Clyde Zaidins (PhD '67), Nuclear Astrophysicist and Science Communicator

Until you can verify it experimentally, even the most obvious-sounding ideas in science remaining exactly that: ideas. In the discussion below, Clyde Zaidins recounts his time as a graduate student at Caltech's Kellogg during its halcyon years when Willie Fowler was director, and when accelerator experiments demonstrated conclusively that stars are sites of massive nuclear reactions. To demonstrate this conclusively, and somewhat counterintuitively, researchers in Kellogg did not look up into the night sky with telescope; instead, they headed to the subterranean facilities where accelerators simulated conditions in stars by bombarding elements into one another. To understand what is happening in stellar interiors is the starting point not only of modern nuclear astrophysics, but of much of astrophysics in general, and Zaidins explains with pride Caltech's foundational role in these developments.

Following the completion of his graduate research, Zaidins joined the faculty at the University of Colorado, where he played a formative role in the creation of the Denver campus, and where he helped to launch the Center for Astrophysics and Space Astronomy. This center, coupled with JILA, formed the Joint Institute for Laboratory Astrophysics, a partnership formed between the University of Colorado and the National Institute of Standards and Technology, helped to make the Denver-Boulder area a world leader in astrophysics. For Zaidins, technical discovery was immensely satisfying, but this did not complete the goals that were most important to him. Early in his career, Zaidins embraced his role as a communicator of physics concepts, both to his students and to the broader public, and his website Just Ask Clyde, is a font of physics insight and explanation, accessible to all.

DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Monday, December 11, 2023. I'm delighted to be here with Professor Clyde Zaidins. Clyde, it's great to be with you. Thank you so much for joining me today.

CLYDE ZAIDINS: I'm happy to be here.

ZIERLER: To start, would you please tell me your title and institutional affiliation?

ZAIDINS: Okay, my full name is Clyde Stewart Zaidins. I typically don't need to use the middle name because my first and last name are unusual. I am a Professor Emeritus of Physics at the University of Colorado at Denver.

ZIERLER: I saw in your CV you went emeritus, and then you got pulled back in about 10 or 11 years later. What were the circumstances of that?

ZAIDINS: Without going into too much detail, I did retire at age 65. My wife, and I, and our young son moved to Washington state on the Long Beach Peninsula in the town of Ocean Park. And in 2013, I was contacted by the acting chair of the physics department, who was a geographer. It turns out that for a period of five years, no one in the physics department was willing to be the department chair. The department was having some real problems, and they wanted to save the department. The geographer, who was also an associate dean, said, "Would you be willing to come back, un-retire, and become chair of the department?" And after I realized he wasn't kidding–I'll leave out a lot of the details, but basically, I did come back. I started in 2015. They had to go through some hurdles because normally, an emeritus professor is not going to be the chairman of a department. But I was there for five years. We hired a really good person, a much more age-appropriate person, to be the chair of the department, and I retired on January 1, 2020

ZIERLER: Perfect timing, just before COVID.

ZAIDINS: Yes. I was planning to travel, but it didn't happen that way. [Laugh]

Stars As Nuclear Reactors

ZIERLER: Tell me about some of your overall research interests in physics. What kinds of problems have you worked on in your career?

ZAIDINS: Well, when I was in graduate school, I was in Willie Fowler's Kellogg Lab. And I got very interested in the nuclear reactions that occur in stars. When I came to Colorado, there was a–in fact, I should probably say a little bit about how I came to Colorado in the first place. I got my PhD at Caltech in Willie Fowler's lab. Ward Whaling was my thesis advisor. I'd always been interested in teaching. In fact, at age 9, I decided I wanted to be a scientist. And by the time I was in high school, I realized the best way to do that, because I enjoyed explaining things to people, a college professor was the thing to do. When I came to Colorado, I had been trained, of course, in nuclear physics. And at that time, there was no nuclear astrophysics at Colorado. But after I'd been there about five or six years, we formed a group of four people who got very interested in nuclear reactions in stars. For a period of time, we were doing research on that. I'd say that of all the research I've done, a little bit in several other fields, that was the one I was most passionate about. When I came to Colorado, with a fresh PhD, because I wanted to teach, I did not take a postdoc.

Most of my class of 1967 PhD students from Kellogg Lab went into postdocs or industry. But I decided I really wanted to teach. And the University of Colorado was in Boulder, but they had aspirations to start campuses in Colorado Springs and Denver. They already had an extension program in these two cities, but what they wanted to do was to start a real physics department, and of course, other departments, but it was the physics department that hired three of us to start the real physics department in Denver in 1967. We were tasked with doing our research in Boulder and doing our teaching in Denver. And by 1973, we actually became the University of Colorado at Denver. Before that, we were named the Denver Center, which was the extension center. At that point, I was with UC Denver for the rest of my career.

ZIERLER: Have you emphasized teaching over research over your career? Have you tried to blend them? What has been your approach?

ZAIDINS: Well, I've tried to blend them. But when I was doing research at the Cyclotron in Boulder, I arranged my schedule so that I spent a couple days a week in Boulder, plus some weekends. My teaching schedule in Denver was fixed. There were days that I would take the bus down to Denver to teach at the Denver campus, and then do my research on other days in Boulder. We had a tradition of having a coffee break at 10 o'clock in the morning, and a whole bunch of people were standing around. And one of the younger faculty asked a question of people. "If you were to have to give up either your research or your teaching, which one would you give up?" All the Boulder faculty said they would give up their teaching. When I said I would give up my research, they looked at me strangely.

But that was one of the reasons why this offer–in fact, when I was job hunting in 1967, and thanks to being a Caltech graduate, and second, at that point, it was still pretty easy to get jobs if you were qualified, I had a number of offers. I had, like, seven job offers at the end. I was in the process, in March of 1967, of trying to decide which one of the offers I wanted to take. I had asked Colorado–it wasn't an application, but I inquired about a position at the University of Colorado in the fall of 1966, and they said, "We don't have any new openings," so I just sort of forgot about it. I was contacted by David Lind, who was, at that particular semester, teaching in Denver. The way they were doing things before they hired the three of us in 1967, they would have part-time people from industry teaching the classes at the extension center in Denver and one Boulder faculty member who went down from Boulder to sort of oversee things. Dave determined very quickly this was not a sustainable model.

He was the one who really lobbied to get permanent people in the department so we could have people who would oversee the library, and actually have a physical presence on the campus with office hours and that sort of thing. He pushed that, and he was able to convince the chairman of the Boulder Physics Department and the Dean of arts and sciences to hire people. I was contacted in March, saying, "Would you still be interested in Colorado? Here is the situation. We're going to hire people to go down to start the department in Denver, but do their research in Boulder. Would you be interested?" I said, "Yes." "Okay, we'll give you an invitation." I went, did my campus interview, gave my talk to the entire Boulder Physics Department, and I got hired. And I've been there ever since. That was the way in which things were done.

ZIERLER: For the research, has your work been more on the experimental-observational side?

ZAIDINS: Oh, yes.

ZIERLER: You're not a theorist.

ZAIDINS: I'm not a theorist, I'm an experimentalist.

ZIERLER: What kinds of experiments have you worked on?

ZAIDINS: Starting in graduate school, there was the Caltech tandem accelerator. I don't know if it's still in existence at what was Kellogg Laboratories. In fact, my PhD thesis was on the production of oxygen in highly evolved stars. The question was–and the crucial experiment had been done at Caltech a few years before I came–how carbon was formed in stars. Now, you have a core of a highly evolved star that has carbon and helium. In fact, the formation of helium was this unusual triple alpha reaction, where three helium-4s come together to create carbon. (The helium-4 nucleus is also called an alpha particle). Now, you've got an environment where you have both helium and carbon. Is there a way to make oxygen? And the answer is, we got oxygen, so obviously that did work.

Part of my thesis, in fact, a major goal of my thesis, was to determine the rate at which this environment, which was rich in helium and carbon, would form oxygen. My experiment at the tandem accelerator in Kellogg Laboratory was my PhD thesis. When I went to Colorado, I was an experimental physicist working on reactions from particle accelerators. The University of Colorado had a fairly new cyclotron, so I simply switched from the tandem accelerator that was at Caltech to the cyclotron at the University of Colorado. And I did a number of experiments–always in collaboration. In an experimental situation, it's not a one-person job. Theorist can be a one-person job, but experiments usually have a group of at least three or four people.

ZIERLER: Is astrophysics the best way to describe your work, what you work on?

ZAIDINS: Nuclear astrophysics.

ZIERLER: What does the nuclear denote? What's the specificity of nuclear for astrophysics?

ZAIDINS: Basically, the temperatures, pressures, and conditions in stars are conducive to nuclear reactions occurring. Not like on Earth, where you have a particle accelerator, where you accelerate some nucleus to a fairly high energy, bang it into another nucleus, and see what reactions occur. That's what we experimentalists do. The star does it automatically because it's got a very high-pressure, high-temperature, high-density situation. What we try to do is to get the nuclear parameters that are necessary for the theorists, who are modeling stars in computers. They need to know what the nuclear reaction rates in the star would be based on what we have measured in a terrestrial laboratory. Basically, what we do is, we provide information that the theorists can then use to say, "This is what's happening in the star."

Accelerators as Star Simulators

ZIERLER: Are these tabletop experiments? Do you use telescopes?

ZAIDINS: No. Typically, accelerators are either in large rooms for radiation protection, thick walls, or down in the basement somewhere. We never even have to look at a star. Which is sad because it's nice to look at the stars. But basically, we simply do experiments where we accelerate a particle to crash into a target and look at what happens when we do that. That's what a lot of–not all–nuclear physics experiment are. And of course, probably the vast majority of nuclear physics experiments aren't related to astrophysics. Ours are. Because what we're trying to do is to simulate the reactions that would occur in a star. The conditions are incredibly different. But if we measure the appropriate parameters, those parameters can then be used to calculate what happens if the right conditions are actually inside the stars.

ZIERLER: The accelerators you work with, are they on campus? Do you work at national labs?

ZAIDINS: In my case, they were on campus. The tandem accelerator was in the old Kellogg Laboratory. I know the campus has changed. I think they've replaced the old Kellogg Building with another building. I don't know if it's still called Kellogg or not. The two buildings that were connected were Sloan and Kellogg when I was there in the 1960s. Is that still the name of those two buildings?

ZIERLER: Yeah.

ZAIDINS: They are east of Bridge. The accelerators were in the basement of Kellogg. And then, when I was at the University of Colorado–University of Colorado in Boulder has an east campus. The main campus, the one that you see all the beautiful architecture if you ever look at a picture of what the Boulder campus looks like, it was idyllic. And then, there's the city, and it's probably about a mile, mile and a half, and then there's the east campus, where a whole bunch of research buildings are. The cyclotron at the university of Colorado was still part of campus, but they call it the east campus. And that was where the cyclotron was. The cyclotron was defunded. It was funded by the federal government, by the Department of Energy. But the 1981 budget shut down a whole bunch of university facilities. This was the first budget from the Reagan Administration. Their reasoning was, "Why spend money to put accelerators on college campuses when the people could go and work at the national laboratories?"

That was, I think, a very unwise decision because it was a very different environment. On a university campus, the graduate students have to repair the machines, they have to actually work with the machines. If you're at the national laboratories, you bring your experimental apparatus. The infrastructure is set up so that you don't actually do anything with the accelerator itself. You say, "I want a beam with these characteristics down this beam line." You put your experimental stuff there, you take your data, go home, and analyze it at home. It's a very different experimental situation than actually working on the accelerator itself. Because there are certain routine maintenances that you have to do on any accelerator, and the graduate students are an extremely important part of that. At least they were in the days when I was a graduate student. Unfortunately, they're robbed of that opportunity today.

ZIERLER: I'm just thinking locally in Colorado, has NIST or JILA ever been assets for you?

ZAIDINS: Oh, yes. JILA, for sure. NIST, yeah, I have friends there, and JILA is, of course, half NIST and half University of Colorado. Carl Hansen, who was a very prominent theoretical astrophysicist, Jerry Peterson, Norb Roughton, and myself formed a group of people who used the Colorado cyclotron, and started doing nuclear astrophysics measurements. We started publishing papers on the parameters that were needed for the theorists to do calculations. Since Carl Hansen was a theorist, it was really great to have him as part of the group. We did our experiments from approximately 1974 to 1981, when the cyclotron was shut down. At that point, there was no longer the equipment to be able to do the experiments. And I think of all the experimental work I did in my entire career, it was that group, working with these three other guys, that was both the most rewarding, and we formed a really great friendship. Unfortunately, Carl and Norb have passed away, so it's just Jerry and I now. But we formed a really tight-knit group. And of course, we had postdocs working with us, we had graduate students working with us, we had undergraduate students working with us. It was fun. [Laugh]

ZIERLER: On the teaching side, have you ever gotten involved in thinking about the pedagogy behind physics teaching? Are you involved in the American Association of Physics Teachers?

ZAIDINS: Yeah. I joined the AAPT very early. I'm a fairly traditional lecturer. I won awards. I was a good lecturer, I think. Because it was something I really wanted. I was very enthusiastic about it. That always rubs off on students. I didn't do anything innovative, but what I did do, which I guess is innovative, is, in 1995 and '96, when the internet sort of blossomed in people's attention–it was around for a while, but that was where it really began to take off. I started putting all my classwork, that normally I would've put on reserve in the campus library, online. And one of my students wrote a nice letter to the president of the university saying that this was really great because he liked to study at 3 AM, when the library was not open. But he could go to the website I had set up and look at the stuff that I put online. I felt really good about that. And then, eventually, my wife Monica, who was an IT person, convinced me to post what I wrote during my lectures–I didn't use the board, I used to use the old-fashioned transparency projectors.

But at that point, there were art pads. Her suggestion, which I took, was to get one of the art pads. Then, as you wrote stuff, it would be projected for the students. Save it, then put that online, too. I wasn't just putting my solutions to homework problems or the solutions to the tests, but I was also putting what the students who were actually in class had seen on the board. Those people could go back and look again, or people who didn't come to class could look at what I'd put up. That probably is the one thing I would consider innovative. Because this was very early, '95, '96. Online courses were just coming into vogue, which I don't like, myself. But putting your own class material available for students on the internet I thought was a good idea. And I did that through the rest of my teaching career.

ZIERLER: Let's go back and establish some personal history. Where did you grow up? How did you come to learn of Caltech?

ZAIDINS: About two years ago, Kip Thorne gave a talk on his history in gravitation and on why he came to Caltech. Did you ever watch that?

ZIERLER: Absolutely.

ZAIDINS: It turns out Kip and I are almost the same age. He's one year younger than me. In that talk, which I watched, the things he was talking about while he was growing up, the two things that were really important were One, Two, Three… Infinity, the book that George Gamow wrote and the 1955 Time Magazine article on Caltech. Kip and I exchange emails occasionally, so I said to Kip, "I really enjoyed your talk. My background is so close to yours, except that I didn't want to be a snow plow operator because we didn't really have snow plows in Cincinnati, Ohio, where I grew up." [Laugh] But One, Two, Three… Infinity by George Gamow and the 1955 Time Magazine article were very influential. That was the background that I wanted to put in.

Kip then shared with me that he had exchanged letters with George Gamow, when he told George Gamow how important One, Two, Three… Infinity was for him. I grew up in Cincinnati, Ohio. I'm an only child. I went to Walnut Hills High School in Cincinnati. Walnut Hills is unusual. In 1895, the city of Cincinnati decided that it was going to create a college preparatory high school, similar to some of the ones on the East Coast, like Boston Latin, and Stuyvesant, and Bronx School of Science, schools like that that are public schools that had actual admission requirements. Cincinnati decided it was going to do the same thing. In 1895, they created Walnut Hills High School. When I was a kid, every fifth grader in the city of Cincinnati had to take a test. And if you scored above a certain threshold on that test, you were invited to come to Walnut Hills. I did. It was a six-year high school. You started in seventh grade and went through the 12th grade. It was just an absolutely fantastic school. And they were very early into advanced placement. I graduated from high school 1957.

And I had advanced placement classes in chemistry and calculus. And we just had very good English. When I was admitted to Caltech, I got an advanced placement credit for my chemistry and my math. And because my SAT score was so high in English, I went into an advanced section in English, where we skipped Freshman English and went into third-year English. As a result of that, at the beginning of my junior year, I still could have majored in physics, chemistry, or biology. I owe that to my high school upbringing. And it was sort of interesting in the sense that I went immediately into Calculus 2.

That particular year, I guess it was really hard. The very first test they gave in Calculus 2, more than 50% of the students flunked. I got a high C, which was one of the higher grades. [Laugh] That gives you an idea of the fact that my high school had prepared me extremely well. It was very important that I had gone to such a good high school, that I happened to have read One, Two, Three… Infinity. I was in the fourth grade when I decided I wanted to be a scientist. I had an extremely good science teacher in fourth grade. At that point, I went, "This is really what I want to do with my life." Then, going to a good school like Walnut Hills prepared me very well for Caltech.

ZIERLER: How did you hear about Caltech? How did it get on your radar?

ZAIDINS: The 1955 Time Magazine article. Cincinnati's close enough to the East Coast, and this was a college prep high school, so, "Oh, you're going to go to Yale. You're going to go to Harvard. If you're sciences, you're going to go to MIT or maybe Cornell." But you look east. I was the first person from my high school to go to Caltech in over 30 years, I think. Because people didn't think about looking west. But that article just really convinced me that was what I wanted to do.

ZIERLER: What year did you arrive in Pasadena?

ZAIDINS: In the fall of 1957.

ZIERLER: What do you remember? What sticks out in your memory from your first time there on campus?

ZAIDINS: I was really ready for that. I was never homesick. It was kind of interesting. I had a nice family life. Probably spoiled only child. I got along very well with my parents. But I was ready to leave the nest and enjoy Pasadena. I do have to say one thing, smog was almost at its worst, I think, historically in the late 1950s. Arie Jan Haagen-Smit had just figured out what smog was. He was an organic chemistry professor at Caltech. Anyway, what didn't I like about living in Pasadena? Smog. That was it. I was there, and I was in Blacker House. The room I was in had a view of the north. And I remember waking up, it was probably late October, early November. Because we started in September in those days. They may still. Of course, I loved freshman camp. That was really fun. It was still being held up in the mountains by San Bernardino when I was a freshman.

But I loved freshman camp. In fact, I actually went to freshman camp all four years because I was chosen to be one of the upperclassmen to go in my sophomore, junior, and senior year. They're still doing freshman camp, only they're doing it on Catalina.

Anyway, I woke up this one morning in October, and I looked out the window, and there were mountains there. I had no clue that the San Gabriel Mountains were there because of the smog. Well, it happened to be a Santa Ana condition. [Laugh] The result was, there happened to be these mountains that I'd never seen before. I don't know why that sticks out in my memory, but it does. It was just that it was possible to not have smog if the wind was blowing just right.

ZIERLER: Was it physics from the beginning for you?

ZAIDINS: No. Like I said, at the beginning of my junior year, I could have majored in physics, biology, or chemistry. I just basically loved science, loved all of this. In fact, I did get a lot of As. I graduated with honors. But I never got an A+ in physics. I got one A+ in chemistry and one A+ in biology, but none in physics. [Laugh] I think what killed biology for me was biochemistry. It was such an enormous amount of memorization. I thought, "That's not really what I want to do with my life." I still loved chemistry, but I did decide that I liked physics better. At the beginning of my junior year, I made the choice that physics was what I was going to major in.

ZIERLER: As an undergraduate, who were some of the professors that stick out in your memory? Who were some really great teachers?

ZAIDINS: Jon Mathews. He was not famous for his research. He perished on a round-the-world sailboat trip. He and his wife were going around the world, and they disappeared in a storm in the Indian Ocean. He was the best lecturer. John D. Roberts of Chemistry comes to mind. Because I loved organic chemistry, which is weird because I just said I don't like memorizing things. But organic chemistry sort of did resonate with me. Bob Leighton was a very important faculty member for me. I had a couple of classes with Jon Mathews. He was so prepared and gave such good lectures. It was very clear.

I don't know how the student houses have changed, but when I first came there, it wasn't until, I think, my senior year that they added the three new houses.

When I came, there were only the four original houses. And we would invite faculty members to come to dinner, then sit around and talk with them. And Lee DuBridge came to dinner one time. Someone asked him, "Who was your best professor in college?" And he mentioned somebody who none of us had ever heard of. He said, "What was so good about him was that he made mistakes in his lecture. And then, you had to go home, and go through your notes, and figure out where the mistakes were. And you learned so much by doing that." I think we were all kind of impressed by Lee DuBridge's take on what made a good teacher because it wasn't what you would think. I had George Beadle for biology, also a great teacher. I won't mention the bad teachers, but I had a couple. This is Caltech, but I had two terrible teachers that just stick out in my memory. [Laugh]

The Giants of Caltech Physics

ZIERLER: What made it physics for you following junior year? How did you focus on physics?

ZAIDINS: Just basically taking the courses. I didn't know what I wanted to do in terms of a PhD thesis. I knew I had to do a thesis. In fact, it was kind of interesting, Robert Bacher was my undergraduate advisor. When I went into my senior year–and I really didn't know what field, I just knew I wanted to get a PhD so I could be a college professor. It wasn't that I was passionate about some particular area of physics. I just liked physics, all of it. I asked Professor Bacher, "I want to go to graduate school. I want to be a professor. And I'm looking at a couple of places." He said, "Why don't you stay here?" "Okay." [Laugh] That's why I became a lifer. I don't know if you hear that term anymore.

ZIERLER: There aren't many.

ZAIDINS: Robert Leighton is a real lifer because he not only did his undergraduate and graduate, but he stayed on as a professor. But he was very good. And I liked Ward Whaling, and it turned out I chose him to be my thesis advisor. I went into graduate school, and I'm still taking courses, and I have to make a decision about where I'm going to do my research to do my thesis. And Ward Whaling was teaching nuclear that year. Usually, Willie Fowler taught it, but Willie was on sabbatical that year. I really liked the nuclear physics course. It was my favorite course of my first year in graduate school. I went to Ward Whaling and said, "I'd like to join Kellogg as a graduate student." He said, "Fine. I've got a project for you." This was the summer after my first year. It was a research project in terms of going to the library.

By that time I'd already realized I wasn't smart enough to be a theorist. I was smart enough to be an experimentalist but not a theorist. That was why I chose an experimental path. I did this project, and it turned into a publication. You accelerate a beam of particles in an accelerator, and you pass it through a very thin foil so the particles don't lose very much energy. But they enter the foil with just one charge because that's what the accelerator produces. But after they pass through the foil, they will have a combination of charges. Turned out that in my thesis, I was accelerating carbon. Carbon, charge one, hits the foil. It comes out, some of it's charge one, some of it's charge two, some of it's charge three, can go all the way up to charge six. What percentage of the beam after it passes through this foil is going to be in each of those charge states? And that was something in 1961, which was my first year in graduate school–people had been doing the experiments, but there was a lot of missing data.

The project that Ward Whaling sent me on was to try to do some sort of systematic search so that people could know what to expect for particles passing through a thin foil. Before we were actually able to start our experimental work, we had to take the shop course, and I happened to grow up in a situation where I didn't do manual projects–a lot of people tinker, work on their cars, stuff like that. I'm an experimentalist, but I didn't have any of that background in the environment where I grew up. I had to kind of pick that up as I went along. I had to take the shop course, and I was helping other graduate students with their research. Because basically, at least in those days, when you're doing any kind of nuclear physics experiment, the machines are running 24 hours a day to make full use of what you've got. You need somebody to work the midnight to 8 am shift. Anyway, it wasn't until later that I got the opportunity to start working on my own project.

ZIERLER: How much opportunity did you have to interact with Willie Fowler?

ZAIDINS: A lot. Willie Fowler wasn't my thesis advisor. The truth is, he was every graduate student at Kellogg's thesis advisor unofficially. Because he was very, very involved in what everybody was doing. He was an amazing person. He really was.

ZIERLER: What was he like?

ZAIDINS: Very fun. Once you're a graduate student in Kellogg, you're a graduate student for life. I invited him to give a series of talks in Colorado. This was just before he won his Nobel Prize in 1983. When he won his Nobel Prize, everybody was calling me and saying, "We met this guy, and he gave a bunch of talks, and we loved it. Now, he's a Nobel Prize winner." [Laugh] Plus, when he gave his first press conference after winning his Nobel Prize, he said, "Everybody who's ever worked with me deserves part of this prize." I can claim I have some fraction of a Nobel Prize. Anyway, one of my colleagues, another professor, would tease me.

After the talks, we were sitting around. Willie was a great beer drinker. We were talking. "Zaidins, get me another beer." [Laugh] I got teased about that a lot. Like I said, graduate student for life. He was very bright. One of the very first things that I did when I was helping somebody else with their experiment, I don't remember the details, I do remember the outcome. We had a very thin detector, just at the very early stages of semiconductor particle detectors. And it turned out that this particular detector was not supposed to be either heated up or cooled down too quickly. It had to be done slowly.

And I didn't know that. The result was, I broke the detector. I don't remember how much it cost, but it was a lot. I was told I had to go and see Willie about it because we were reasonably well-funded, but we certainly couldn't afford everything. He told me about when he was a student at Ohio State in the 1930s, he was doing experiments on sound, and they had a very thin vibrating membrane for detecting sound. And he broke it. He made me feel really at ease because he had had a similar experiment breaking a valuable piece of equipment when he was doing research at Ohio State. Anyway, he was a cool guy all the way around.

Bombarding Oxygen with Carbon

ZIERLER: What was the state of nuclear astrophysics at that point? What was the frontier of knowledge? What were the big questions to be pursued?

ZAIDINS: A lot of them had already been answered. There's a famous paper, 1957's Burbidge, Burbidge, Fowler, and Hoyle, referred to as B2FH. Margaret Burbidge died a couple years ago at age 100. But these four people, the three British people and Willie, came up with pretty much the story–with a lot of details still needed to be filled in, so basically, we were just filling in details, to a large extent. Where the reactions occurred, that was still stuff being done. But the framework for nuclear astrophysics was pretty much set by B2FH. And by Al Cameron. He was working by himself in Canada and came up with pretty much the same thing. He was sort of underappreciated, in a sense.

I'm glad that Willie won the Nobel Prize, but there could be arguments made that maybe other people should've been included on that besides Willie. But Willie basically got the Prize for everybody working in that field. And one of the unanswered questions when I was assigned my thesis–and I didn't come up with the idea, I was told, "This is an open question. Would you be willing to work on it?" And I said, "Yes." What is the reaction rate for forming oxygen in this environment that I mentioned before with helium and carbon? Basically, I needed to measure the rate–I could do experiments in the laboratory, which could then be used to–one way of looking at an oxygen nucleus, and there are many, many ways to look at it, is that it is already a cluster of a carbon and an alpha particle put together. What fraction of the description of an oxygen ground state can be looked at in this way of an already existing carbon and helium nucleus? It turned out the answer I got was about 10%.

If you were going to say, "How do you describe the oxygen ground state?" you could say, "10% of the time, it kind of looks like a carbon-12 and a helium-4 nucleus." And that number is very important in what the reaction rate is when you actually bring an alpha particle and a carbon together. My goal was to make that measurement. And the first set of measurements we made with a couple of postdocs, one from Switzerland and one from Israel, we came up with a bunch of measurements. It turned out those measurements, although there was nothing wrong with them, could not give us the number that we needed. I had to start all over again in 1964. From '61 to the spring of '64, I was working on one set of experiments that turned out to be a blind alley. This happens in research. It was very fortuitous that I had an opportunity to take the summer off. They were organizing, at Princeton University, a summer course for those people who taught physics in the HBCUs. They weren't called HBCUs then, but historically Black colleges and universities.

They were going to introduce to the faculty members who taught at these institutions the new PSSC. That was a method for teaching physics that was developed at MIT. Basically, they had invited–and I recall there was something like 40 to 50 people who were teaching at the HBCUs. Aaron Lemonick, who was a professor at Princeton, was in charge, but they needed four teaching assistants for the laboratories, and to answer questions, and so on. They wanted geographic distribution, so they called Caltech and said, "Do you have a TA who would be willing to come that you'd recommend?" And they recommended me. I spent the summer there, and that was good because I had just spent a couple of years working on an experiment that was not going to give me what I needed for my thesis. When I came back in the fall, I was refreshed. It was a very interesting summer.

ZIERLER: How did your research take a turn as a result?

ZAIDINS: Actually, Willie Fowler and Ward Whaling suggested a different technique to make the same measurement, which was bombarding a lithium target with a carbon beam. I just said that oxygen-16 looks like 10% an alpha particle and a carbon-12. Lithium-6 is a much higher percentage, almost 100%, an alpha particle and a deuteron, a deuterium nucleus. Basically, the carbon comes in, captures the helium particle from the lithium-6, and leaves the deuterium alone. Of course, they're all moving. And you detect the deuterium particles. From that, you can tell what happened in the interaction. That was an indirect way of measuring the number that we needed because what you were basically doing was taking the helium from the lithium-6, sticking it to the carbon, and using the deuterium to tell us what happened.

That was the actual way that I finished my thesis. It was a whole new way to do it. And the original experiment that didn't work out was bombarding oxygen with carbon. There was a theorist who said that would give us what we needed, but once he saw the data, he said, "No, there's no way we can get what we need from it." That was the spring of '64. And then, I got this opportunity to do something different for the summer. Of course, teaching was always one of my first loves, so it was really fun to–that was an extremely important summer in my life. First of all, being introduced to all the people who taught at these colleges, mostly in the South.

ZIERLER: What were the conclusions of your research? What did you find?

ZAIDINS: Probably the simplest explanation was, once all the helium is gone, there are no more reactions of that type. Basically, the star has to do something else. It can no longer keep itself going by getting the energy out of helium interacting with itself to make carbon and interacting with carbon to make oxygen. At some point, the helium's all gone. How much carbon and how much oxygen? The answer was about 50/50. Without going into how you get to that answer, that was the final basic result. The two results were, yes, oxygen-16 ground state does look 10% of the time like carbon-12 plus helium-4. And if you put this into a red giant star that's burning helium, it's going to give you about 50% carbon, 50% oxygen when all the helium's gone.

ZIERLER: How did that connect with bigger questions in physics at the time? Particle physics, nuclear physics, astrophysics.

ZAIDINS: Pretty much, it's its own thing. How do you make oxygen? The real question, starting, say, after the Burbidge, Burbidge, Fowler, and Hoyle paper, was, "Okay, we think we can make carbon, we think we can make oxygen. How do we do it, and what will be the results?" Because we live in a world where carbon and oxygen are extremely important. If we want to have life, we've got to have carbon, we've got to have oxygen. Basically, we think they're made in stars. Can we somehow show that they're made in stars? And the research I did on oxygen said, "Yes, we can, and we can make it in reasonable quantities." It basically answered the question, "Do stars make carbon and oxygen?" And my part of that was, "Yes, they make oxygen. And they make it in sufficient quantities that we're here, we have something to breathe. We have water. You don't have water without oxygen."

ZIERLER: You've indicated Caltech was obviously a research leader in this area. Was there anyone else that was in competition with Fowler's group? Was this really only happening in the Kellogg Lab as far as you knew?

ZAIDINS: In the late 50s, early 60s, they were pretty much the forefront. Today, they don't do it at all. There are places like Notre Dame, Ohio State University, places like that. There are other places. I'm not keeping up on that these days. But basically, it shifted to other places. What we're doing is filling in finer and finer details. There's not expected to be any amazing breakthroughs. We're going to add decimal points to numbers and things like that.

ZIERLER: You mentioned Fowler's collaboration with the Burbidges and Fred Hoyle. Did you ever engage with Willie on his feelings about the Big Bang versus the so-called steady state theory?

ZAIDINS: No, not really. 1964 was the year that Penzias and Wilson found the cosmic microwave background. Since then almost everyone favors the Big Bang. Fred Hoyle was a very interesting person. I barely interacted with him, but he did spend summers at Caltech frequently. He always was the contrarian. He always had different ways. He never accepted the Big Bang. Even though he named it, he didn't accept it.

ZIERLER: Well, didn't he name it the Big Bang sort of derisively?

ZAIDINS: Yes, exactly. He was in some BBC interview. The original person was Father Georges Lemaitre. And it's sort of interesting because I was consulting with Willie Fowler when I was getting ready for my first real sabbatical, and I had an opportunity to do something in the United States and an opportunity to work in France. And Willie said, "Take the one overseas. It changed my life." He had his first sabbatical at Cambridge. And he got a chance to meet Georges Lemaitre. He's the person who actually–it wasn't called the Big Bang, but he was the person who took Einstein's equations and showed that a very persuasive solution–it wasn't the only solution but a very persuasive solution–to Einstein's equations just after General Relativity came out. It was that the universe started in a very small volume and expanded. And at that point, more and more evidence was showing the universe was expanding. Willie was telling me about this opportunity to be sitting in a room with Father Lemaitre and several other physicists and hearing him talk about his work in the early part of the 20th century. Willie shared his emotions wonderfully. He was fantastic. He was not stuffy at all, he was a real person. And very bright.

The Dynamism of Richard Feynman

ZIERLER: Did you ever interact with Feynman?

ZAIDINS: Oh, yes.

ZIERLER: Did Feynman ever come around the Kellogg Lab?

ZAIDINS: Not around the Kellogg Lab. When the three volume Feynman Lectures were given, I was a TA at that time working with James Hartle, who's now a professor emeritus at University of California, Santa Barbara…

ZIERLER: Unfortunately, he's passed.

ZAIDINS: Oh, no. I hadn't heard. He and I were really good friends. But obviously, we've lost contact. When did he pass?

ZIERLER: Recently. I think last year.

ZAIDINS: It's been a couple years since I'd interacted with him. But he and I were the people who were recording the lectures. In fact, they're now on the web. You can actually go and hear the original tapes. One time, and I think it was October of '61–it was the old reel-to-reel recorders. We'd wind it, and then we'd talk to make sure that it went pretty far into the tape before we started recording his lectures. I would do that, like, half an hour, 20 minutes before the lights went on and the students came in. I was in front with a Lavalier mic recording, "Today is October 16, 1961. Professor Feynman's lecture today is on blah, blah, blah." Feynman came in and tickled me. You can actually go to that tape and hear me laughing because Feynman tickled me. [Laugh] This is a true story, and the evidence is there. I've been telling this story for years because it's kind of a typical Feynman thing to do. Now that these tapes are actually on the internet, you can hear me with that particular spiel, trying to avoid laughing while recording that message.

ZIERLER: What was he like in the classroom? What was his style like as a lecturer?

ZAIDINS: Oh, fantastic. He was so dynamic. He had this one demonstration where people held their breath. The conservation of energy. He had a bowling ball on a rope, and then it went out and came back to within millimeters of his nose. Everybody in the audience was holding their breath. I remember that one in particular. But I do recall one thing. When he was talking about optics and the fact that people could cross their eyes. Because when you're looking at a distance, your eyes are parallel under normal conditions. And then, if you have to focus really closely, your eyes automatically go in. That's how a lot of people are able to cross their eyes. But Feynman said because there's no reason to make your eyes go out, people can't do that. At the end of the lecture, a student came up to Feynman, looked at him, and his eyes went out just like that. [Laugh] Anyway, Feynman was completely wrong.

ZIERLER: You mentioned already that you weren't thinking about a postdoc because you really did want to focus on teaching. Was that already the norm for people interested in research? Was going on to the postdoc sort of the standard thing to do, even back then?

ZAIDINS: Yes. Absolutely. There were nine of us who got our PhDs in Kellogg in '67. It was an unusually large class. There was actually a guy, Dave Goosman, who was only there four years, and Larson, I can't remember his first name, who'd been there 10 years. It took me six years. All of a sudden, all of us got our PhDs at one time. I think I was the only one who went into a teaching position. But it was this unusual teaching situation, this real challenge of, "Okay, you're going to be teaching classes to basically older students." My very first class at the University of Colorado at Denver, I was 28 years old, and I was younger than the median of the students that I had in my class. It was an evening class, it was a group of people who were going back to school, who had families, who had jobs, and so on.

It was the middle of the Vietnam War. Most of the jobs that I had offers on were–I had three offers from the California State University system. Cal State LA, Cal State Long Beach, Cal State San Diego, which were basically teaching, no research at all. Which I was willing to do because like I said, teaching was my main focus more than the research, but I liked the idea of some of the places, University of Idaho, University of Pittsburgh. Those were the main ones. There were a couple of others I can't remember. But when this opportunity came on pretty late in the season, it was March of '67, "Gosh, that's really great. I'm going to be teaching older students, I'm going to still have an opportunity to do some interesting research, Colorado's a beautiful state. Okay. If I get the offer from there, then that's what I'll choose." And I did.

ZIERLER: Right from the beginning, there was already this duality of being between Boulder and Denver?

ZAIDINS: Yes. Because in those days, we were in an old streetcar barn. The campus wasn't really built until the 1970s. We were in downtown buildings. We were in repurposed buildings spread out over downtown Denver. It was a very interesting time. I've been blessed in the sense that I've had an interesting life and was in on the ground floor. And I'm one of the last people left. That was over 55 years ago that I came there. And then, coming back–I was 81 years old when I retired in 2020. I thought I had retired at 65. [Laugh]

ZIERLER: Where was your main office?

ZAIDINS: I had offices. At one point, I had three offices. I had an office on the main campus in Boulder. I shared it with another faculty person because I wasn't there very often. But I went to colloquia and so on. Because the three of us that were hired, John Shonle, Robert Rogers, and myself–John and Bob Rogers were more senior. They were hired at the associate professor level with tenure. I, of course, came in as an assistant professor without tenure because the ink wasn't even dry on my PhD thesis when I got my degree and was hired. I had an office on the main campus in Boulder, I had an office where the cyclotron building was, and then I had an office in Denver, so I had all three. If I had to choose what was my main office, it was probably the one at the cyclotron. Because I went to the main campus for colloquia, a couple of colloquia and seminars a week, but I spent most of my Boulder time at the cyclotron. And I had to share an office in Denver. Since we were in buildings all over downtown, we didn't have a lot of extra space.

ZIERLER: This formative collaboration that you mentioned, how did it get started when you became a professor?

ZAIDINS: Oh, I walked into the cyclotron. "Here are things we would like you to work on." [Laugh] And of course, in those days, there was no nuclear astrophysics there. It wasn't until the early 1970s that Norb Roughton, who was a professor at Regis University, the Jesuit school in Denver, who had gotten his PhD in nuclear astrophysics at Washington University in St. Louis–Jerry Peterson was a new assistant professor. He and I were both assistant professors at that time. I was just about to be promoted to associate professor. And Carl Hansen, who was the theorist at JILA. The group of us got together and said, "We can do interesting things. And it's going to be in nuclear astrophysics."

Because between '67, when I started working on certain nuclear reactions–and they were interesting. Nuclear physics is fun. But they weren't nuclear astrophysics related, they were just nuclear physics related. We said, "Here are a bunch of things that we can do to measure reaction rates in advanced stages of stars. And we can do it by a technique, which is very unusual." It was thick targets. Typically, when you do nuclear physics, at least low-energy nuclear physics, you get as thin a target as you can, and then the beam passes through, and the reactions occur in that thin target. We figured out a way to irradiate thick targets and then measure the residual radioactivity that was created in the thick targets. I have to tell you a story about Willie Fowler. In I think 1974, plus or minus a year or two, we had started publishing this thick target work. And people were raising their eyebrows.

Willie said, "There are a lot of people who think this is all BS. We'll invite you to come and give a talk to defend yourself." I said, "I'm perfectly willing to do that." I came to Caltech to give a talk. Kellogg had Friday evening colloquia, and then we'd always have a party afterwards. I came there, and one of the people who was at Kellogg at that time had been a postdoc at Colorado, so I knew him. He said, "You're walking into an ambush. I hope you realize that." [Laugh] Anyway, I gave my talk. I've given a lot of talks in my life, but this was one of the very few times that I didn't finish what I planned to say because I kept getting question, after question, after question. One of the things Willie did, Willie raised his hand and stood up. "Zaidins, you've set nuclear astrophysics back forty years. [Laugh] We did thick targets in the 1940s, and it wasn't any good. Why are you doing this?" And then, Eric Adelberger, who's a very animated guy, gets up and says, "Okay, Clyde, why don't you return to the ways of your forefathers?" [Laugh] I did a reasonable job, I thought, of protecting myself, but the warning that I'd walked into an ambush was true. Afterwards, there was going to be a party at Charlie Barnes's house.

Ardie Fowler was Willy's first wife. That family has a very interesting history. Olmsted, I think, was Ardie's maiden name. They were one of the pioneer families in Pasadena, and Willie wound up marrying into the Olmsted clan. Anyway, Ardie wasn't doing very well at that point. She passed away a few years later. Kellogg was a family, everyone knew each other, so Willy and I went over to Willie's house before the party to see Ardie. Willie drove me because I was from out of town, no car or anything. He took me, and we chatted with Ardie for a little bit because she wasn't going to be well enough to go to the party, but she wanted to see me. We had a little conversation. Then Willy and I walk into the party a little bit late because we'd stopped off to see Ardie, and Willie and I are arm-in-arm coming in after what looked like a big fight at the actual colloquium itself.

Tom Tombrello, who was an interesting influence, a fresh assistant professor when I was a graduate student, he always was able to get to the really key things. He said, "Here is the question we have. Is it possible to properly treat resonances in the thick target? If you can show that that is the situation, then I'm convinced."

And if Tombrello is convinced, everybody else is going to be convinced. I think Tombrello was probably the smartest person in the room most of the time. He passed away also. Basically, I went back to Colorado, quickly wrote a paper that I thought answered Tombrello's question, got it published, and the controversy was over. Suddenly, Colorado's data was no longer suspect. It's good data. That was what happened.

In 1967 Tombrello was on my thesis defense. And obviously, I passed because I got my degree and had a career. But Tombrello said, "This carbon on lithium is not carbon on helium." Tombrello said, "You did good work. I just don't believe your result because the whole technique is so indirect." He was very candid about it. "I personally don't know whether I can trust the result." Kind of a downer.

I did get my PhD. About three, maybe four years later, I was at a conference somewhere else, and Tombrello came up to me. He put his arm around me. He said, "Steve Koonin and I theoretically calculated the reduced alpha width," which is the parameter I'm talking about, "and we got the same results you did. I trust your answer now." That was really a, "Yes," moment. [Laugh] I am so happy that I have had the opportunity to be around so many brilliant people in my life. It's been wonderful to be able to interact with people like Feynman, and Tombrello, and Fowler, and so on. It's been exciting.

The Origins of UC Denver

ZIERLER: Administratively, were you part of the creation of the University of Colorado at Denver as its own independent campus?

ZAIDINS: Oh, yeah. Absolutely. The whole creation of that campus was not easy. Internal politics in the state. For example, Boulder was pretty much Boulder-centric, and the regents and the administration, Boulder was it. "We've got these operations in Colorado Springs and Denver, but Boulder's the big deal." The state legislature was always pushing the University of Colorado to do something more for other parts of the state because the population centers of Colorado Springs and Denver were bigger than Boulder. The regents and administration were dragging their feet in the early 1960s, so the state legislature said, "Okay, we're tired of this. We're going to create Metropolitan State University, and that's going to be the big thing in Denver." "Oh, no, no, we don't want that. We get the message, we'll start doing things."

There's this tremendous competition now between University of Colorado trying to expand its operations–Colorado Springs, I think, was going to be a foregone conclusion. But Denver, we now have a major competition between CU Denver and Metropolitan State University, which the state legislature was favoring. There were times during the first 10 years that I was there that there was a risk of us actually being put out of business. It was kind of a rough time. It turned out it all worked out. The University of Colorado said, "Okay, we want to create the University of Colorado at Denver and University of Colorado at Colorado Springs. We're no longer going to have these as extension centers." And the state attorney general said, "Uh-uh. The constitution of the state of Colorado says the University of Colorado is in Boulder. If you want to create Colorado Springs and Denver campuses, you have to get a constitutional amendment."

In 1972, during the general elections, there was a statewide constitutional amendment vote to make it possible for the University of Colorado to create campuses that were called University of Colorado at wherever, and that passed 51% to 49%. In 1973, we officially became the University of Colorado at Denver. I was pretty active politically in the university system. I didn't play what you would call a leading role, but I was part of a group of people who were trying to get us to be a legitimate campus. We did a few things. One of the things I'm proud of, even though in the long run, it didn't work out, a chemistry professor and I (Robert Damrauer) created what were called Topics in Science modules. Students, for their general education, have to take a certain amount in various fields.

We decided instead of them taking a year-long course in introductory physics or introductory chemistry, which is usually a watered-down version of what we give the majors, "Why don't we take a topic like nuclear reactions in stars, teach it for five weeks, and the students can pick and choose these modules, then put a group of modules together so they'll have something that is an interesting topic, not just preparing you for further courses you're not going to take?" We actually got a National Science Foundation grant, this chemistry professor and I did, and we created this set of courses. It was going very well. And then, the curriculum people said, "Okay, we're not going to allow these anymore. We're going to require people to go back to the old system," so we stopped teaching those courses. But it was something I'm very proud of because it was very good during the time it was in existence, and the National Science Foundation thought it was a good idea, too. They gave us money to continue to develop it.

ZIERLER: This was the CAUSE grant you're referring to?

ZAIDINS: Yeah.

ZIERLER: What came as a result of this?

ZAIDINS: We created a bunch of modules that were going to be taught eventually. It was a good idea, and we got people involved that weren't involved otherwise. We were teaching these modules as an overload. We have to teach our majors, we have to teach our introductory courses. For a 15-week semester, we would teach our usual two courses, and then for five weeks during that period, we would teach a module. For five weeks during a 15-week semester, we would have an overload. And sometimes, we would team-teach courses. I have a really good friend, Linda Dixon, who's a geneticist. Linda and I taught a module, Radiation and Life. I would teach the physics part of the radiation, and she would teach the effect of radiation on living material and so on. We taught that several times. Anyway, we got people interested from a much wider range. Because normally, people don't want to teach an overload. And even at CU Denver, not everybody has teaching as their primary love. I told you about the Boulder people liked their research, but some of them are still very good teachers. But I would say with no data, just attitudes and interacting with people, that a much higher percentage of the people in Denver think teaching is more important than research as opposed to Boulder, where I think it's probably fair to say the majority of people would say research is more important than teaching.

ZIERLER: In the 1980s, tell me about some of the sabbaticals you were able to take in Europe and how that was valuable for you.

ZAIDINS: Oh, fantastic. In terms of professional, marginal. It was interesting. But it changed my whole view of the world. It was great. My first sabbatical was all at the University of Paris South Campus. In the French system, the major research for general science, not classified work, because the French also have classified research, but CNRS is their main national science foundation thing. Basically, if you become part of the group of CNRS, and this is all research-related, these people do not have to teach if they don't want to, you get a position for life. I imagine that it's just like with tenure. If you really screw up, you can be fired. But these people are given this opportunity, a salary. They're not guaranteed to have a place to work, but they are guaranteed that they're a researcher with CNRS.

The town is Orsay south of Paris. It's about a 45-minute train ride into Paris from Orsay. And that was where I was located. After World War II, the Curie's Lab in Paris in the main part of the city was just too small a space in a highly urbanized area, so they needed to move. In this area around Orsay was a very wealthy collaborationist during World War II, so the government seized his land and built a research center in Orsay. And part of that research center was devoted to this nuclear physics laboratory and to the University of Paris's south campus. That was where my office was, that was where I worked. And I met some really interesting people. Not my immediate supervisor, but the head of the laboratory was Marie Curie's granddaughter, Madam Hélène Langevin-Joliot. It was really neat to be invited to their house for dinner and to see the actual Nobel medals from her grandmother and her parents. It was really interesting to actually be involved with the Curie family.

I enjoyed the research I did there. I don't think it was groundbreaking. We did do some interesting work. We had two weeks at the–this was before the Large Hadron Collider in Geneva–at CERN. I had two weeks at CERN, which was a fun thing to do. That sabbatical was very interesting, and I arrived naively, as a lot of times I do, living in France without speaking any French. [Laugh] I arrived there having never taken any French. My work was pretty much almost all in English. In fact, people would come to me, French people who had written a paper in English, but they wanted it to sound much more like a person who had English as a native language. I had a postdoc from Japan who asked me to look at his paper he'd written in English, and then a French person the same day had two papers in front of me. I did a lot of this. I remember one of the French people said, "Make it not sound so heavy."

In French, every word has articles. You basically never use a noun without having the article in front of it. And part of the reason is that it tells you whether a word is masculine or feminine. One of the great things about the English language, which isn't an easy language, is we don't have to deal with gender in our language, unless they actually refer to people or animals. In French, a fork is either masculine or feminine, a spoon is either masculine or feminine. Anyway, there are all these extra articles, and you have to sort of strike them out, the's and a's and an's where you would not normally expect them. Whereas there are no articles in Asian languages. The Japanese will write things where you should have some articles, and they aren't there. I had this fantasy of somehow scraping all the extra articles off the French paper and having them land in the paper written by the Japanese fellow. [Laugh]

Astrophysics Leadership in Colorado

ZIERLER: Back at Colorado, tell me about the Center for Astrophysics and Space Astronomy and your affiliation there.

ZAIDINS: When the cyclotron was shut down, I still wanted to be doing research. I was a full professor at that time. I don't want to make it sound like I hate research. But this was kind of an interesting thing because they were doing extreme ultraviolet astronomy, and they needed somebody–most of their people were either astronomers or astrophysicists who had not had a strong grounding in experimental physics itself. Some of the questions they had when they were designing their apparatus were ones that I could help with. They basically recruited me. Because I was looking for something to do when the cyclotron was shut. I was still living in Boulder at that time. I would commute to Denver.

I've been living in Denver since 1989, but between 1967 and '89, I lived in Boulder. Basically, the CASA group were flying experiments on rocket launches from White Sands. Their instruments were looking at the extreme ultraviolet, EUV, part of the ultraviolet spectrum that's right next to X-rays. It's much shorter wavelengths, much higher energy than the standard UV that we get from sunlight, but not quite high enough to be considered X-rays. This is something that's absorbed very quickly in the upper atmosphere, so if you want to look at astronomical objects that emit extreme ultraviolet, you've got to get up above the atmosphere. And there were a whole bunch of leftover rockets at White Sands.

I'm sure CASA wasn't the only group that was using White Sands to launch experimental–you have, like, five minutes above the atmosphere, so you can get a bunch of measurements of extreme ultraviolet spectra and then hopefully recover your instruments. But you've also got telemetry, so in case something happens, if your instruments are destroyed, you at least have the data that was taken because you collected it with telemetry. Basically, I only went down to White Sands once, but I worked on the kind of detectors that detect extreme ultraviolet, and calculated how they worked, and so on. I was involved in instrument design.

ZIERLER: Tell me about some of the students who are interested in physics at CU Denver. What kind of careers do they go on to?

ZAIDINS: Our very first graduate–when we first went there, we were only teaching the very basic introduction courses, so it took a few years and adding a few extra people to the faculty before we started to be able to give closer to a real physics major. Our very first physics major, a fellow by the name of Leon Whitney, and this was when Hyman Rickover was still in charge of the nuclear Navy. In those days, just like Jimmy Carter, anybody who wanted to work in the nuclear Navy had to be interviewed by Admiral Rickover himself. Leon Whitney was our first graduate, worked many years in the Navy, and then after he got out of the Navy, he a nuclear safety inspector around the country. That was his post-Navy job. He's retired now.

He got his degree in the early 1970s, so he's not a young man anymore. But he was the first one. We've had some really super graduates. Carol Johnson is at NIST. I don't know if she's still there, but she was there when I visited the East Coast a few years ago. She was one of the best students that I ever had. She got her PhD at Harvard, but she did her undergraduate work at CU Denver. James Mason was a student, also brilliant. He came to Caltech, so he's a Caltech PhD. He was working with Robbie Vogt on some of the aspects of LIGO. He's now with Lockheed Martin, or he was last time I interacted with him.

Karen Jonscher (Caltech PhD) has a position as a physicist at the University of Colorado Medical School. Robert Topel has his own company in Portland, Oregon. He comes and visits from time to time. I know I'm leaving out some–every few years, we have some super good students, and they're typically never traditional students. The traditional student right out of high school is going to go to Boulder if they're going to go to the University of Colorado. Colorado State University in Fort Collins is a very good school, too. We tend to get those people who come back to school after they've done something else in their lives.

ZIERLER: Have you appreciated that as a professor, interacting with students who have a bit more life experience?

ZAIDINS: Oh, absolutely. When I was invited in the spring of '67 to visit, I came down in the evening when the evening classes were being held. "Man, this is exactly something that I think is really worthwhile." It wasn't that I didn't want to teach the typical student. I was a TA for six years at graduate school in Caltech, and I certainly enjoyed the sections in physics. I would imagine things are still organized the way they once were, where you have lectures, and then when it comes to actual problem-solving and so on, they break off and go into rooms of about 20 apiece. That was what we did as TAs when I was a TA during the 60s. I had my teaching experience.

Plus, that was the reason why I was able to go to Princeton in the summer of '64 because I'd had already teaching experience as a teaching assistant there. I had one year where I had a United States Steel Foundation Fellowship, and I was going to be able to just work on my thesis and not teach. And by that time, I'd taught, like, four years or so. One year off, no problem. There was an elderly professor, Richard Sutton, who had been at Haverford or some East Coast school. Candidly, there were some problems. It felt like Caltech was not properly reaching the introductory students because there was a big dropout rate. And the people who were teaching the sections were either TAs–some of them good, some of them not so good–or faculty members who kind of didn't take it seriously.

Now, that wasn't true of Robert Leighton. He was really interested in teaching. But apparently, there was some question overall. They hired Professor Sutton, who had a national reputation, in AAPT. He was in his late 60s. Caltech hired him to help beef up teaching introductory physics courses. Anyway, several weeks into the semester, probably 1966, they said, "Professor Sutton is sick. Would you be willing to take over his classes until he gets well?" And I said, "Sure." Because I'd been teaching those classes for a while. No problem. But he died, so I wound up teaching his section for the entire year. Even the one year that I wasn't going to be doing teaching, I wound up teaching.

ZIERLER: What were your motivations in the early 1980s to become a registered professional engineer for the state of Colorado?

ZAIDINS: I'd just gone through a divorce, and I was poor. [Laugh] I had two kids. Child support, alimony. I'd been teaching engineering students, and as an experimentalist, you design equipment, you do stuff. It's basically engineering. The whole Society of Professional Engineers, I had met all the criteria, pretty much. But you have to have, at least in those days, the 80s, two people vouch for you, then you have to take all these tests. Well, the tests, for somebody who'd been teaching engineering, were easy. I just decided, "This could be something. I could do some consulting on the side to help me put food on the table." I decided, "Okay, why not do that?" I did. Have I ever been able to really use it? No. But yes, I am a registered professional engineer.

ZIERLER: Tell me about how you got involved in academic administration, leadership, at CU Denver.

ZAIDINS: It's something I didn't want to do. I was asked to be a dean and I said, "No, I never, ever want to be a dean." Caltech is probably different, but at most schools, unless you have ambitions to become an administrator, you are not excited to be a department chair. "As a good citizen, you have to spend three or four years being department chair, and then you can go back and do the stuff you really want to do." And that's pretty much the way I looked at administration. That last five years (2015-2019) was really an unusual situation. When you have the department that's so dysfunctional, that they can't even choose a chair, and you had to have a chair from psychology who's acting chair of the physics department, you have somebody from math who's acting chair, you have somebody from geography who's acting chair, it was a mess.

They did the unusual thing of going to get the old guy and saying, "Would you be willing to come back?" When I was asked to come back, I said, "This is an associate dean asking me to do this. You better talk to everybody in this department. If there's any one person in the department who does not want me, then this is completely off the table." Because I loved living out by the Pacific Ocean, I was reluctant to leave. As it turns out, it probably was the right thing to do. And the department is now in really good shape because we hired a really good, age-appropriate department chair. So no, I never really wanted to be a dean. I mentioned that Willie Fowler came to Colorado to give a talk, and he always started his talks with something humorous.

This one talk that he gave, I remember this very clearly and will try to do it justice, Willy said, "People have asked me why I never went into academic administration, why I wasn't a dean. It's something that never interested me. Here's an example. I went into the restroom, and I was washing my hands. And instead of towels, you have these hot air dryers. And right by the button, it says, 'Push here for a one-minute talk from the dean.'" [Laugh] That's a Willie Fowler joke, his explanation for why he never wanted to go into academic administration. Of course, he did have pretty high–I don't think he was ever even a department chair at Caltech, but he was on all kinds of national advisory committees and stuff like that. I can't remember who it was that told me, maybe Ward Whaling, maybe not, but because of the work they did during World War II on the proximity fuses for the torpedoes, he had a real in with the Navy.

And our laboratory, when I was a graduate student, anyway, was funded by the Office of Naval Research. He was on a lot of advisory committees in Washington. And he was particularly troubled during the Vietnam War because there was a periods there when he was not his usual self. One of the other faculty members, and I really don't remember who it was, and they've all passed by now anyway, was really having a hard time associated with whatever it was he was involved in during the Vietnam War. That was during the period I was a graduate student, the height of the Vietnam War.

Physics Curiosity and Just Ask Clyde

ZIERLER: Your interest in public communication and bringing physics to the broader community, the Just Ask Clyde project you worked on, was that in retirement or when you were an active professor?

ZAIDINS: No, that was in retirement. We had a speaker's bureau, and somebody wanted somebody to talk on astronomy or something like that, I did a fair amount of that. But Just Ask Clyde was a very different kind of thing. When I retired in 2004, the first time, it was not clear that we were going to be able to keep our university emails. My wife passed away last year, but she was a really good IT person. I mentioned she was the one who got me into putting my lecture material, tests, and things online. She said, "I'll create a website for you so you will have email if the university cuts you off from its email." She came up with JustAskClyde.com.

ZIERLER: What's been fun and meaningful about being able to do this for you, the physics questions and the answers that you get?

ZAIDINS: Oh, it's just nice to engage with people who want to ask good questions. It's fun. I belong to a group of people that are interested, very rational people. It's called the Secular Hub here in Denver. Every Sunday morning, we have breakfast. For those of us who don't go to church, we congregate. And there are, like, 40, 50 people there. There's a table called the nerd table. It wasn't intended to be that way, but we nerds tend to self-congregate. There are some really good science discussions at those tables. Not all the time because sometimes we talk about other things. It just depends. Recently, one of the people who belong to this group worked with Scouts. There was a kid, about 11 years old or so, who was really interested in science. Jesse, the fellow, probably early 20s or 30s, brought this kid, and he was asking really good science questions. That was kind of fun for the Sunday morning get-togethers.

ZIERLER: Have you kept up with the research at all? Do you stay current with any literature?

ZAIDINS: Some. There's a lot of stuff that I haven't really kept up with. There's just so much. If something interests me, then I'll dig into it. I've actually gotten interested in a medical issue. Just very briefly, sepsis is a very serious medical problem. A lot of people die from sepsis and septic shock. There is a prevailing theory that sepsis is caused by what's called the cytokine storm. It's bullshit. And there's a very bright medical doctor here at the University of Colorado (Leland Shapiro, MD) who has been fighting an uphill fight because although it makes sense, it's wrong. And until people decide that there's no evidence that this is actually not what causes sepsis, they're not going to treat it correctly. Ever since the belief that the cytokine storm causes sepsis came around, there's been no improvement in treating people. A lot of people die from sepsis. This person has been publishing papers, and like I say, for him, it's an uphill fight.

But I happen to know him personally, and he's so persuasive, and he has so much data that shows that people have been ignoring the fact that this isn't working, it's wrong, and there's a much better explanation. But because the administration of medical research is in the hands of a powerful clique, it's very hard to show that this is the wrong direction. So much money is being spent on research trying to show that it works, and all the experiments fail. And they always come up with an excuse for why it didn't work when, in fact, the real excuse is that the whole theory's wrong. Anyway, that, interestingly enough, is basically what I've been spending time on. [Laugh]

Luck is a Nontrivial Factor in Science

ZIERLER: For the last part of our talk, I'd like to ask a few retrospective questions about your career, and then we'll end looking to the future. Being so lucky to be part of that cohort at Caltech, if you've ever reflected, why Caltech? Why this little school in Pasadena that was such a research leader obviously in this field, but in so many other fields? I wonder if you've ever thought about that.

ZAIDINS: Oh, yeah. A lot of it has to do with luck. I hate to say that, but getting the right people together at the right time. And people had vision. Hale, Millikan. I know Millikan is now–I suspect that what they're doing in removing his name from so many things is probably the right thing to do, but Caltech wouldn't be there without Millikan, and Hale, and people like that. Thomas Hunt Morgan. All of those. Somehow, we got the right people together at the right time, and that brought more people like Linus Pauling. It was 1950 before we got Feynman. And that attracts people. Why did Kip Thorne go to Caltech? 1955 article in Time Magazine. Why did Clyde Zaidins go? I shouldn't even call myself in the same breath as Kip Thorne. [Laugh] But Kip was a real person. He was an undergraduate student just like me at the same time. Just turns out he's a lot smarter than me. [Laugh] There obviously were an awful lot of people that came because of that one article. It got people from all over the country. If you're from California, yes, you'd know about Caltech. But if you're from Cincinnati, Ohio, Caltech–"Oh, hey, that's where I want to go."

ZIERLER: From your time there, for the research that you've done as a professor, what do we understand now about nuclear astrophysics that we didn't when you became a student?

ZAIDINS: There's actual experimental verification of some of our theories. You could argue that the fact that we got carbon and oxygen here on Earth is experimental verification, but it goes beyond that. There are two of the lighter chemical elements that have no stable isotope, technetium and promethium. When you get past uranium, all of these are radioactive. But up to approximately the uranium part of the periodic table, all of the elements have stable isotopes except for technetium and promethium. And they've been produced artificially on Earth, so we know what their properties are. Even though we can't go to a mine and find them, we have to make them, we have studied them, we know their chemical properties. We know their spectra. If you see promethium and technetium spectra in stars, and we know their half-lives are much shorter than the lifetime of the star, this is pretty strong evidence, I think, of overwhelming evidence that they're being produced in the star.

ZIERLER: Which tells us what? What's the takeaway?

ZAIDINS: That there are nuclear reactions going on in stars. Which is sort of obvious, but it's nice to have actual real verifications. If you have technetium in the star, it couldn't have been there when the star was formed because the star was formed way before the half-life of technetium existed. One other thing is that supernova 1987-A, which is the nearest supernova since 1604, we actually saw the gamma ray spectra of those very short-lived, less than a year long, half-lives that we predicted would be found in a supernova. We actually see the gamma ray spectra of those. Pretty much the basic story was told in the mid-1950s. But a lot of it was conjecture, a lot of it was based on existing data at that time, but we filled in a lot of the blanks with more accurate details.

ZIERLER: Last question, looking to the future. What have been some of the key lessons for you in never making that 100% choice between research and teaching, in being able so successfully to blend the two? In other words, how has research made you a better teacher, and how has teaching made you a better researcher?

ZAIDINS: In terms of teaching making me a better researcher, if you're going to give a lecture or a course, you have to build something from scratch. You can't just go in and assume that your audience knows the background. You have to start at square one. Now, there are going to be students that it's going too slow for. But basically, I think it helps you organize how you teach, and then that's going to affect your research. The research affecting the teaching is the excitement of discovering new things. Just measuring stuff that's never been measured before gives you a certain enthusiasm when you're talking to your students. I'm making it sound simpler than it really is, but it's that feedback between the two that makes that difference.

ZIERLER: I want to thank you for spending this time with me. It's been a wonderful conversation. It's very special for me to get that window into Willie Fowler and Kellogg Lab from the 1960s. It was a magical time, and it's great to have your perspective.

ZAIDINS: Oh, yes. I feel really lucky that I was there at that time. In sort of the same way, when I first came to CU Denver before it was CU Denver, we were so small, everybody knew everybody. And now, we're a big campus. I don't think it's even possible to have the same kind of camaraderie that you have with a much smaller group of people.

ZIERLER: Thanks again, so much.

[END]