Laurence Peterson

Zierler:

This is David Zierler, oral historian for the American Institute of Physics. It is November 4th, 2020. I'm so happy to be here with Professor Laurence E. Peterson. Larry, thank you so much for joining me today.

Peterson:

Thank you for the opportunity.

Zierler:

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

Peterson:

I am with the University of California at San Diego, and my title is Professor Emeritus of Physics. I retired from the faculty in 1994, it has been over twenty-five years since I have been an active faculty member. However, I continued on as the director of CASS, the Center for Astrophysics and Space Sciences, a position I held from 1988 to 1997. Afterwards, I continued on in a research position until about 2001. Since, I’d say I've been fully retired with no ongoing active research. But that doesn't mean I've stopped being interested in the sciences, and I have attended Scientific meetings, mainly APS meetings until 2017.

Zierler:

Larry, were you the founding director for the Center for Astrophysics and Space Sciences?

Peterson:

No, although I was heavily involved in the creation of the Center, the Founding Director was Margaret Burbidge who stayed on the first eight or nine years, then I was director until 1997, followed by Arthur Wolfe.

Zierler:

Larry, let’s start with your childhood. Tell me about your parents.

Peterson:

Actually, I'm going to go back one more generation. Both my paternal and maternal grandparents were farmers. My paternal grandparents came from Sweden, arrived in the United States about 1888, I would say. Eventually, my grandparents, Alfred and Maria, and their three surviving children settled a farm, in Burnett County in Northwestern Wisconsin. They had two boys and one girl. My father, the youngest child, bought the farm from his siblings when my grandfather retired from farming around 1930. I was born and lived on that farm until I was eight years old. Originally it was a Homestead type of farm. Are you familiar with the Homestead Act?

Zierler:

Yes.

Peterson:

Okay, well, they were Homesteaders (laughter), as I understand it, and the farm was in the Alfred Peterson family until 1939 when my parents lost it following the Depression and the Dust Bowl. My mother’s family, the Grants, were Irish; they came to this country a generation earlier than the Petersons. They left Ireland during the Potato Famine, went first to Canada. I don’t know much about how all that came about, but the second generation that included my Grant great grandfather and grandfather John Grant, left Canada in the 1880’s and came to the U.S., first in Michigan and then in Pierce County, Wisconsin, where my mother Mary was born. My grandfather, John Grant, eventually got a farm in Burnett County, Wisconsin where my mother and her siblings grew up. Both of my parents’ educations were in one-room rural schools. My paternal grandfather and my father were both farmers and blacksmiths. My grandfather had a regular forge, and my father inherited that. I remember being in my grandfather’s shop. He had a huge forge with a big giant bellows with an arm which must have been- I can’t remember exactly I was pretty young then—but it must have been about six or eight feet long, to pump the bellows. I could stand at the edge of the forge, reach up to grab the arm and ride it down as the bellows emptied into the forge. That’s one of the remembrances I have of my Grandfather Peterson. When they lost the farm, Grandfather Peterson went to live in Canada with his daughter, my aunt, and he died there during World War II. Now on my mother’s side, the Grants had a long tradition of teachers. That is, most of the Grants young women went on to a Normal school after Grammar School. It was sort of like a two or three-year college after grammar school. I guess you're familiar with what Normal schools were.

Zierler:

Sure.

Peterson:

Anyhow, after Normal school, my mother taught for about ten years in various places. Her last one-room school was right off of the Petersons’ property; it was actually the Grammar school my father had attended. This was in the mid to late 1920s. Then that school closed down, and a two room, a State Graded school, was built in a nearby unincorporated village called Alpha, Wisconsin. My mother was among the women who set up that school, which was only about a mile away from the Peterson farm. She was boarded at a neighbor farmer of the Peterson’s and that’s how she met my father. She was the local schoolmarm, as they called her, and my dad was an eligible bachelor. They were both late getting married: my mother was- well, she must have been twenty-eight, and my father thirty-eight. Now, my dad never completed Grammar school. It was a Swedish community, everybody talked Swedish and the story I heard was that he didn't get a Grammar school certificate because he didn't know enough English which is highly possible as I remember neighborhood gatherings where only Swedish was spoken. Now, I never learned Swedish but then or later, I was never very good at languages. At home, we spoke English as my mother did not speak Swedish. But every time my dad would go off to a neighbor, or we went to stores or something like that, it was always Swedish talk (laughter). My mother enjoyed teaching but gave it up when she married my father. She went back to it once us kids had left home. Even though she was not teaching, there were books around the house or books borrowed from the library. My maternal grandfather, despite a very limited education, loved reading, had books at his home and could quote a large amount of poetry from memory. He also loved history and I remember him listening to Churchill’s speeches on the short-wave radio during the few years he lived with us before passing. I have good memories of growing up with my family getting a balanced education: practical, mechanical from the Petersons, history, literature, current affairs from the Grants. One thing though, these Irish could not carry a tune, so we recited poetry rather than singing (laughter).

Zierler:

Larry, what kind of schools did you go to, growing up? Were they small schools?

Peterson:

Well, yeah. When we lost the farm in 1939- I say “we,” you know, because I'm talking about my parents, my brother, sister and myself, we had to move to a new county: St Croix County. Because we were moving around from one farm to another, I went to four different Grammar schools: one-room schools or the State Graded schools, before my parents bought a farm in 1944 and we settled in a place called New Richmond. It was a sad situation for my parents: unlike the original Peterson farm, these farms were not electrified or had piped water or central heating. Still, we all were glad to be on a farm we owned again. That is where I did the last year of Grammar school and my entire High school. I call New Richmond my hometown, even though my origins are someplace else. I feel I was lucky to attend Hight School there. The student body reflected the population around the school: farmers kids and city kids and from various European countries. The schoolteachers had the reputation to be better than in most High Schools around. I remember enjoying learning from all of them, well except the PE teacher. I was probably one of the worst coordinated kids he ever had to deal with. Despite my height, over six feet, I had no future in basketball: I could either run or dribble the ball but not both at the same time! During the High Schools four years, I had full courses of Math & Sciences, English, Literature and History as well as Shop. I believe I learned there the foundations of everything I leaned afterwards.

Zierler:

Larry, when did you start to get interested in science?

Peterson:

Well, it must have been fairly young. I don’t know about getting interested in science, but I got interested in mechanical activities. Well, every Spring, we had to get the machinery in order for the planting and the harvesting seasons and I, as the oldest kid, was always involved in that with my dad. I enjoyed taking apart machines, reassembling them, fixing gears and so forth. Around my sixth or seventh grade, one of my uncles went to Radio School as part of his military training and he gave me all his manuals and instructional materials. That got me very interested in radios and electronics. I collected old radios for their parts so I could construct new ones of my own design. Because of the radios, I then got interested in electricity. I built lots of electrical things then motors and devices to study and demonstrate magnetism and static electricity. For example, I made a gold-leaf type electrometer and wired-up motors and did what I could with batteries and magnets. In the last year of High School, I took an elective course in physics that expanded my interest to science in a broader sense. I could say I started with an interest in mechanical and electrical technologies that led me to science because I liked to understand the why and not just the how.

Zierler:

Larry, when you were thinking about college, what were your ambitions? What did you want to do with a college degree?

Peterson:

Like I said, I went to a very good high school. So, I knew I wanted to go to college to continue learning in all these fascinating disciplines. In addition to my high school teachers, I was lucky to meet Doc. Arnold. In New Richmond, there was a company called Doughboy Industries. Among other things, they made inflatable plastic toys which required advanced electronic sealing equipment. Right after high school, I worked for them full time during two summers and weekends the rest of time. My job was to help install and maintain these machines under the supervision of Doc. Arnold who had a PhD in Chemical Engineering. He became a mentor who helped me understand what I could learn in a university setting.

Zierler:

And Larry, where did you go for undergraduate?

Peterson:

Well, in my last year of high school, I was one of the top students of a class of 80. As such, I was entitled to a scholarship from the State of Wisconsin that would cover tuition and books at any of the State supported Colleges in Wisconsin. Because my parents couldn't afford to help me with the living expenses, I was on my own financially which limited my choices. My shop teacher was a graduate of a small college only about fifty miles away, called the Stout Institute in Menomonie, Wisconsin. There’s a story behind the name: basically it was founded by a Lumber Baron up in northern Wisconsin who could find lots of guys that could cut down trees, but not enough educated people who could set up sawmills and the infrastructure necessary for logging industry on a large scale. So, he founded a school which was basically an industrial arts education school. The Stout Institute was an obvious choice and almost the only way I could get into college. So, I entered into the regular program in the Fall of 1949. Sometime in the first semester, I realized this was really not where and what I wanted to study. I felt the level of education I was getting was lower that the level I had out of high school, and I wanted more. Also, these few months convinced me that I could take a regular academic load and support myself working part time. During the second semester, I applied to the University of Minnesota in Minneapolis, forty miles or so from my hometown. I was admitted there for the Fall of 1950 in the Electrical Engineering Program with an advanced standing, that is, some of the courses transferred from Stout to Minnesota. This meant that I would have only four years instead of five as an undergrad in the program. I had lots of electrical experiences at that point and actually knew a fair amount of electronics which I had sort of self-learned. Still, going from a small college with less than 1,000 students to a large University with over 30,000 students as well as with a much higher academic level, was quite a shock. I did adjust, enjoyed the learning and maintained good grades during the BS program. In addition, these years of interaction with a very diverse student body, considerably widened my horizon. I learned much more than science; I matured intellectually.

Zierler:

Tell me about the MS program you enrolled in.

Peterson:

By the last years of the BS program, I decided I wanted to continue my education by going on to Graduate School in Electrical Engineering which I started in the Fall of 1954. Then, the rules were that we had to have an Advisor and work either as a T.A or a R.A. or in one of the labs. Dr. W.G. Shepherd became my graduate advisor. He was a physicist who came from Bell Labs to the UofM to continue his work in an academic setting. The Department had a huge motor/generator type of lab, and at the beginning of my first year, I was tasked with creating a small electronic shop on the model of the Physics Department shop, which I had worked in as an undergraduate. More on that later. Afterwards, I worked in the labs of Dr. Shepherd doing basic research required to develop advanced electronic devices, basically an applied physics activity. I got a lot of experience in techniques such as high vacuum systems, glass blowing and clean room methods. These would be very useful for my future work. Although I learned a lot in the various courses I took, such as electromagnetism, network analysis, and communication theory, I realized that basic physics was the root of all these topics and came to the conclusion that I wanted to move to a PhD program in Physics which I did in the Fall of 1956. It was not an easy decision as I enjoyed working with Dr. Shepherd and his colleagues, specifically on an interesting developmental activity to improve vacuum tubes using secondary electron emission, which could have become a topic for a MS Thesis. Still, I never regretted my decision.

Zierler:

Larry, how did you come to work with John Winckler? How did that come about?

Peterson:

Well, that's another story. As I said earlier, I needed to support myself and the change from a Wisconsin College to the University of Minnesota meant that I lost my scholarship and was entirely on my own financially and that included paying an out-of-state tuition for four years. I did find a series of menial jobs and managed this way during the first one and half year . But I was looking for a job which was more to my liking in engineering or something related. I was lucky to get a job as a draftsman in the electronics shop in the Physics Department at the University. At first, it was just drawing circuits of electronic equipment used by experimental physicists. But pretty soon, I had enough knowledge and experience to actually design and build circuits. I worked on the Cosmic Ray Balloon activities of Professors Winckler and Ney. This is how I met John Winckler. One of my tasks was designing and implementing improvements of the telemetry system for balloon flights. Because of this experience, in the Fall of 1953, I was given the responsibility of the telemetry systems used on a Cosmic Ray expedition for balloon flights from the Galapagos Islands near the geomagnetic Equator. The flight operations were conducted from a Seaplane Tender. This was an amazing experience for me. I was very young: twenty-two years old, just off my third year of Electrical Engineering, and was entrusted with an important component of the balloon operation. It was also full of new experiences for me: I had never been more than about one hundred miles from home, crossing international borders, sailing the Panama Canal, traveling in an airplane and on an ocean-going ship. During my last year of the BS program, I earned my living working mostly in Winckler’s Cosmic Ray lab. So much so that, when during my second year of the MS program of Electrical Engineering, I made the decision to switch to a PhD program in Physics, I naturally went to him to review the possibilities. He helped me smooth the bureaucratic steps and I was enrolled in the PhD program of the Physics Department in the Fall of 1956. John Winckler was my Advisor and he provided me with a Graduate Assistantship and a Thesis topic. I graduated in the Spring of 1960. with a PhD.

Zierler:

Larry, can you explain how John’s research on aurora displays and solar flares influenced your research on emissions occurring beyond the solar system?

Peterson:

Well, that was when I was in Graduate School. Winckler had a balloon project for the International Geophysical Year, the IGY, which ran from 1 July 1957 to 31 December 1958. His contribution to the IGY was a series of balloon flights. The project was to study time variations of Cosmic Rays from measurements made at various altitude. I was assigned to this project and actually designed and built some of the equipment needed for the flights. We had about 80 of them, flying a simple ion chamber and Geiger counter to monitor Cosmic Ray variations. We did get a lot of Cosmic Ray data but we also, unexpectedly, discovered Auroral and Solar X-rays. I remember the first flight which was on the night of 30 June /1 July,1957. We flew out of a small airport, north of Minneapolis where we also set up the telemetry station. Winckler could not be with us, so I organized the assembling and testing of the equipment. John did join us on time for the flight. I was watching the telemetry when the counters started behaving erratically. I still remember watching the strip chart, and I thought something had gone wrong. But Winckler looked out and he saw a bright aurora, unusual at Minneapolis latitudes. He started called in to me: “The aurora is brightening” “Brighter aurora, dim aurora” and so forth and I marked his indications on the telemetry strip chart. So, the first discovery of X-Rays from Aurora was serendipitous. Still during the IGY in March 1958, we discovered, also serendipitously, a Hard X-ray burst from a large solar flare.

Zierler:

Larry, what’s the larger significance of that? When you were working with Winckler, at that moment, on the aurora? What’s the larger significance of seeing the X-ray from the aurora? What does that tell us more broadly?

Peterson:

Oh! I understand the question now. We were set to study Cosmic-Rays of Galactic origin, but the X-rays detected from the aurora were of terrestrial origin and the hard X-ray burst of 20 1958 was from the Sun. This emission from the Sun led us to speculate that other stars might also be emitting X-rays. The X-rays associated with the aurora implied that there were processes in the Earth’s magnetic field that accelerated electrons to high energies. These two discoveries opened a lot of potential fields of research. To answer and develop your question about the significance of the auroral X-rays , it showed that there were very energetic electrons, hundreds of kilovolts, which were associated with the auroral displays, precipitating out of the Earth magnetic field into the Earth’s ionosphere. There, the electrons were stopping, and exciting Nitrogen and Oxygen atoms to produce a visible aurora and also producing X-rays by the Bremsstrahlung Process. The main light of the auroral displays is at several hundred kilometers. Since the range in air of one hundred KeV electrons is much less than that of the X-rays they produce, the X-rays can penetrate the atmosphere to reach balloon altitudes, about thirty-five Km above the Earth’s surface. So, if we had any kind of a radiation detector at that altitude, it would detect the X-rays. But the real significance of that didn't come out until a little later. We and other observers made balloon flights to study auroral X-rays. But the whole story of where the electrons originated didn't get understood until Van Allen and his colleagues discovered the trapped radiation on the Explorer 1 satellite in 1958. That showed that there was a whole pool of energetic electrons trapped in the magnetosphere. If a magnetic storm happened and shook the magnetosphere, these electrons could spiral down into the upper atmosphere, and produce both the auroral displays and the X-rays associated with it. I continued working with John mostly on magnetospheric physics problems, but I was becoming more interested in following on the physics associated with X- rays and Gamma Ray emissions from Solar flares. I also wanted to research the production and transport of Cosmic Ray produced X-rays and Gamma Rays in the atmosphere as well as various detection methods, for example the scintillation counter techniques used in the 1960’s and solid-state detectors a few years later. To conclude the interpretation work on solar flares, in 1959, I was first author on a paper, Winckler and I wrote on the physical processes associated with the acceleration of particles in solar flares. The accelerated electrons produced radio bursts, and at the same time they precipitate into the Solar atmosphere and produce X-rays and Gamma Rays.

Zierler:

Larry, after you defended your thesis, what did you do next? What opportunities were available to you?

Peterson:

At Winckler’s suggestion, my thesis was actually a Cosmic Ray problem. The spectrum and the number of the various nuclear species in Cosmic Rays was a big issue at that time. To get the data needed for my thesis, I built an instrument to measure the high-energy part of the helium nuclei (alpha particle) component of the Cosmic Ray spectrum. Winckler knew that the Office of Naval Research (ONR) was organizing an expedition to Guam to fly balloons with Cosmic Ray experiments near the geomagnetic equator. John submitted a request, which was accepted, to fly my instrument as part of that program. I used a combination of a Cherenkov counter and a scintillation counter to separate the charge components. The East-West effect of Cosmic rays due to the Earth’s magnetic field gives data points on the high energy spectrum of the Alpha particles. The collected data allowed me to determined points on the energy spectrum of Alpha particles. For a short time, it was the highest energy point on this spectrum. But of course, better balloon instruments came along, as well as satellite instruments and my results were soon superseded. I worked very hard on this experiment. As a grad student, in addition to working on my thesis, I was working on the problems of detecting X-rays from the Sun and from space. After I defended my thesis in June 1960, Winckler offered me a two-year post-Doctoral position to continue this research activity. There were two sides to my work: the first was developing techniques to measure X-rays from space using balloons and spacecrafts. My second responsibility, with the help of a team, was to build an X-ray and Gamma Ray astronomy instrument for OSO 1. NASA had started a program to measure particle radiations in space. Winckler got involved in that activity and through it, into the Orbiting Solar Observatory (OSO) program. At the time, the last year of my graduate studies, I was trying to understand what had to be done to detect extra-terrestrial X-rays. Well, somehow, I had the dim idea that, if the sun can produce X-rays, why can’t the rest of the objects in the universe? I didn't know much about astronomy then, I read up on the subject, there were things called Supernovae and radio stars and so forth. I figured that, since the solar flares produced radio bursts as well as X-ray bursts, well, maybe some of these objects might also produce them. And there were of course Cosmic Rays, but nobody really understood where and how they were accelerated. John encouraged me to submit a proposal for an X-ray and Gamma Ray instrument on the OSO -1, which was accepted.

Zierler:

The question is, Larry, what more did you do after you defended your thesis? What was your next move?

Peterson:

Early 1961, I started to look for a more permanent position to continue this research. This happened through John ‘s network and the one I had developed during the construction of the OSO-1 instrument which required a lot of interactions with scientists in many institutions. I got feelers from NASA’s Goddard Space Flight Center where I knew two alumni from the UofM Cosmic ray group, Princeton, as well as Colorado, Caltech and UCSD. The last three actually interviewed me. I chose UCSD because they basically gave me carte blanche and a tenure track position. I could work on my own research projects which was not the case of the other offers. Another factor was the weather: when I came for my interview, I left Minneapolis in a blizzard situation and landed in warm and sunny San Diego, welcomed by the founding Chair of the emerging Physics Department, Keith Brueckner, dressed in a short sleeve shirt, shorts and sandals! He took me to the Scripps Institute of Oceanography, where the Physics Department was then located, and set me on a bench to see the surf and the sand of the ocean shore. The decision was easy! (Laughter) After I arrived at UCSD, Keith told me of the circumstances of my hiring. When it was decided to add a Space Physics activity to the Physics Department, Keith, who had many contacts, called Van Allen at Iowa for a recommendation. Van Allen suggested his student, Carl McIlwain and Larry Peterson at Minnesota. We were both hired.

Zierler:

What were the findings of the experiment OSO 1?

Peterson:

Well, OSO 1 produced a lot of data but the results from my instrument were disappointing. We did detect a number of solar flares with type three radio bursts, however for me the experience I gained in implementing an instrument flying on an orbiting spacecraft was one of the positive consequences. Although I designed and built the detectors, the electronic system and the supporting structure were designed and built by Bob Howard, the head of the UofM Electronic shop at that time, a man I respected a lot and was a close colleague. Another important result was a better understanding of the effect of Cosmic-Rays producing background in X- and Gamma ray detectors. I wrote a long paper on these effects which was never published because it fell in the crack between scientific results and instrument description. I did circulate it as a report to other scientists beginning to work in the field and it was often referenced in the following years.

Zierler:

And Larry, was the plan for you to continue on with your collaboration in Minnesota, even when you moved to San Diego?

Peterson:

Well, actually, I made a deal with UCSD. My goal was, in retrospect, pretty single-minded: I wanted to follow through on the possibility of detecting Cosmic X-rays. Of course, nobody had a such a program, because Cosmic X-rays had not been yet discovered. They were discovered on a rocket flight by Ricardo Giacconi and his colleagues in June 1962, months before I moved to San Diego. The discovery motivated me a lot. When I left Minnesota, Winckler generously, let me take all the OSO-1 data that needed to be analyzed as well as some of the equipment, like a balloon test gondola, etc. This meant that I had to build a team as soon as I arrived at UCSD. These were exciting times for me: I was establishing myself as an up-coming scientist in the new promising field of space astronomy and at very young University. Also, Space Science was getting recognized through NASA’s programs. Even though Winckler and I had been co-PIs on the OSO-1 experiment, I was the one that put it together and made it work through launch. This is why it made sense that I took the data with me to California. This lead me to form the X-ray and Gamma Ray astronomy group. I had three research activities in mind: establish a balloon activity to study detector technologies and possibly observe Cosmic X-ray sources. Then there was the data analysis from OSOS-1. Lastly, I wanted to develop a new Cosmic X-Ray instrument to fly on an upcoming OSO flight. I was well used to analyze a few hours of data from an occasional balloon flight, but satellite data comes down in droves. While still in Minnesota, I remember the first orbit of the OSO-1 data, I had an undergraduate student reading the chart, and it took him a week to read one orbit of data. Meanwhile, one hundred orbit of data was accumulated from OSO-1. I realized that we had to put together some sort of a computer-driven electronic device to handle the incoming data which came in a semi-analog form. I had an engineer I worked with at Minnesota develop a device that digitize the data stream. But it really didn't work very well and wasn’t capable of handling the amount of data we had. When I got to UCSD, one of the first task was to build an entirely different data reduction system based on a different concept. So, I hired engineers from the Convair Scientific Research lab. I got a very talented computer programmer, Louis Huszard, who had worked on the Illiac as an undergraduate at the University of Illinois. He really understood data systems and how to put them together. It was also common knowledge in the group that I knew quite a lot about electrical and electronic engineering which helped the dialogue between us. We put together a system for converting analog data to digital magnetic tapes which were brought to the CDC main frame computer for processing. The computer operators would run the data overnight and the next morning you got a print-out or another magnetic tape, depending on the application. I remember a colleague who was working on some space data. He put his card deck in and data tape for overnight processing, and the next day, he got this printout which reach the page limit (laughter). He got thirty pages saying “error, error, in subroutine such and such.” He said, “I had never been told that he was wrong so many times in all his life” (laughter). There were a lot of things like that that happened to us, too (laughter).

Zierler:

Larry, can you talk a little bit about the detection of cosmic photons? When did that come about?

Peterson:

The detection of X-rays and Gamma Rays is based on the understanding of their interactions which happened over the early decades of the twentieth century. Well, first of all, to detect a photon, you have to convert it to an electron which can be detected, and its energy determined using techniques of nuclear physics. Depending on its energy, the photon interaction will either produce a photoelectron in the KeV energy range or a scattered electron due to the Compton effect. The Compton effect is not ideal for detection because much of the energy goes in the scattered photon not in the electron which stops in the detector material. Now, at higher energies, above several MeV, the photon produces a positron-electron pair. All Gamma Ray astronomy, above about twenty MeV, is done by using the pair effect. Above about twenty MeV, the pairs diverge enough to follow the tracks and determine the direction and the energy of the original Gamma Ray. The Fermi observatory, which was built at Stanford and is now in orbit has produced all kinds of nice, fascinating results on high energy Cosmic Gamma Rays.

Zierler:

Larry, can you talk a little bit about the impact of Sputnik and the subsequent creation of NASA on your research?

Peterson:

The impact was enormous. I would say Sputnik, and the Space Age which followed, opened up for research the entire electro-magnetic spectrum of the Universe, rather than through the narrow windows allowed by the atmosphere. New astronomies were possible, including that of X-ray and Gamma Rays. Many other fields, such as magnetospheric physics and Planetary exploration were now possible. When NASA was created by the Eisenhower Administration in 1958, one of its first decisions was the creation of many satellite programs for scientific research, including the Orbiting Solar Observatory program.

Zierler:

Larry, what was your involvement with the development of the OSO 1 instrument?

Peterson:

We might have touched on this subject earlier. Anyhow, the first space instrument I designed and built was aboard OSO-1, was launch in 1962. I was still in graduate school when the project started so Winckler was the official PI and I was listed as a Co-investigator. In the early sixties, I remember going to Boulder where the spacecraft was being built, to attend the first meeting of the instrument teams. I don’t remember Winckler going to these various project meetings. It was for me a pretty exciting period, because I had my own projects going under Winkler’s wing. In addition to building the OSO 1 instrument, I was testing various X-ray and Gamma Ray detectors on balloons to determine their properties in the Cosmic Ray radiation environment.

Zierler:

Larry, in what ways, when you got to San Diego, did the high-energy astronomy group expand?

Peterson:

It didn't exist. I started the High-Energy astronomy group.

Zierler:

Right.

Peterson:

My choice of going to a starting university was a bit of a gamble, but the Physics Department gambled too. They gave me labs and office spaces and allowed me to hire people. As soon as I was accepted by UCSD, I consulted with people I knew at NASA Headquarters - particularly Nancy Roman, and John Naugle, who suggested I submit a proposal to NASA, the attribution of a research grant. I used those funds to start hiring people for my project and that was the start of the group.

Zierler:

Larry, how did you develop the balloon program? How did you, literally, get that off the ground?

Peterson:

Actually, the initial proposal submitted to NASA through UCSD – as mentioned in the previous answer - had three components. One was a balloon program to develop detectors and make observations for solar and Cosmic X-rays. The initial funding, I received was for the balloon project. But what helped me most was a lucky coincidence happening at the San Diego Convair Scientific Laboratory -CSRL- and more specifically its balloon operation group. I knew some of the people there who had come from Minnesota. They told me that the group was about to be disbanded for lack of internal funding. So, I, through UCSD, contracted with Convair for half dozen flights which happened in the Summer of 1963, in the desert of Arizona. Some months later, I picked up some of the Convair equipment to form my own balloon operation group. We actually had five trucks, one of them was converted into a telemetry van, another one was used to haul the many bottles of helium to the launch site, a third one carried the launching equipment. The other two were used for general transportation of people and equipment. Somebody called the trucks the “Great White Fleet” because they were all painted white. Anyhow, launching the balloon, tracking it and recovering the equipment not always where we expected, was an activity which was fun and adventurous. We set up our operations in the Arizona desert with our telemetry van and launched the balloons near a place called Dateland. This was not a large city, we used to joke that the sign Leaving Dateland was on the back of the sign Arriving in Dateland! From there we could track the balloons westward and usually would recover the equipment in the Imperial Valley in California. In the Summer 1964, for the second and following seasons of balloon flights, we used the then newly created balloon launching operation facility that the National Center for Atmospheric Research (NCAR) had established at Palestine, Texas. In the following decades, we totaled about eighty balloon flights. Not all of them were flown from Palestine, a few were launched from various field stations established by the National Scientific Balloon Facility (NSBF) in the U.S., Alice Spring Australia, McMurdo Sound in Antarctica. While a lot of these flights were used to make observation of Cosmic X-ray or Gamma Ray sources, many others were to test detector concepts and to understand the nature of the physics of the X-ray background in the Cosmic Ray environment at balloon altitudes. The background at balloon altitudes is very similar to the one existing in a spacecraft. Understanding the physics of this background was essential to the development of advanced instruments for detecting Cosmic X-rays and Gamma-Rays in space. Some of these flights were also testing engineering models of a detector system before committing them to a space mission. The balloon activity was an essential adjunct to the space-borne experiments of the group. Some of my PhD students used the balloon results on X-ray and Gamma Ray background for their thesis.

Zierler:

Larry, when did you get involved in advisory work for NASA?

Peterson:

It was not long after I arrived at UCSD that I got invited to be a member of the Solar Physics Subcommittee. This was part of the NASA internal advisory structure. This structure was changing with each different congressional budget authorizations. The chair of these committees was usually a leading scientist at a non-NASA institution. The first meeting I attended was at a National Observatory in Tucson probably in 1966. I enjoyed being on this committee mingling with the leading scientists in the field and listening to the banter going on between the members on the important scientific problems in solar physics. This first experience was very important as it was an opportunity to hear and speak of a discipline that had not attracted many scientists yet, and to learn about the broader aspects of solar physics. It was a good learning experience for me. From then on, I was almost constantly on some NASA Internal Advisory Committee until my retirement. Additionally, I was invited to participate in a number of NASA Summer Studies in the late sixties and early seventies. These studies were of a broad disciplinary nature which included various branches of astronomy, planetary exploration and other space physics activities. I was usually on a sub-group for High Energy Astronomy. These meetings often had plenary sessions where the various disciplines presented the conclusions of their work. Because of my participation to many internal committees, I was somehow invited to be a member of the National Academy of Sciences’ Space Science Board. The Board was charged to oversee and comment on NASA’s space sciences activities. Members of the Board were often also liaison to similar committees in space faring countries. As part of this activity of the Board, I was nominated to be the U.S. Vice-President of an international Committee called COSPAR or Committee on Space Research, established under the umbrella of the International Council of Scientific Unions (ICSU) as a place where scientists from all over the world, including from the Eastern Bloc - could have exchanges. In those days, COSPAR was directed by a President traditionally from Western Europe and two vice-presidents. One was nominated by the US Space Science Board, the other one by the USSR Academy of Sciences. I served as the US VP from 1980 to 1986. In this capacity, I met and worked with many internationally known scientists in many different space related disciplines. This was a mind opening experience. It also provided me with international scientific contacts and exchanges as well as a taste for National and International Scientific meetings. Two more of this kind of activities come to my mind. For over three years, I was on the oversight committee for building the Keck telescope on Mauna Kea. It gave me insight into the design and operation of a large optical telescope. The other such activity was as a member of the external Visiting Committee for the Max Planck Institute of Extra-Terrestrial Physics in Munich. There, I was in contact with many non-U.S. scientists and I gained insight on how European organized their research institutions. The reunification of Germany happened during my period as a member. As a result, our committee was invited to go and review several astronomical research facilities in the former East Germany. Quite an experience!

Zierler:

OSO 3, how did that come into development?

Peterson:

The Orbiting Solar Observatory, OSO, series was conceived by NASA in the late 1970’s. Each spacecraft contained a section which could point at the with arcminute accuracy for ultra-violet and extreme UV spectroscopy, and a more massive stable platform to mount these pointed instruments. This platform could also contain other non-pointed instruments. The spacecrafts were built, integrated, and tested by the Ball Brothers Research Corporation in Boulder Colorado (BBRC). Eight spacecraft were built and launched before the series was terminated in the late 1970’s. As you know, I built my first spacecraft instrument for OSO-1. I think, I also mentioned earlier that in my first proposal to NASA in early 1961, to obtain funding for my UCSD program, there were three activities, one of them was for an instrument on a follow-on OSO, that ended up being on OSO-3. Exactly how the experiment was selected is unclear as the elaborate proposal review and selection by a committee for spacecraft instruments was not yet in place. I received the news of the selection soon after arriving at UCSD, long before I had the in-house capability of building an instrument for a spacecraft. So, I subcontracted with BBRC the instrument design, construction, test and integration into the spacecraft. The discussions about the contract and its terms with NASA and BBRC was a new experience both for the UCSD contract office and me. My first encounter with this level of rules and legalese! The goal of the experiment was to determine the spectrum and time variations of hard X-rays from the Sun and possible Cosmic sources. The instrument consisted of an active anti-coincidence collimating shield and a sodium iodide scintillation counter to detect the in-coming X-rays. I did the conceptual design on the instrument based on the experience accumulated with OSO -1, and on the results of my balloon studies at Minnesota. I kept tight control over the detailed design and construction by BBRC. The OSO-3’s first launch in October 1965 failed due to a malfunction of the third stage of Thor/Delta rocket. The spacecraft was rebuilt, and spare instruments incorporated in a new spacecraft launched in March 1967 still under the name OSO-3. Before the first launch, I had hired a postdoc from UC Berkley named Hugh Hudson, to work on the data analysis. Between the first and the second launch, Hugh contributed to the balloon program. Because the OSO-3 data arrived partially reduced on magnetic stapes, the analog to digital conversion system set up for OSO-1 analysis was not needed. The data tapes could be fed directly to the UCSD computer system for analysis. The experiments produced many new results on hard X-rays from solar flares and on the spectra and time variations of Cosmic X-rays from known sources already discovered by rocket observations. Three of my students received their PhDs from the analysis of this data. One more thing about the Thor/Delta rocket. The Delta rocket system had a rocky history as far as third stages were concerned. So finally, they integrated the third stage of the Thor system with the Delta rocket. Then it was more self-sufficient and reliable system. It was a great rocket that you could re-ignite once it was in orbit and change its orbit plane and things like that. Anyhow, the Thor/Delta system was the one which all the rest of the OSO’s and dozens of other spacecrafts were launched, and it’s still a very active launching system. In 2004, during a visit to Florida with members of my family and two grandsons , in addition to the NASA part, we toured the Air Force part of Cape Canaveral. We had to get pre-authorized as it included a lot of classified areas. To my pleasant surprise, we got close to the launch facility for the Delta system. and the original hangar we used for OSO-1 was still there, over forty years later. It was great to be able to show the hangar to my grandsons and say, “grandpa worked there.” For me, it was sort of Old Home Week (laughter).

Zierler:

(Laughter) Larry, what were some of the most significant things you were learning from the balloon program as you were studying cosmic X-ray sources?

Peterson:

The balloon program at UCSD produced results in two categories. One was the development of detector technologies and the second was observations of strong X-ray sources. In the technology area, balloon flights data showed that Cosmic Ray interactions in high Z materials produced more X-ray background than was absorbed from external sources. This meant materials such as lead would not work well as a background shield and a collimating system. We continued the development of the active anti-coincidence collimating shield using CsI in many different configurations. This knowledge was used in the design of instruments we flew on later balloon flights as well as OSO-3 and -7 and, later on the High Energy Astronomical Observatory – HEAO. We also developed a model of the production and transport of X-rays produced by Cosmic Rays in the Earth’s upper atmosphere. We called it the Semi Empirical Model. Concerning our observations, in the mid-sixties, we used an engineering model of the OSO-3 detectors with a modified data system and mounted it on a balloon pointing system to make observations of strong Cosmic X-ray sources. This allowed us to determine the spectrum of the Crab Nebula and showed that the X-rays were likely produced by non-thermal processes. We also measured the spectrum of Sco-X1, this showed the X-rays were likely produced in a hot gas of 50 million degrees. Later authors credited these discoveries, along with those of George. Clark of MIT, as giving birth to the field of hard X-ray and low energy Gamma Ray Astronomy. We also measured the spectra and short-term time variations of sources such as Cyg X-1 as well as the extra galactic source NGC 4151. In conclusion, I believe the group balloon activities, in addition to forming a central basis for spacecraft instruments designs and operations, contributed important results and discoveries that advanced X-ray astronomy and laid the foundation for low energy Gamma Ray astronomy. I have had the pleasure of noting that many instruments, developed by experimentalists across the world, were based on techniques developed by my group at UCSD.

Zierler:

Larry, how was the search for Gamma Ray lines going at this point?

Peterson:

My interest in Gamma Ray lines and their spectroscopy occurred during the summer of 1956 when I was transiting between Electrical Engineering and Physics. I spent many mornings reading articles in the Review of Modern Physics to get up to date on the latest in Physics. One of the papers I read was the landmark paper by Burbidge, Burbidge, Fowler and Hoyle on the nucleosynthesis of the elements in stars. After taking a course in Nuclear Physics, I agreed with the idea that there should be isotopes in the Cosmos decaying and producing Gamma Ray lines and it became a quiet goal of mine to detect Gamma Ray lines from these processes. In the late fifties, there were only speculations. Once at UCSD, I charged my first Graduate Student, Bud Jacobson, to do a search for Cosmic Gamma Ray lines using a cooled Germanium detector in an active anticoincidence collimated shield left over from OSO-3. The cooled Ge detector had a much higher energy resolution than that of a scintillation counter. It had been suggested that the sixty-day decay of the light curve after a supernova might be associated with a decay of Cf 254 which has also a similar half-life. If that was the case, there should be many longer -lived isotopes still decaying in the nebula and producing Gamma Ray lines. Searching for these possible lines was the prime subject of Jacobson‘s thesis. For this possibility, Jacobson searched the Crab Nebula, a remnant from a supernova occurred in 1054. He did not detect any of the predicted lines. It was soon pointed out that the Cf 254 hypothesis for the light curve did not meet other astrophysical requirements and was incorrect. Much later in the mid to late seventies, other investigators did measure the 0.51 MeV Gamma Ray line from the Galactic Center due to positron electron annihilation and also from various nuclear reactions produced by accelerated protons during solar flares. This news encouraged me to resume building an instrument of much greater sensitivity to detect and search for Gamma Ray lines in other objects in the Cosmos. The instrument, HEXAGONE, had an array of large volume cooled Ge detectors in an active anticoincidence collimated shield. It was flown on a balloon flight launched from Texas. It verified the concept and produced new results on the 0.51MeV line because it had a better spatial resolution than previous instruments. We then formed an international collaboration to propose an instrument on the up-coming Gamma Ray Observatory (GRO). It was accepted but after phase A studies the instrument was remove from the GRO instrument array due of its cost and complexity. This was very disappointing to me and ended my direct involvement in the Gamma Ray lines search. A member of the group flew the instrument in late 1988 on a balloon launched from Australia to measure Gamma Rays associated with the 1987 A Supernova. We were hoping to detect Gamma Rays from the Ni- Co Fe decay chain. The results were disappointing. However, the HEXAGON instrument concept was used later on the US High Energy Solar Spectroscopy and Imaging mission ( RHESSI) and on the ESA INTEGRAL flown in 2002.

Zierler:

What about your work on Solar Gamma rays? What were you learning about solar gamma rays at this point?

Peterson:

Following detection of hard X-rays from the 20 March 1958 solar flare, I became interested in the possibility of detecting Gamma Rays, also being produced by energetic particles in the Solar flare. A colleague of mine at UCSD, Richard Lingenfelter and his collaborators had made more substantial theoretical predictions of the possibility of Gamma Rays produced by Solar flares using new data on energetic protons and electrons emanating from the un in interplanetary medium. This led me to propose a Gamma Ray instrument for the up-coming OSO-7 spacecraft. My experiment was not selected but a similar experiment proposed by Ed Chupp at the University of New Hampshire was. His instrument was very similar to the one I proposed, but he made a more clever use of the spacecraft resources. Actually, when I read about the proposal I thought “why did I not come up with this idea!”! His instrument measured the 2.2 MeV line due to deuteron formation in the Solar photosphere and additional measurements of the 0.51 MeV line due to positron-electron annihilation during the intense Solar events of July and August 1972. Later instruments on spacecraft, particular the HESSI that I mentioned earlier, detected more events of Solar flares emitting Gamma Rays, giving a much more complete understanding of the acceleration and transport of energetic particles in the Solar flare region . Even though I was no longer a direct contributor to these measurements, I remained interested in the subject.

Zierler:

Larry, how did the ERS series come about?

Peterson:

Oh, that was a diversion from my planned program. I knew a scientist named James Vette who was at the Convair Scientific Research Lab where he had initiated the balloon activity. He had left Convair to go to the Aerospace Corporation in Los Angeles just before I came to UCSD. Sometime, probably early 1964, I got a call from him on a possible opportunity for placing a Gamma Ray instrument on a space mission. TRW had developed a small spacecraft called the Octahedral Research Satellite - ORS. This was a cute little spacecraft made of triangles about a foot long on each side. Each panel was covered with solar cells and two antennas were sticking out from opposite corners. It was launched from a canister located on top of one of the upper stage of the rocket, under the main payload. I liked the opportunity because the small mass of the spacecraft prevented buildup of background due to Cosmic-Ray interactions and I could include a scintillation counter, so the active detector material was a large fraction of the total spacecraft mass. These were scheduled to be launched with the Vela satellites which were designed to detect clandestine nuclear test explosions in space. Most of these activities were highly classified but the ORS was not. However, I did not know much in advance the dates of the launches. When a Vela launch was imminent, Jim would give me a call to get our detectors to TRW for integration into the ORS spacecraft. I could detect the urgency in Jim’s telephone calls and visits, like “Well, maybe you’d better get your detector up here pretty soon, or it’s going to be left on the ground.” The two ORS I had an instrument on were designated as Environmental Research Satellites (ERS) and launched one in July 1965, and the second in March 1967. To be clear, Environment in ERS meant the energetic radiation environment which needed to be understood as it damaged satellite systems. Each of the two ERS’s operated several months before either failing or being turned off. Data from the spacecraft was recorded by various tracking stations worldwide and raw tapes were sent to UCSD for reduction and analysis. We used the system originally made for the OSO-1. Also flown in the spacecrafts, there were a number of energetic particle detectors from other research labs. The Vela program was managed by the Air Force. They contracted us to reduce the data of all detectors on board and present it as graphical charts. I had a crew of four or six undergraduates playing back the tapes and digitizing them. I never really understood the reason for these graphical charts except maybe it was show and tell for the Air Force guys. I never knew quite what went on behind the scenes, of course. In participating in the ERS program, I was hoping to get more information on the spectra of the so-called diffuse component of Cosmic Gamma-Rays. This component had been detected by previous X-ray and Gamma Ray instruments and seemed to come uniformly from all directions in the sky with no specific source. The ERS main results from my point of view were new and extended measurements of the defused component.

Zierler:

Larry, what were some of the major advances in lunar and cosmic nuclear Gamma Rays through the Apollo program?

Peterson:

My involvement in the Apollo program happened through James Arnold. He was a cosmo-chemist who came to UCSD from Chicago in the early 1960’s. He was one of the founders of the Chemistry Department and later Dean of the new and expanding Science Departments at UCSD. As such, one of his responsibilities was to review and sign off proposals from the various Departments. When the proposal I submitted prior to my arrival in San Diego crossed his desk, he noted with interest my program in Gamma Rays. He also had an interest in using Gamma Ray emissions from planetary surfaces to understand the origin and evolution of planets including the Moon. He had already flown a spectrometer on one of the Ranger missions to the Moon. The Rangers were supposed to provide a survey-map of the Moon’s surface in advance of the Apollo landings. Ranger 3 failed before reaching the Moon but measured a flux in cislunar space, which is now identified as the Defuse Component of Cosmic Gamma Rays. Quite a controversial discovery at the time. Jim was heavily involved in planning the science program associated with the Apollo missions to the moon and had managed to have a Gamma Ray spectrometer placed on the Service Module of the Apollo system which would orbit the Moon during the landing and could therefore map the Gamma Rays emitted from the Lunar surface. Soon after I was established at UCSD, Jim and I had many discussions of this experiment. We decided a new improved spectrometer was needed. I designed it based on a NaI scintillation counter and constructed it as an engineering model. We flew it on a balloon to determine its performance, then it became the model for the spectrometers to be flown aboard the Apollo 15 and sixteen Missions, they were built under the supervision of the Jet Propulsion Laboratory - JPL. The spectrometer was mounted at the end of a twenty-five-foot boom which could be extended from the Service Module and could be ejected in case some event happened which endangered the Astronauts. I was in charge of monitoring the spectrometer during the passage between the Earth the Moon. Then Jim Arnold took over. To provide additional information on the surface of the moon, there was a second instrument aboard under the leadership of Jack Trumbka from the Goddard Space Flight Center, to detect Lunar X-rays. Both teams were located in the same Support Room next to Mission Control. From these missions, Arnold and his colleagues at JPL, Al Metzger and Bob Reedy, got a map of K40 and Th 228 from the Lunar surface. These isotopes are important for understanding the chemical evolution of the Moon. For my part, I got an additional measurement of the diffuse Cosmic Gamma Ray flux that extended the spectrum measured with the ERS, as well as a serendipitous measurement of the spectrum of a Cosmic Gamma Ray Bursts, a GRB, this was the first complete spectrum of a GRB.

Zierler:

Larry, how did OSO 7 come into being?

Peterson:

Well, the OSO-7 was part of the ongoing OSO program. I had been on several committees evaluating and selecting instruments for the various OSOs as part of the activity of the Solar Physics Subcommittee and its follow-ons. When it came to evaluate the experiment complement of the upcoming OSO-7, we had a good choice of instruments for the Solar pointed part of the OSO, but for the rotating inertial platform, also called the wheel, the choice was rather dismal. NASA recognized this and issued a second Announcement of Opportunity, specifically requesting instruments for high energy astronomy. I proposed three different instruments, one to study Solar X-rays, one for Cosmic X-rays and a third for Solar Gamma-Ray line emissions. Of course, I was not on the second instrument evaluation committee, but two of my proposals were selected: the Solar instrument and the one for Cosmic X-rays.The third was competing with a similar instrument and mine was not selected. More on that later. The OSO-7 was launched in September 1971. The Solar instrument produced lots of new information on the spectra and time structure of Solar X-ray bursts in the 10 KeV range and had a much greater dynamic range for intensities than the instrument on OSO-3. The Cosmic X-ray instrument measured the spectra and time variations of many Galactic and Extragalactic objects in the hard X-ray range above 7 KeV, and made significant measurements of the spectra and time variations of binary X-Ray sources. For each of these instruments, I had hired a Postdoc early enough in the program to participate in the final tests and calibrations before launch, and to work with the graduate students on the data analysis.

Zierler:

Larry, what was needed at this point with regard to the HEAO?

Peterson:

In the early seventies, it became evident that important advances were being made in X-Ray, Gamma Ray astronomy and in Cosmic Rays. There was also an emerging community of scientists ready to create instruments for spacecraft in the hope of making advances in the new field of High Energy Astrophysics. I was on a number of committees and boards giving recommendations to NASA for the composition of a new program in High Energy Astrophysics. NASA issued an Announcement of Opportunity for Instruments on a new Spacecraft series called the High Energy Astronomical Observatories (HEAO). I proposed a fifteen KeV to ten MeV Hard X-Ray and Gamma Ray instrument for this mission. It was excepted by NASA and funded for a preliminary Phase A study. The original HEAO program consisted of two large spacecrafts containing many experiments. The cost and complexity of the proposed missions essentially broke the budget and the PIs received phone calls from NASA in January 1973 saying the program had been canceled and was about to be restructured into a program of three smaller spacecrafts with fewer experiments. I contacted Walter Lewin of MIT who also had a displaced instrument on the original HEAO. We formed a collaboration for a modified UCSD /MIT instrument which essentially included the objectives of his original experiment. This new UCSD/MIT instrument was a cluster of about seven NaI scintillation counters in a massive segmented active anticoincidence collimating shield. of CsI. The full energy range was divided into three sub-ranges, each with an optimized counter and collimator configuration. Walter was responsible for building the low energy counters and analyzing their data. HEAOA-1 was launched in Aug 1977 and produced many results on the spectra and time variations of Galactic and Extragalactic X-ray sources. One of the most important results was a catalog of hard X-Ray sources which was the only catalog of these sources for over twenty years.

Zierler:

Well, I want to ask you, Larry- I want to ask one last question for our talk. And that is, if you can reflect over your long career in X-ray astronomy, what are some of the most important things that you have learned?

Peterson:

First, I feel privileged to have been raised in a home where learning and curiosity were valued. I developed a hands-on interest in mechanical things and technology at a rather early age and obtained some proficiency in these areas. That helped find jobs to finance my way through college and later as an experimental physicist. I was also fortunate to start my scientific career at the dawn of the Space Age and to have been associated with some of the early, leading scientists in these areas. The faculty position I obtained at UCSD gave me the means to follow my own research interests. My group and I worked hard and were gratified to make early discoveries in the then-opening field of High Energy Space Astronomy. I feel very fortunate to have been able to assemble a group of research scientists, post docs and technical staff to implement experiments in X-Ray and Gamma Ray astronomy for balloon flights and spacecraft missions. This was a very cohesive group who both worked and socialized together. Our research also attracted very good quality Graduate Students. It is one of my satisfactions that many of my 18 + Graduate Students chose to continue working in the field and some became leaders in that field. All the members of the group were invested in the research and took pride in the results. I got pleasure from this that I regard as an accomplishment.

Zierler:

Well, Larry, I want to thank you for spending this time with me. It has been tremendous to hear all of your memories from your long and significant career. So, thank you so much for doing this.