dose, but it's measured in air. So, it's sort of more of a measure of the output of an x-ray machine. And as I said, I'm not that familiar with neutrons, but I know neutron fluence had always been very important since the days of reactor physics, and particularly for public health, radiation protection. You need these, all of these quantities. So that's what the standards are for. The more mundane standards were length at NIST, and mass, of course, frequency, the atomic clocks, and many more. So NIST is the United States’ standards organization, just as the PTB is Germany's. Most of the major countries have a standards organization. And that's what they do. They maintain the standards. And we all meet regularly.

Well, when I used to do this, we would meet and compare, and everybody would try to get close to one another. In other words, if your standard was very, very different, you had to wonder why. And either you did something much better, in which case, other people wanted to copy it, or you were just an outlier, and you had to go back and look at your equipment to see what you were doing wrong. So, for all of these standards, whether it's light output in lumens or what have you, there's relatively tight agreement all throughout the world, which gives you even more confidence. I mean, if you go to buy a pound of sugar, you're pretty well-assured you're getting a pound of sugar no matter where it comes from.

Zierler:

Let's take it all the way back to the beginning. Let's start with your parents. Tell me a little bit about them and where they're from.

Seltzer:

My mother was born in Manhattan. Her mother and father emigrated from England. They were actually born in Poland. It's interesting you ask that. Over the years, both my wife and I were trying to find out stories about our immediate ancestors, but we were never very good at it. But now, there are all these people that do these wonderful family trees and genealogy. My father was born, as I recall, in Maine. My paternal grandparents were born in Eastern Europe, but I'm honestly not sure where. I assume Poland, but I really can't be sure. My father moved to Manhattan early in his life, possibly as a teenager. He was a schoolteacher, and my mother was mainly, thinking back, a secretary. She actually had her own secretarial business as I was growing up.

Zierler:

When did they get to this country on your mother's side?

Seltzer:

I'm not really sure. My mother died about five years ago, she was born I think in 1914. But I really don't know enough about my grandparents. I would like to have known.

Zierler:

Do you know a little bit more about your dad's side of the family?

Seltzer:

No, I know even less. In fact, I was contacted, interestingly enough, through NIST. Somebody saw my page or my name on the NIST webpages, and his name was also Stephen Seltzer. He contacted me, and he had been doing his whole family tree. And he had pictures that I'd never seen before of myself and my brother and was sure that I was a member of this family. He had this very elaborate family tree with all sorts of facts and dates, even knowing that my paternal grandparents lived in Maine. And I thought, "Wow." But he had them owning some soda factory. And I finally figured out that he was wrong, we're not related. It would've been very nice because I then I would have all sorts of relatives I'd never known about. But I know some of his facts were incorrect about my family.

My paternal grandfather was, variously, a baker and a barber. And I only remember snippets. I have a terrible memory, by the way. But I do remember snippets. He ended up being a baker because he was left-handed, and in those days, people didn't trust a left-handed barber. Although, he did cut my hair as a kid. My mother and father were divorced when I was four years old, so I would go to New York to see my father on occasion, and I saw my grandparents then, but not often. Whereas my maternal grandparents, most of my life growing up, we lived together. It was the only way we could all afford to have a house, by sharing a house.

Zierler:

And what neighborhood did you grow up in with your mom?

Seltzer:

Well, after the divorce, I'm told, we moved from the Bronx to somewhere in Northern Virginia. For a four-year-old, to me, it was some sort of place in the wilderness. I remember we had a mailbox on a post, and there were no sidewalks. But I honestly can't be sure because I don't trust many of the memories I have. It could be just stories that I’ve internalized. And my uncle, my mother's brother, had something to do with it. He had property, maybe rented her the house. I honestly can't remember. We didn't live there that long, then we moved to Northeast DC with my grandparents. They came from New York and moved down to DC, and we all lived in a little row house in DC. I grew up there. We left when I was in the fifth grade and moved to Maryland, Montgomery County, actually. And I've been here ever since. Well, I briefly lived in Prince George's County when we got our first home. It was not that far from the University of Maryland. We lived there maybe seven years, and then back to Montgomery County.

Zierler:

What schools did you go to?

Seltzer:

Emery Elementary School in DC. We moved in the fifth grade. I'm sure I knew it at one time because I had to fill out all these forms for a security clearance, but I don't remember the name of the elementary school in Bethesda. Then, I went to a brand-new elementary school that'd just opened in my neighborhood on Grubb Road right off the East-West Highway. We were the first graduating class. From there, I went to Leland Junior High in Bethesda, which no longer exists; I think they tore it down. From there, I went to BCC, Bethesda Chevy Chase High School.

Zierler:

When did you start to get interested in science?

Seltzer:

In high school, I liked science. I have to admit, watching my grandsons go through school, life is very different now. They get algebra, even some calculus, and pretty deep science courses. I took a semester of chemistry. My teacher was an elderly gentleman who wore a three-piece suit and vest and had gray hair. And he remembered being taught that atoms were considered little billiard balls, before atomic theory explained everything. But I liked inorganic chemistry. It made sense to me. Things clicked. I could understand valence, valence electrons. I liked most of the math we had. We didn't have calculus, but trigonometry and algebra. And then, I had one course, I think, in physics, one semester. And I thought this was really neat.

So, between chemistry and physics, I decided, "I want to do something in science." I liked them both, so I decided I would be a chemical engineer, thinking it was both chemistry and physics. It turns out it's really neither one, although it is pretty heavy on chemistry. When I got to organic chemistry in college at Virginia Tech, I realized, "I don't like this." And there were a couple guys in my dorm, they could've been juniors or seniors, in physics, and I talked to them, saw what they were doing, the kind of homework they did, and I said, "That's what I want to do," so I switched to physics.

Zierler:

I'm well-positioned to appreciate that organic chemistry has been the source of a physicist's career, many times over.

Seltzer:

Yes. I mean, everything prior to that made sense. You could derive things. Organic chemistry, you just have to know it. I'm sure at the atomic level, it makes sense. But I just couldn't figure it out. You just had to know it. It's like, if you want to be a physician, you have to know all the bones and the muscles in the body. It doesn't have to make sense; you just have to know it. And as I said, I'm not blessed with a wonderful memory. And so, those sorts of areas were clearly not for me.

Zierler:

Were there larger national programs like the space race or the moon landing that captured your imagination and might've encouraged you to think about a career in science when you were growing up?

Seltzer:

Honestly, I don't recall that. Most of what you're talking about happened after I graduated. I graduated with my bachelor's in 1962. Sputnik and all that were in the fifties. And I thought it was neat, but it didn't seem scientific. But it was neat. Rockets, to me, are an engineering feat. But then, the space race and all the rest of it started when I started to appreciate things. And, of course, for moon landings and most of the Apollo program, I was glued to the television. I thought they were some of the most exciting things I had ever seen. And I sort of recall the second moon landing happened to be during a football game. Could it have been a Super Bowl? I honestly can't remember. But they switched coverage from the game to cover this moon landing, and people were all upset. They wanted to see their football game. And I couldn't fathom that kind of thing. These were men walking on the moon. I realized it wasn't the first time, it was already the second or whatever, but I just couldn't fathom that. But my die was cast. I was already a physicist by the time this happened. In fact, I interviewed at Goddard Space Flight Center when I was graduating from Virginia Tech. But I didn't like the job.

Zierler:

Between your grades, your family's financial considerations, geographic considerations, what kinds of colleges did you apply to when you were a junior or senior in high school?

Seltzer:

Again, times were different. I never considered a scholarship. I honestly don't recall anybody talking about scholarships and financial aid. I graduated from a Maryland high school, and, at that time, I was guaranteed a place at University of Maryland, College Park. That now is no longer the case, as you know. It's highly competitive, even for in-state students. My older brother went to University of Maryland, and I didn't want to go there. I wanted to go somewhere away from home. My brother had a friend who went to Virginia Polytechnic Institute, Virginia Tech, and I remember he came to our house one evening; they had a corps of cadets. At the time, he was a cadet, and he came in his uniform. And he mentioned a little bit about the school. So, I looked into it.

And it turns out VPI was relatively unknown at the time; nobody I knew had ever heard of Virginia Tech. Now, they all follow Virginia Tech in the sports pages. But then, my friends had heard little of it. I looked into it, and I found out I could go there, even as an out-of-state student, and afford it. We didn't have much money. However, I was never hungry, and we lived in the Maryland suburbs. So, we did all right. The other thing that attracted me to Virginia Tech was that they had a co-op program. They were on a quarter system. So, after the first year, you would work a quarter, go to school a quarter, and bounce back and forth. You had to write a report on the quarter’s co-op experience. They would help you get placed in a position that was related to your course of study.

And so, I did that and made enough money co-oping to pay for college. So, I never really had to borrow money. Maybe I'd saved $1,000 by the time I went off to school, and that was enough. It was affordable then. It's obscene now. I feel really bad. Obviously, you're a graduate. I don't know if you had student loans, but that was then unheard of for an undergraduate. Graduate school, perhaps. Most people who went to graduate school were a teaching assistant or got some financial aid. But you didn't come out of school owing tens or even hundreds of thousands of dollars. That, to me, is just obscene. So, it was affordable, and it was a nice experience.

Zierler:

When did you declare the major in physics, and was there a particular professor or course that made you want to focus on this area?

Seltzer:

I think I declared in or just after my sophomore year. I remember some interesting professors. There was one fellow trying to teach me calculus in the math department. I thought he was really quite smart. I thought most of the professors were rather good, but I don't remember being particularly inspired by them to be a physicist. I don't know what to say. As I mentioned earlier, there were a couple guys in the dorm that were physics majors, and I thought what they were doing sounded cool (laughter). I mean, come on, I was eighteen, nineteen years old. You want to be cool.

Zierler:

To the extent that you recognized that there was a divide in physics between the world of theory and the world of experimentation, where were your interests and talents? What did you want to focus on once you declared the major?

Seltzer:

I never had particular talent with equipment. I had to work with it. I will admit to you, and to everyone, I guess, that I never understood electronics particularly well. I had to take courses in it. But I didn't feel it. For example, electrical engineers, they feel this stuff. For example, I never really understood inductance. Fourier transforms are an important component in physics and mathematics. But for electrical engineers, Fourier components are palpable. I never got it that well. I actually was a lab assistant; I think my senior year as an undergraduate. In addition, they had me fixing Geiger counters and perhaps a few other instruments. I could do rudimentary things, but I was never particularly talented with equipment. And that was borne out later, when I had a little bit of a reputation that people didn't want me to get too close to any of their equipment in the laboratory because I might break it.

One of the first things I did, I remember going to a night-vision lab in Virginia, and they were showing me, I think, second-generation night-vision scopes. One of the components they handed me the aluminized screen, and I stuck my thumb and rubbed off the aluminum coating. And the guy said, "Oh, oh, it's okay, don't worry about it." Well, of course, he had more, but I felt like an idiot. And I remember going into our x-ray lab at NIST, and the head of the lab would tell me not to touch anything. Well, they didn't want me to get electrocuted either. So, "Be very careful." So yeah, I'm not particularly adept with equipment.

Zierler:

Did you ever consider going straight into graduate school, or did you want a job right out of college?

Seltzer:

I did get a job right out of college. I looked into, actually, going to Johns Hopkins for physics. I think I could have gone there, but I couldn't afford it. As I said, right out of undergraduate school, I went to NBS, and they had courses taught by NBS staff who were adjunct professors at the University of Maryland. So, I took a number of graduate courses at NBS after hours. And even when we moved to Gaithersburg, I continued to do a bit of that. As a result, I had a fair number of course hours. And I took some of the more on-campus courses thinking, "I will go for a PhD at University of Maryland in the Physics Department," and collected a bunch of qualifying exams to study. I looked at them, and I was scared to death. My wife said, "Just take the exam." And I said, "I'm not ready. I'm not ready." By the way, we also had two little girls at the time. So, I was studying at night, working during the day, trying to master these exams. For example, you have a dielectric top spinning on a metal wire, and they ask you some electricity and magnetic question, I couldn't possibly come up with those answers, so I wrote a thesis, got a master's degree at the University of Maryland, and called it quits.

Zierler:

Did NIST support this? Did they want you to get a graduate degree?

Seltzer:

Yes, they were very good about that. They paid for all my credit hours, including the thesis hours, which seems to be just a fee you have to pay to the university. You don't get anything out of it other than the degree because nobody does anything for it.

Zierler:

Did you ever consider going on for the PhD?

Seltzer:

Not after that, no. I sort of regret it. I remember meeting people, colleagues, who got PhDs. And I was thinking, "I don't think they're any smarter than I am. But they passed the qualifying exam." I never even took it. My wife said it was a big mistake. I should've at least tried to take it. But anyway, it's too late now.

Zierler:

To go back to 1962, did you sense the excitement of the Kennedy Administration and his interest in supporting and expanding science at the federal level? Did that sort of filter down to your level?

Seltzer:

I think a bit. We were, early on, involved in doing some Monte Carlo calculations in support of the Apollo program. The very early parts of the Apollo. Even before Apollo flights. They were worried about radiation effects for astronauts in the inner and outer belts. I was aware of it, but I was also very young. So, I'm not sure I could honestly say that I was infected by the excitement. But I have to admit, I was always a big fan of the space program. I can't remember when I got excited, but I was certainly excited about that. And both my wife and I remember coming home that evening when Kennedy was assassinated. That's the biggest memory of the Kennedy years. But the excitement was there for the space program. And yeah, I think I was bit by it.

Zierler:

What were some of the advances in ionizing radiation that NIST was a part of during your early career?

Seltzer:

Well, Lauriston Taylor had devised a free air chamber, which measured what we now call air kerma, which at that time was called exposure. That was some of the early days of the international efforts. And it demonstrated very good reproducibility and accuracy and helped focus the international instrumentation on x rays. He left NBS to found the NCRP. NBS had a betatron. I don't remember much, but they did do that. That betatron that left the old Bureau went to the new Bureau in Gaithersburg and became a light source. And now, I think they built another one that has higher output. So yes, that became a national resource, actually. And it started back when I was there. But I don't recall it being noteworthy. But again, I was young, I was scared. I was around people who were very accomplished. And I was there with a bachelor's degree, and I didn't know anything.

And so, I pretty much concentrated on just trying to do my job, whatever they told me to do. And so, I was only vaguely aware of things that were going on elsewhere at NBS. We were housed in the old High Voltage building, gone now, which had an electrostatic accelerator in this gigantic room with this big ball. They would charge up this metal sphere, and then lightning would zip across the room. It was like a scene out of Frankenstein, to be honest with you. It was a lot of fun to watch. But the Radiation Theory Section was housed up on top of the building, literally in the penthouse, which was on the roof. Before I got there, they had built, essentially, a little frame house on top that had half a dozen offices and a little main room up there. It was not small. And it had a little door out to the actual roof, so you could go out on the roof on a nice day and enjoy the fresh air. It was called the Penthouse. So, I was sort of separated from the rest of the people in the Division. I got to know everyone, but I wasn't there for the day-to-day things. So, I was in a little bit of an ivory tower. And as I said, I was very focused on just trying to do my job.

Zierler:

Were you a witness at all to some of the broader considerations about establishing a NIST presence in Boulder?

Seltzer:

No, I was not. I have to admit, I got more familiar with the Boulder operations much later, maybe twenty or twenty-five years later. I was assigned to the laboratory office as a scientific advisor. They have a number of positions at NIST, in which they take people, we'll call them bench scientists, and move them into more supervisory roles. So, I worked with the lab director in a position that was sort of training for possible future supervisory roles. There were administrative meetings, and some of the meetings were in Boulder. And I became a bit more familiar with Boulder operations. They would review the laboratory program, so I became much more familiar with those activities in our laboratory. Of course, I knew there was a Boulder operation long before this. I knew of WWV, the radio frequency broadcast, all traced to Boulder. I think that was one of their initial successes. And then, of course, the atomic clocks, and all that were done at Boulder. So, it was very, very impressive. But no, I was not as familiar with the Boulder programs as I was with those in Gaithersburg.

Zierler:

I'm sure it didn't happen overnight, but at some point, you must've stopped feeling like a young, inexperienced college graduate surrounded by these very accomplished people, and you felt like you were gaining some seniority, you were gaining some knowledge in the field, and some confidence in doing your own original research. When did that happen for you? When did the confident years start?

Seltzer:

Well, my wife thinks it's some sort of false modesty, but it isn't. I never felt as confident, I think, as some other people do. Looking back, I've had, I think, some solid successes. I was a supervisor, and the program went well. But I never felt that confident. I never had that sense.

Zierler:

The awards you've gotten, all of the requests you've gotten to serve on committees didn't do it for you?

Seltzer:

Of course, they helped, but I couldn’t fully understand why I got them. I always thought I basked in reflected glory. I had worked with some very, very good people, but I think a number of good scientists that I've known actually thought I was pretty good. I always thought it was because of my association with Martin Berger, Ugo Fano, or some of these others that came before me. I realize I'm not a genius. I think I possess a certain cleverness that has helped me be successful, and it is true, I did get put on a number of what I consider, at least in my field, prestigious committees. And I very much enjoyed them. But I always assumed that all the other people in the room were much more confident than I was. I'll put it that way.

Zierler:

Maybe they felt the same way, you never know.

Seltzer:

Well, I will admit, I just assumed that they were confident.

Zierler:

When did you first meet Martin Berger?

Seltzer:

Just before I joined NIST. I had never met him before. Toward the end of my senior year at Virginia Tech, they had job fairs, where recruiters would come to campus. They set up booths and spoke of opportunities they represented. And I went to them. I was married my last year in undergraduate school, so my wife and I lived in Blacksburg, Virginia, in a little apartment. After the job fair, I came home, having talked to a number of recruiters and mentioned, "Gee, I could work in the aerospace industry in California." I thought that sounded neat and would provide a warm, sunny environment. But my wife said, "No, no, no, no, no, no. My family's in Washington. We're going to go back to Washington." I said, "Okay," and I sent in the standard form for jobs in the federal government. One was for NASA, but I don't remember if I knew NBS was recruiting. However, I got a letter indicating possible work at NBS. On a visit home in the DC area, I went to NBS, and I stopped by to see Radiation Theory.

And so, I met Martin Berger. I also visited Fire Research in this musty old building that smelled of smoke and soot. There was a physicist there, and he literally had sleeve garters, gray hair and glasses, and showed me these little concrete bunkers where they set fires. And I was thinking, "I don't want do that." I went up to the Penthouse, and I briefly met Martin Berger and some of the others. Then, I went back to Blacksburg, and I got a call from Martin Berger asking if I would like to work there. And I said yes. I got off the phone, and my wife wanted to know who that was. She said, "You were so phlegmatic. You have to call him back and tell him you really want to work there." So, I did call him back and apologized. But that's when I first met Berger. It was literally within weeks of starting there.

Zierler:

I wonder if there was a certain amount of naivete for you, not knowing who Martin Berger was.

Seltzer:

I had no idea. I had no idea who any of these people were.

Zierler:

Right. Right. And no idea how significant the work they were doing was.

Seltzer:

No, but I thought it was neat. I really thought it was neat.

Zierler:

What do you think Berger saw in you to get this personalized phone call invitation?

Seltzer:

I don't know. I hate to keep emphasizing my inferiority complex. It's not really a complex, but I really don't know. I guess he looked at my record, thought I was a bright guy, and just gave me a chance. I don't know how many other applications he saw. I never asked him, to be honest with you.

Zierler:

Once you started working with him, what did you realize he was after, the big research questions he was working on?

Seltzer:

Well, I thought he was brilliant. You have to remember, Ugo Fano was, at that time, our Section chief. I learned later, not immediately, he was brought to NBS, I guess, by Astin. And he wanted to start a program in Radiation Science, and he wanted to build it from the bottom up. He was a brilliant theorist, by the way, Ugo Fano. And I guess he must've recruited Martin Berger and a number of others. Lew Spencer, Lenny Maximon, a number of other physicists. He wanted to build Radiation Theory from the ground up, including knowledge of all the cross sections for interactions of radiation with matter, and I thought that was an important core principle that he had. He, and Martin Berger, Lew Spencer worked, essentially, on methods of solving the transport equation. But they didn't skimp on the development of cross-section databases.

And so, when I got there, John Hubbell had already been working for some years on the development of large databases of photon x-ray interaction cross sections. Martin Berger had worked a bit on it. And so, when I got there, we started looking at, Martin and I, the transport of mainly moderate-energy electrons and photons in matter. Looking at some non-Monte Carlo methods as well, but we needed a lot of data. But Fano, and Berger, and Spencer had other work where they were looking at moment’s methods, all sorts of other types of calculations for the transport of radiation through matter. I was just a small part of it. I assume Berger was given a slot so he could hire a new person. But from the outset, it seemed clear I was working with Martin. I had interactions with the other scientists, but Martin and I were working together.

Zierler:

And, of course, the dynamic was, he was your mentor. You weren't obviously working with him as a peer at that point.

Seltzer:

Oh, absolutely. I knew next to nothing. I got to work, and they handed me a slim brochure, maybe a dozen pages. It had a colorful cover, heavy paper cover, and it said Fortran. Fortran was brand new programming language at that time, and I had to learn Fortran. Before that, Martin Berger was involved in coding with machine language, and I think he had done some Monte Carlo work. But they had to do it using machine language. I had the luxury of doing it in Fortran, which is a higher-level language, and it was much better.

So, I didn't know anything. I didn't know how to use a computer. I also did a lot of hand calculations at my desk on an old Marchant, those clickety-clackety calculators. It was electrified so at least I didn't have to crank the handle. And you actually developed sort of finger algorithms. You could do square roots and such and watch how it hit the keys. I would write computer programs, on IBM cards using a card-punch machine, take them over to the Quonset hut where the computer was, submit them, and maybe get the results the next day. But I had to learn all of that. And that was my first task. They handed me this Fortran booklet and said, "Learn it." And so, in a couple weeks, I was writing some programs and trying it out.

Zierler:

Had you ever heard of Monte Carlo calculations or what their value might be before this work?

Seltzer:

No.

Zierler:

And was Martin the one who taught you about Monte Carlo calculations?

Seltzer:

Well, he taught almost everybody. He wrote a paper, and it was already in review by the time I got there. I think it was in Methods of Computational Physics. It was 1963 that it came out, and I had been there less than a year. And that paper has, by other physicists, been called the bible for electron Monte Carlo. It was a fairly long paper. He codified all the approaches to do Monte Carlo calculations particularly for electrons, and including the photon sampling, and presented a lot of examples. Obviously, the Monte Carlo method goes back to, what, the Manhattan Project, I think. So, it preceded Martin's work maybe fifteen or twenty years.

I knew he knew a lot, but I came to realize, quickly, that he was an expert, the world's expert on electron Monte Carlo. There were a few other codes around at the time, but they came from more of the very high-energy regimes, shower theory. It was a Monte Carlo approach to detail high-energy electron-photon showers. It was extended it down, over the decades, to lower energies until it could handle the moderate-energy Monte Carlo that we're familiar with now for cancer research, materials effects, etc. But yeah, I came to learn he knew a lot. And that was the first time I learned anything about the Monte Carlo method.

Zierler:

When did you first appreciate, once you understand what Monte Carlo calculations were, that they would be useful for electron, photon transport, and their applications, and things like medical physics and space radiation?

Seltzer:

I didn't start writing Monte Carlo codes right away. It could've been a year or two, when I was trying to do some other sort of numerical work, non-Monte Carlo, calculating some distributions. And, actually, Martin had an idea and gave it to me to apply it to some transport work. It was numerical. It wasn't highly theoretical. It had a theoretical basis, but it was just number crunching. And I never got it to work. I think I might've worked on it for six months, maybe nine months. I never could get anything out of it. And he just shrugged and said, "All right, don't worry about it," and we went on to other things. And started writing Monte Carlo codes. And incorporating refinements to cross sections and sampling schemes. But in writing a Monte Carlo code, I think I appreciated almost immediately that this could be used for almost anything that had to do with electrons and photons. Because the theoretical basis for radiation transport can be highly complex.

It's essentially a solution to the Boltzmann Transport Equation. But for most Monte Carlo-ists, or some of the colleagues I'd known to work with other codes, you really don't start there. There is a lot of neutron work and other approaches for which people start with the transport equation. For example, with moments methods, they develop numbers of schemes to solve the transport equation. But with Monte Carlo, essentially, you designate your initial electron or photon history, saddle it up, jump on that saddle, and you ride along as this particle bounces around through a material. And it's immediately clear that you can solve almost any problem. Problems get complicated. You have to worry about crossing a boundary, you have to worry about scoring different effects, you have to worry about all the interactions it can take. But you realize you can address lots and lots of different problems. I can't say that I immediately recognized the vast array of specific problems that one could, or even I would, eventually address, but you realize the power of it.

Zierler:

Maybe a way to get at the value of Monte Carlo calculations is, what problems existed in these areas of transport, of medical physics that Monte Carlo elucidated? What can we now understand that was not understandable or as easily understandable prior to the development of these calculations?

Seltzer:

Quite a bit. You have to understand that, particularly in radiation applications, an awful lot was done analytically, or semi-analytically. And most of such calculations were done under various assumptions. You could often get some reasonable results, but they wouldn't be strictly applicable to real situations because real situations are much more complex. You have interfaces, you have boundaries, you have all sorts of things that are very, very difficult to take into account in most of the analytical theories. At the time we were developing this, I'm not sure that I had much in mind, at least in the early sixties; that came in the later sixties and early seventies, for the applications to medical physics. I think one of our first applications was for the Apollo program, where we were calculating bremsstrahlung production by inner-belt electrons in the aluminum skin of the spacecraft that could be a hazard to the astronauts.

Zierler:

What is bremsstrahlung?

Seltzer:

It's a German word for breaking radiation. When an electron is in the field of an atom, it gets sort of decelerated, its path gets bent. And when it does, it emits photons. These are called bremsstrahlung, breaking radiation. There are separate cross sections for bremsstrahlung production in the field of the nucleus, the screened nuclear field, and another bremsstrahlung component in the field of the orbital electrons. That's what makes electron transport so complicated. Electrons have tremendous numbers of collisions. They're charged particles and are continually encountering atoms, which are made up of charged particles, for example the charged nucleus and the charged orbital electrons. The mean free path, the average path between collisions is tiny because you're seeing you're seeing electrons, you're seeing nuclei, all the time. Photons are uncharged, so they have comparatively very long mean free paths. You can go long distances with only a few collisions. But electrons are very complex because they lose energy and change direction over tiny dimensions.

And remember, back in the sixties, we, of course, used mainframe computers. They weren't all that fast. With x rays or photons, in Monte Carlo, you can follow a photon from collision to collision. You could do it back in the sixties. It wasn't that difficult. Depending on the amount of computer time you were given, you might not be able to solve highly complex problems with good statistics because computers were relatively slow and small (you didn't have a lot of memory). But for electrons, you couldn't even think about sampling individual interactions. So, one used other tricks. And when I talk about Martin Berger writing the bible, he elucidated all the tricks that one needs to use, he classified them, and it was, really, quite brilliant.

Zierler:

The idea that the work you were doing was relevant for the Apollo mission…

Seltzer:

Yes, and any transport problem. I didn't necessarily have a goal of saying, "Gee, I'm going to show the community how to do calculations to better use cancer therapy." I don't think that was in anyone's mind. Well, at least it wasn't in my mind at the time.

Zierler:

So that's the question, Steve. What's the point of contact or institutional collaboration that gets this research on the radar of NASA and the scientists working on the Apollo mission? Is it NIST making NASA aware of this research? Is NASA putting a general awareness out there that they needed answers in this one area? What's that point of connection where you're actually contributing to the Apollo mission?

Seltzer:

Well, I think that some of our work was published. There were meetings. I know Berger was giving talks at scientific meetings, professional meetings. And we had visitors. I remember a number of people coming up to the Penthouse, and we would talk about the capabilities of some of the early codes that we had and what the applications might be. I remember one gentleman, I think he was one of these so-called Beltway Bandits working for a consulting firm, and he wanted to borrow our code. I think we gave it to him, but Berger was very annoyed because he was just going to go and use it for the work he was selling, and he didn't like that. But I think we were contacted by NASA. I think it was NASA headquarters who had learned about some of the work that we were doing and suggested that we look at the bremsstrahlung production for the Apollo program. Very much later, I remember the National Cancer Institute coming to NIST and discussing with us some work. I also remember, later, doing work on calculating the absorbed-dose distribution in water. Tanks of water are always used in cancer therapy for measuring the beams from accelerators, and cobalt-60 units, and to measure the absorbed-dose distributions. Water is a good tissue substitute. And then, they translate those measurements into therapy planning. And I remember calculating absorbed-dose distributions from electron beams in water, and then plotting isodose curves, big plots back in the old days. We had someone who had come in from NIH and was consulting some of the experimentalists who were involved in the American Association of Physicists in Medicine, and I remember showing them the plots: "We can calculate this." And they go, "Nah, nobody's going to believe a calculated result. They'll all want to measure it." I always remember that.

It was some years later, but they started to believe in the calculations. And now, the calculations are almost preferable to measurements because they're cleaner, they're precise, and they can mimic real interfaces and unusual effects. But it took decades to be vetted and accepted. So that came much later, I have to admit. Radiation protection I think might've come a bit earlier. They were worried about health effects. Not as much precision. There were some national security applications as well through the Office of Naval Research that were brought to our attention. But somehow, I remember the space applications became better known to us after we moved to Gaithersburg. Our mainframe computers were okay. I wouldn't say state-of-the-art, but close to it. But IBM was installing an IBM 360-91 at Goddard Space Flight Center, and that was the supercomputer of its time. The footprint was probably at least as big as a basketball court. Spinning disks, tape drives, and what have you. So, we talked to the people out there, and I thought, "This will be great for Monte Carlo. It's supposed to be really fast."

They allowed me to use an office at Goddard Space Flight Center, I brought my decks of IBM cards, and I kept working on the Monte Carlo codes out there and used it to do calculations. As a result, I learned about other applications. I got to know a few of the people there. For example, they were interested in response functions for detectors used in space exploration, auroral physics, obviously, some shielding studies, and those sorts of things. But part of it is that you literally just get to know people. And with going to professional meetings and talking about your results, word spreads, somebody calls to say, "Well, gee, how about this? Can we look at the interface between the silicon and the gold contact in a transistor?" "Yes, we can look at that." So, things just branch out. You start looking at other applications. Word of mouth, contacts, meetings, what have you.

Zierler:

You gave a rather technical answer, but I wonder if you can explain specifically how your research actually contributed to the success of the Apollo mission.

Seltzer:

I'm not sure it did. We were very proud that they used it. I think they satisfied themselves that they wouldn't kill any astronauts or even – well, I shouldn't be smug about it. I wanted to say, "Or give them cancer." You don't know if you cause cancer. Cancer takes twenty years. So obviously, you could never be accused of that. But they wanted to know beforehand whether this was going to be a problem. We could do the calculations. I think there were some numbers that might've bordered on the edge of what they considered safe. But I got the sense that they were committed to the mission. I don't know that our results would be a go or no-go kind of thing. I think if there were any questions, I wasn't privy to the things that the NASA people might've discussed at headquarters, I assume that the numbers looked reasonable, and there shouldn't be any big problem. And, of course, things were looser then. Maybe if there were a few cases of relatively high dose, they weren't that concerned with it. But I'm sure that we in no part led to the success of the Apollo program.

Zierler:

As you called it, the IBM 360 was the supercomputer of its time. What did it allow you to do that previous generations of computers or obviously, a pen and computer, working out calculations manually, that wasn't possible before?

Seltzer:

I'm not sure whether I would say it wasn't possible. It wasn't practical. I remember doing calculations, in which I would do 10,000 or 20,000 histories. A history is an incident electron or photon hitting a target, and you'd follow it through with all the secondaries, the secondary photons and secondary electrons; you'd follow all of those through until the end, either they escaped, or they dropped in energy so that you didn't care anymore. So that's what we would call a history. I would do 10,000 or 20,000 histories, and even on an IBM 360, I could only do those at night when they weren't busy like during the day.

And that was a lot of histories for the time. Prior to that, you'd do 1,000, maybe 2,000 histories. If you had enough computer time, you could keep going, in principle. But few had that kind of computer time. But 20,000 histories were then a bunch. Now, you might do millions of histories. In fact, on a PC at work, I can sometimes do 100,000 histories: set up a run and go to the break room and get a cup of coffee and come back for the results. That's how much our computing power has advanced. So now, you can do hundreds of millions of histories, not hundreds of thousands. And some problems require it. They're complex problems, and they do require it. But I grew up at a time where you just didn't consider those complex problems, you did the easier ones, the ones that you could actually accomplish.

Zierler:

Kind of a broad question, in what ways were some of the advances, particularly in the early part of your career, the 1960s and seventies, when there were so many fundamental advances being made in elementary particle physics at places like Harvard and Princeton, and national labs like SLAC and Brookhaven, relevant for your work?

Seltzer:

Well, we kept an eye on things. Most of the new particles that were discovered, and new applications didn't necessarily impact our work directly. We actually had some collaborations with Oak Ridge. They were looking at pion beams for cancer therapy. So, we would do some calculations because pions would produce other things. We would do that part of the problem. I don't know if you've looked, but obviously later, protons, alpha particles, and light ions were proposed for cancer therapy, particularly as made possible by engineering advances. And so, of course, we looked at those. In fact, even working in proton Monte Carlo and alpha-particle Monte Carlo. But again, perhaps more importantly, we were also concerned with the cross sections that one needs to follow the heavier charged particles. So, we kept an eye out, but the energy region in which we were working didn't really involve many of the new exotic particles as they came online. I guess in principle, I never ran our codes to particularly high energies, but they'd go up to ten or maybe even one hundred GeV, in which meson physics can become important. I went up into the GeV region, but I made it clear that I ignored any meson physics.

And I also ignored any neutron spallation, and photonuclear physics, and things like that. Often, you just did your work with the tools you had. You didn't necessarily go to expand the tools to put in every new particle. Other people did. For example, MCNP, I don't know if you're aware of that Oak Ridge code–that now includes every particle. GEANT is another all-particle code. And they'd try to include everything known to varying degrees of exactness and precision that depended on what is known. So no, I wouldn't say it was necessarily the new elementary particles, but more the new developments in using some of the other charged particles in, say, medical physics or materials effects, etc.

Zierler:

You mentioned briefly the National Cancer Institute. When did you start to realize that your research was relevant broadly in medical physics and specifically in potential cancer treatments?

Seltzer:

Oh, I would say maybe the seventies and eighties. We had what I would call friendly competitors. There was a high-energy code called electron gamma shower, EGS, out of Stanford, and I think it was originally written by a German fellow. And they started adding more and more physics to it to support some of their work in radiation. Later, people at NRC Canada got ahold of it, and they improved it even more. This group were more heavily involved in physics in medicine and cancer therapy. One fellow, Dave Rogers, in particular was pushing the applications using that as a tool. We never pushed using our codes for any particular purpose. And as I said, I calculated dose distributions, but people were remarkably unimpressed. Even when I showed comparison with experiment (I'd put experimental results the plots), and they were really quite good. And they would just shrug. But that was a bit earlier.

By a decade later, everybody was using Monte Carlo to support therapy-planning systems, in elucidating effects, understanding interfaces, and what have you. So, we didn't focus on medical physics applications. I don't want to imply that other people did market, but they were just more involved. We just sort of skipped around applications. There was a visit from someone at NCI who came to NIST and talked about a number of possible projects, and one of the projects she mentioned was using protons for therapy. This was in the early days of proton therapy. Of course, you might know that we now have a lot of photon-therapy centers, Loma Linda being the first one in the U.S, but now numbers of them all over the world. And so, she was aware of our work, and Martin Berger said, "Yes, we'll do it." I think we got a grand total of $20,000, if I'm not mistaken. And this was maybe back in the eighties. This wasn't 1900; it wasn't a big pot of money. But she said, "Well, I'm particularly interested in all the secondary particles."

Because protons collide with nuclei, and they produce all sorts of secondaries, fragments of the nuclei. Those are heavy, they don't travel far. But because they're heavy, they interact with living cells much more importantly than protons do. They can be a problem. And she said, "Well, I want to know all about the secondary particles, as well." And Martin says, "Well, Steve Seltzer will do that." He told me about this after the meeting, and I said, "I'm doing what?" And so, he said he was going to write the proton Monte Carlo code, and I was going to look at all the secondary emissions, the heavy charged particles. I had to go all over to every national lab and center to find experts in spallation, and fragmentation of nuclei by protons; and I collected all the codes I could find. And I actually wrote a little report, but I didn't faith in much of it. I only made it a NIST report; I didn't publish it in an academic journal. But it was interesting. Other people did find it and improved upon it. It was really a lot of work, but I was a little annoyed I had to do all that work for a little bit of money. But it really wasn't my area. I was never really impressed with the product, but other people found it actually helpful.

Zierler:

I'm familiar with some of the marketing around proton therapy for cancer. How well has the technology developed? Do you see this as a potent tool in the overall fight against cancer?

Seltzer:

Yes. There was sort of a competition, early on at least. I think proton therapy is here to stay. It's expensive. The early modern radiation therapy was with cobalt-60 beams, if you remember your history. Well, before that, it was radium. But then, they had these cobalt-60 beams, and they could shape them. You had a big cobalt-60 source, and one could open little ports, and put absorbers around it and shape the beam. And so, you could make it conform to the shape of a tumor or organ, and you could irradiate from different angles. Photons tend to keep going. They do produce charged particles in their interaction, usually secondary electrons, photoelectrons, and Compton electrons, and they can give you the dose that's absorbed in the target. But the beams irradiate healthy tissue to get to the tumor site, and then keep going after the tumor site. Of course, they scatter, they go down in energy, but irradiate tissues other than the tumor. Then, they started using electron linear accelerators, which were very expensive at the beginning, but now are more affordable. They're incredibly good. They can irradiate tumors directly with electrons, but those electrons have a short range, so they're mainly used for surface tumors, skin treatments, things close to the surface because electrons can't penetrate very deeply. But they put in bremsstrahlung converters, so the electron beam hits typically a tungsten plate, a high-Z plate because they can get more bremsstrahlung from high-Z atoms, and again, as in cobalt units, they can shape these beams.

And so, now they can have high-energy photons. A cobalt-60 beam is mainly comprised of 1.25 MeV photons. A bremsstrahlung spectrum can go up to the kinetic energy of the electron, so it can go up to ten or twenty MeV, but it peaks at lower energy. So, it's almost equivalent in energy to cobalt. But it can be a much more intense beam. And it is easier to move the beams things around. They can put you on a table, and can zap you from different directions, and tailor the absorbed dose to conform to the target volume. But you still tend to get dosed elsewhere. Sorry to be so longwinded. Proton beams had been proposed for years. What's nice is that a high-energy proton actually can extend reasonably deep in the body, as it loses energy along the way. As it gets to very low energy, the rate of energy loss increases, reaches a peak, and then falls off. It just stops; no energy anymore. This feature was touted because one can irradiate a tumor with close to zero absorbed dose to tissue after the bean stops. So, they don't irradiate appreciably any a healthy tissue beyond the tumor. Well, the electron-linac proponents argued that because the they come in from so many different angles, the although it's true that the photons continue to irradiate tissue behind the tumor, it's relatively little. For example, by using ten beams, you get only one-tenth of the irradiation in any direction behind the tumor. They argued that their approach was cheaper and just as good. The proton people went ahead. It is much more expensive. It's a bigger engineering feat because a proton accelerator is large. They have beam lines with which they can transport the beam with magnets. They can guide the beams around different directions with gantries. And they've improved this method. But it is a much larger investment. And they also would go in from different angles and sides to try to paint the tumor with equal doses. And they do get that extra benefit of the sharp distal edge to the absorbed-energy distribution.

The original applications were for tumors near the spinal cord where it's very critical that you spare the spinal cord. They also use it a fair amount for prostate. They use linac cancer therapy for prostates as well. But there have been one or two applications for which protons are particularly well-suited. It works well in a number of applications, so it's here to stay. Then, the next big development was using light ions because, if you like protons, you'll love carbon ions. They're even heavier particles; they have a very high relative biological effectiveness, so they can kill cancer very, very well. And again, they stop at the end of their range. However, the physics is a bit more complicated because they produce a lot more secondaries.

And so, you have to worry about neutrons, as you do even with protons. Both produce a neutron background in the body. Ion therapy is gaining traction. I don't know how many light ion accelerators there are now, six or ten in the world, where they're doing cancer therapy. But it is a much more expensive therapy, and again, where it truly excels are in a few applications. For example, radiation-resistant tumors. But I'm not a medical expert. All this is pretty much secondhand.

Zierler:

Have you ever had opportunity with all of these advances to work with collaborators at places like NIH or FDA in approving these technologies?

Seltzer:

No. I won't say that I have. I've been consulted on occasion, asked a question by some of the people who are looking at approval applications for medical instrumentation. I've known people who do that, and they occasionally asked if I wanted to do it, and I said, "No, no, I don't think I want to do it." But I've answered a question or two. We actually went through the process, but more from the other direction; when we developed the Lixiscope, we needed to get FDA approval, so we had to put in our own application. But that was not reviewing it, that was writing it.

Zierler:

I wonder if you can unpack a technical phrase that's so fundamental to your career, and that is radiation transport through extended media. What does extended media mean in that context?

Seltzer:

It means bulk media. There are theories of what happens in very thin layers. For example. if you have an aluminum foil, you can do very well with analytical theory to say what happens. Because even with electrons, as I've mentioned, they change direction and energy very quickly. But if the foil is thin enough, you can use theory, and I've done it to do a reasonably good job of knowing what the energy and angular distribution of the transmitted electrons are emerging from such a thin foil. But now, if you say, "Well, how about an aluminum brick?" Well, that's an extended medium. That's much more difficult. Because we use, in electron Monte Carlo, this same analytical theory that tells you what the energy loss and angular deflection is for very short steps, the equivalent of these foils or films. But you have to keep stacking the steps. It's the same theory. But now, you've lost energy, you change directions, you might even come back the way you came from. No analytical theory's going to tell you that.

Well, I should be careful. They won't tell you very well. What I'm trying to say is, often, the energy-loss or angular-scattering theory assumes constant velocity. It's good for small energy loss, but if you lose a significant amount of energy, the assumptions in the theory are no longer valid. That's what we do in Monte Carlo. We sample from the energy-loss distribution, and then get a new energy, then we have a new distribution from the same theory. And we sample from that. So, in extended media, you've got a lot of energy loss and a lot of angular deflection. And you just keep following the histories until you've gotten to the site you're interested in, escaped, or its energy has fallen to a level you no longer care about.

So analytical theory can be and is used for the restricted, simple cases, but Monte Carlo is just perfect for complex geometry in extended media. Interfaces, such as aluminum here, silicon here. The histories look like steps you follow through the target. The coding is complicated. And the amount of time it takes the computer is somewhat increased by going through all this, but you can do it. I'm not aware of analytical theory handling such problems. The fundamental theories won't do it. There are other approaches, but I think Monte Carlo, as far as I know, is the best one for complex boundary and initial condition.

Zierler:

In 1988, were you the inaugural director of the Photon and Charged Particle Data Center? Or that preexisted your tenure?

Seltzer:

No, I did not start it. I think the first director, if I'm not mistaken, was John Hubbell, who I mentioned earlier. He was at NBS before I got there, I think perhaps by almost ten years. And he was working on the cross sections for what I call photons, you call x-rays, above one kilovolt up to a GeV or so. And he was remarkably successful with his work, collaborations with other theorists in other centers, and they developed an incredible robust body of cross sections. And along the way, these data were recognized as important data. And NBS wanted to benefit others, so they started data centers for people with extended data in various areas. He didn't do much work in charged particles, but it was called Charged Particle and Photon Data Center.

At some point, Martin Berger later became the director, and I'm trying to remember if it was when John Hubbell died or before. No, I think it was before he died. And then, Martin retired, and the mantle fell to me. I had worked with Hubbell a little bit, helped on early things. Of course, I worked with Martin a lot on electron and positron cross sections. This was all part of our data efforts. And much later, they decided to do away with data centers. Things started going online. I believe that might've helped with the demise of the so-called data centers. There was a management role for a data center where you disseminated your data. But with things going online, you really don't need that so much anymore. I'm assuming that was one of the reasons.

Zierler:

Was this coming at a point in your career where, generally, you were taking on more administrative responsibilities?

Seltzer:

Yes. It was. I don't remember feeling great about being in charge of the data center, but it was a source of funding that I didn't want to give up. There wasn't a lot of funding. Funding was always a struggle, so no matter how small the amount was, you never turned it down. But remember, we had a fifty-year history, or a little less, of data development and management. So, it wasn't like some new idea that came out of the blue. It was just picking up the mantle and continuing the funding. But at some point, funding stopped. Because of programs at Commerce and NIST, they just stopped supporting it, in which case you could administratively still keep the title, but it didn't mean much.

Zierler:

What was the funding important for? What research did you want to support with this funding?

Seltzer:

I'll be honest with you, for most of my career, in our division and all the groups, funding was necessary to maintain salaries and pay for equipment and travel. Funding was always a struggle. The ionizing radiation division had a history of fairly large fraction of other-agency funding. We talked about NASA funding, Office of Naval Research, Department of Energy, NCI. In my case, they were all rather small. But in other parts of the division, they could be rather significant. More recently, the Department of Homeland Security funding for mail irradiation or anti-terrorist device standards. So, with a large fraction of our funding from other agencies, the internal funding for our division had historically been rather low. And I don't want to say anything that is going to upset anyone, but NIST tended not to increase our funding as other agency funding diminished. And so, there were long periods of time in which it was difficult to maintain salaries. You had to fire people. You couldn't pay them. And programs dwindled and suffered somewhat. So, you looked for any other agency money you could find and often took on projects that weren't necessarily in the area that you would like to do your research in.

Zierler:

When you're talking about letting people go, you mean even federal employees? There were reductions in force during your time at NIST?

Seltzer:

Oh, yes. NIST has had a number of rounds of reductions in force. Some very public, where they would announce big budget cuts and RIFs. Now, of course, with civil service, there are always funny rules of bumping and appeals. But at some point, people go out the door. Your job might be abolished, but you can bump someone else if you're qualified to do their job, so they go out the door. But yes. I can't quote you numbers, but our division was larger than it is now when funding was much better. I don't know what else to say. And as a result, when I say we wouldn't give up funding, we didn't. We got involved partly out of patriotic duty, but after 9/11, all government agencies, I assume national labs as well, tried to figure out how to help.

We started getting involved in seeing what applications we could work with, and one was in writing performance standards for radiation-detection equipment and things like that. And so, we took on those projects. I worked on them as well. I was Group Leader, but when you go into an airport, and you throw your briefcase on the belt to be x-rayed, I worked on those standards. I helped develop them, such performance standards. Yes, you have to understand radiation. Don't misunderstand me. I'm not saying it's dry cleaning. It's radiation physics. Detectors for first responders, Geiger counters, portal monitors for trucks coming in, they could be laden with explosives or worse, nuclear material. Dirty bombs, what have you. So, we worked on all sorts of performance standards, not only NIST, but with the Department of Homeland Security and national labs trying to ensure safety. And for that, at least at the beginning, there was a good amount of money involved.

And so, it helped support salaries. We would then often not do that full-time, any particular scientist, so they could work on water calorimetry for absorbed-dose measurement and other things. But you had to work on the projects for the people who were paying the bills. So, it's not a perfect world. I'm sure it's not a perfect world in any area that people work in. Not just radiation physics, not just even science. You do what you have to when people pay you rather than lose jobs.

Zierler:

Six years later, your administrative responsibilities only grew when you became leader of the Radiation Interactions and Dosimetry Group. Was that also party motivated by funding and budgetary concerns? Or that was more just a good scientific opportunity?

Seltzer:

Oh, it was not a scientific opportunity at all. I had no ambition to be an administrator. Well, a manager; I had no particular ambition to be a manager. Like most of my work, I really didn't think I'd be good at it. I don't know that I was good at it, but I wasn't awful. Let me put it that way. I was senior in the sense I had been there quite a while. I was at a high pay level. And I understand that if you've got someone at a high pay level, you make them work for it, make them a manager. And I had years in at NIST. My colleague who was advancing to division chief and leaving the group leader position said he wanted me to be group leader. I can't say my arm was twisted, but one gets the feeling that you have to take such an offer. It won't be considered well if you just say, "No, I want to fiddle around at the bench and be a bench scientist." So, I did it.

In a sense, I thought it was my turn in the barrel, I'll put it that way. And I did it; I tried to learn management. I don't know that I was any better or worse than anyone else. I wasn't particularly good at bringing money in, but at that time, we had a lot of Department of Homeland Security funding, and it seemed to be okay. Funding became a problem later on as it always had been, but it became more serious. My wife was after me to retire. And I said, "I'll retire in a couple years." I think I wanted fifty years in the government. I had this goal, and I just enjoyed going to NIST. And I still did a little research, even though I was the group leader. I actually did a fair amount of research. I enjoyed that. But then, the budget got so bad that we lost a person, she had to go to another division. We just couldn't meet payroll. And there was one more person that would've been RIFed, so I just retired.

Zierler:

And it was really that zero sum, you retiring could save someone else's job?

Seltzer:

Well, I don't want to overstate this, but yes. In my mind, that's what it was. Now, I'm not saying he wouldn't have found another job at NIST. But I didn't want to put anybody in that situation. And it was time. My wife was after me to retire anyway. I figured, "All right, so I'll do it a couple years before I might've done it." Anyway, it's not bad. I got a great pension. I can thank the federal government for that.

Zierler:

For the last part of our talk, given that we talked about your more recent interests at the beginning, and we've worked all the way up to your retirement, I'd like to ask some broadly retrospective questions about your career, and then we'll end looking to the future. First, going back to the mentor relationship that you enjoyed with Martin Berger and how fundamental that was to the development of your career, as you moved into more senior and administrative positions, what opportunities have you seen to serve as a mentor in your own right to the younger generation of physicists and scientists at NIST?

Seltzer:

That's a very good question. I wish I had a really good or interesting answer. I have my own particular preferences for the sort of physics that I like. I remember, again, after 9/11, we inherited a number of scientists from other areas that maybe weren't so well-supported. And one scientist was actually doing, I thought, some very good work in fundamental science, and doing some measurements that possibly weren't being well supported. So, I said, "Do this Homeland Security work, but keep this other stuff up." I didn't mentor him, I just encouraged him because I just happened to like the science. It wasn't my area. It was lower in energy than anything I was working with. But I just thought it was good science. And as time went on, we had to hire some people to replace retirees. And I found a fellow, actually he was at Livermore, who was working in Monte Carlo. I was surprised he took the job, but I think his family wanted to leave California.

And so, he took the job in our group. I wouldn't say I really mentored him. I think I encouraged him, maybe pushed him in certain directions. I helped him on only an occasion or two. He more helped me, I think, than I helped him. And again, after some retirements, you have to replace people. So, I did that. I can't honestly say I mentored someone the way that Berger mentored me. I really can't say I've had that experience. I always felt I was at Berger's elbow. I don't recall anyone sort of being at my elbow. I remember getting involved in a number of things, sometimes doing things I thought contributed, but I'm not sure that the colleague on the other end felt the same- I was group leader, what could they say? I'm not sure they considered me helpful or a hindrance. But in some cases, I think it was reasonably successful. But I can't say I mentored them. I perhaps suggested different ways and worked on some different ways to help them, and I think in the end, it was reasonably appreciated. But I wouldn't say I was much of a mentor.

Zierler:

If you look back from the early days when you were a recent college graduate, and you didn't know what was going on to becoming a leader in the field, in what ways was the master's degree a part of that intellectual development, and to what extent was it simply checking a box because it was good thing to do for your career?

Seltzer:

Oh, I think I always wanted a graduate degree. I was already married. I was married a year when I got to NBS, had no children at the time. But I couldn't afford to go to graduate school with a wife, although I always considered that that's what I wanted to do. And as I said, I was taking courses towards a PhD. But then, I stopped and wrote a master's thesis. Now, the master's thesis was actually based on a lot of work that I had already done. Martin Berger was not formally my advisor for the master's thesis. However, he was my mentor, and he was an incredible amount of help. My formal advisor was Raymond Hayward, a physicist at NBS. He was actually pretty famous in his own right.

Ray was an adjunct professor at the University of Maryland, and he got a bit upset when I turned in my master's thesis. He was looking at it, and he said, "But isn't this stuff you were working on at NBS?" And I said, "Yes." He said, "Well, you're not supposed to do that. This is supposed to be original research." I said, "Well, it is original. I did it. But I did it also as part of my job." And so, he relented and said it wouldn't be a problem. At the time, I thought it was a very good piece of work. Looking back, I still think it was a very good piece of work. So, I think the synthesis of working at NBS with Martin Berger and going for a graduate degree was completed in that sense. It led to a graduate degree. Not the one, I guess, I originally thought I would get. But I think the thesis was PhD quality. I just never took the qualifying exam.

Zierler:

The ups and downs at the budgetary environment at NIST have been significant, as you've indicated. Do you attach those ups and downs to presidential administrations or Congresses? What might be some of the larger political trends that we can correlate with NIST's budgetary environment over the many decades of your career?

Seltzer:

I don't know that I'm expert enough to comment on that. My sense was NIST budgets do go up and down depending on administration. There was an Act a couple administration ago in which they were going to double NIST's budget over some years. It had a name I no longer recall. It started, but never completed. But we did see some good increases. I'm sure during tough times, there are some decreases. It depends. I don't sense that it's some antithesis on the part of a president, any individual, that says, "I don't want NIST. Let's cut their budget." I think it's budgetary pressures. I don't want to blame OMB or anything, but they have in mind what they need to do. Also, the budgetary process is odd. We don't just ask for money. At least at NIST, there are so-called budget initiatives.

To have to have an approved initiative, there's various monies involved to be shared by the researchers who will contribute to the goals. The initiatives get sent up to Commerce, where they might get whittled down, and then on to the Office of Management and Budget, where it might get whittled down again. If Congress approves it, the spending authority gets sent to NIST. NIST splits the money up to the various participants. But most of the sexy initiatives, the ones that make it, don't involve ionizing radiation. This sounds a little bit like complaining, but we were called on occasion to testify at Congressional meetings on the development of mammography standards, prostate seeds, and various radiation medical accomplishments. But ionizing radiation isn't high tech in the sense that are atomic clocks, atomic tweezers, and other more exotic physics, a good part of which are done at NIST. We've done some amazing things. But ionizing radiation isn't high tech.

So, we rarely are part of an initiative, we don't get a lot of new money, and that's one of the budgetary problems. I don't know that it's a particular animus. There was a time I think NIST management was tired of us complaining, and because of budgetary constraints, there was some talk, not in the too distant past, of, "What would happen if we just got rid of ionizing radiation?" But they decided it was an integral part of national standards. They did get rid of, years ago, dimensional standards. I think they handed it off to Oak Ridge. But they decided that they didn't want do that with ionizing radiation. But again, I don't know that it was any particular animus towards our program rather than just overall budget considerations. Everybody complains. Everybody thinks that what they do is important. I might say, "Well, gee, should we decrease the Department of Education budget." Of course, there are people working at the Department of Education who feel their programs are really important. And I understand that. We all think my program is more important than your program, and I understand that.

And so, it's hard. If we look at other countries, science is somewhat better supported. But we're doing pretty good science in the US, so I can't complain. But everybody complains about budgets. Also, private industry research has dwindled. IBM, Kodak, there were all these fundamental research areas supported, in some cases, lavishly, by private industry. You don't have that anymore.

Zierler:

Of course, in the case of Bell, you have a monopoly.

Seltzer:

Yeah, Bell Labs. You had some wonderful work coming out of all of this, and it's no longer the case. There's academic science, but even that's essentially funded by government because they go get government contracts. So, it's a different era. Like any old person, I always long for the good old days. I'm not sure the good old days were that good, but I think they were. Professionally, they were good. They were easier. I wasn't aware of a lot of budget constraints. But it didn't take me long to realize there were some. We didn't have so many rules and regulations, the workplace was freer, easier. So, I often wonder if things objectively get worse over time, and you're just there to see it, or whether I just get old and cranky. And I think the answer is both. I think things objectively are a bit worse in terms of professional careers. And, of course, I know I'm old and cranky.

Zierler:

As you well know, scientists can derive satisfaction in thinking about their contributions in two basic realms: the world of basic research, where you're just learning about how nature works, and in applied research, where you're focusing your efforts on addressing a particular problem or challenge that people or environments experience. To the extent that that's a binary that's useful for you in reflecting on your career, where do you see your key contributions? More on the basic research side or more on the applied side?

Seltzer:

I would guess, to be honest, more on the applied side. I had an ambition, throughout my career, of having a cross section named after me. Like, there's Bethe’s Theory. There's Einstein's Theory. I had a colleague in the Radiation Theory section, Leonard Maximon. He was a student of Bethe's, and there's the Bethe-Maximon equation. There are just all these named things. Oh, my original section chief was Ugo Fano. So, there's a Fano Factor. I wanted to develop something that could be named after me. And that, I guess, would've maybe been considered more basic. But other than carbonated water, I can't think of much that was named after me, and, of course, that came long before I did. Oh, and there's a funny anecdote. It was Martin Berger and Stephen Seltzer. And for decades, it was the work of Berger and Seltzer. And I always thought it sounded like sort of a menu item, Berger and Seltzer.

So, I would have to say applied. And again, I've been retired since 2010. It's already getting to be a long time. I recall being reasonably proud of my accomplishments as things went on and also being recognized. I'd go to international meetings, and people would want to meet me. I always thought, "Gee, that's nice." But the fact is, a lot of my work is now old. Some of it stands, I won't deny. But there's less of an immediate appreciation than it was at the time. So, things sort of get old. It's hard to be a famous physicist. I only knew a couple. And some of them might've been more famous in my mind. The world knows Einstein, but very few beyond him make it like that. I enjoyed working with some people who I thought were highly esteemed. And it was very satisfying to me. I tell my wife this anecdote. There's first-rate physicists who get a Nobel Prize. Ugo Fano got the Fermi Award from the Department of Energy, which is sort of a step down from the Nobel Prize. I'd say that's second tier. And that would make me, at best, a third-rate physicist. I'd always find that very amusing and humbling. Sometimes you do some work, and you might think it's fantastic, and nobody cares.

Other times, you've done some work, and thought it was pedestrian but good work, and everybody thinks it's wonderful. So, you're not always the best judge of your work. I enjoyed almost everything I did. And Monte Carlo development, I certainly played a role in. I wrote the code, but I have to admit, without Martin Berger, I don't think I would've ever done what I did. He was the driving force behind it. I wrote more than 6,000 lines of code for our Monte Carlo program. When I look back, that's a lot of code.

Zierler:

It is a lot of code. Last question, looking to the future, for the young generation out there that can't afford to be old and cranky, or who don't want to think that things are getting worse because you want to have optimism as you look ahead in your career, what advice would you give, and would you specifically recommend NIST as a great place for an aspiring young physicist to make a career?

Seltzer:

I would. I'm sure there are other agencies too. I'm obviously most familiar with NBS and NIST. I wouldn't feel that anybody should be discouraged. There was a brief time that my oldest grandson was actually thinking of physics, but then he decided mechanical engineering, and now, more recently, he wants to go into Wall Street Big Data, I guess being a quant; maybe it pays well, but I think he just likes the subjects. He's just starting out his freshman year. But I wouldn't discourage anybody from going into physics, and particularly, NIST is a good institution. There are the National Labs, there's academic research. I found physics particularly fulfilling. There were periods when I was very comfortable, but others not so much.

I remember when new PhD physicists were getting jobs driving taxi cabs. New PhDs just couldn't get a job. So, we've gone through tough times and good times. I think times are relatively reasonable now. I should mention, at the same time, a lot of them migrated to medical physics because there were no jobs in high-energy physics or nuclear physics during some of the bad times. But they still made use of their physics background.

I think NIST would be a good place. It has a combination of being a federal agency, but somewhat of an academic environment. So, it's a little like, perhaps, being at a university, but without all the backbiting. I don't know what your experience has been. But the protections in the civil service are considerable–obviously, a lot more bureaucratic than it used to be. But it's still, I think, a good agency to consider. And I would also tell them, "Enjoy yourselves, because thirty years from now, you're going to look back, and these are going to be the good old days." My good old days were the 1960s. Their good old days are going to be the 2020s.

Zierler:

Let's hope so. Let's hope the twenties are the good old days. Steve, it's been so fun spending this time with you. I really want to thank you for doing this and for sharing all of your insights over the years. I'm so happy that we connected. Thank you so much.

Seltzer:

Well, thank you very much, David.