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Marvin Wilkening’s Interview (1995)

Marvin Wilkening was a physicist whose work took him through the Grand Circuit of the Manhattan Project: Chicago, Oak Ridge, Hanford, Los Alamos and Trinity. He worked closely with Enrico Fermi and describes his deep respect for Fermi’s intuition. In this interview with a former student, Wilkening discusses his involvement with the Manhattan Project and what his thoughts were when witnessing the Trinity Test. He explains his work during the Trinity Test to estimate what percentage of the fissionable material actually took part in the explosion. He finishes with a discussion of teaching physics.

Date of Interview:
September 12, 2022
Location of the Interview:


[Many thanks to Thomas Scanlan for recording and donating this interview to the Atomic Heritage Foundation.]

Thomas Scanlan: —Is part of an interview, which I held with Professor Marvin Wilkening at his home on Socorro, New Mexico on July 15, 1995. 

Now, I was reading that you had worked at four different places associated with the Manhattan Project.

Marvin Wilkening: That’s right.

Scanlan: Was your first work with [Enrico] Fermi at Chicago?

Wilkening: At Chicago, and that was the first reactor there at first. That was a splendid experience.

First the subject, an opportunity for just a graduate student to get into that scene, and then for a chance to get to know Enrico Fermi. What a wonderful personality he had, as far as getting things understood and people on their way. It was all around just a wonderful experience to be there, and get that opportunity.

That was my introduction to applied nuclear physics and [inaudible] reactors and just the way the war and everything went. Since I monitored, actually built the detectors for neutrons, they said, “We would like for you to go to Oak Ridge, Tennessee, and start up down there.”

“Okay, sure.” I packed up.

Scanlan: Now, when was that?

Wilkening: When?

Scanlan: 1943, or thereabouts?

Wilkening: Well, let’s see. It was about ’43, yes, when we went to Oak Ridge.

Scanlan: Were you at the time when the reactor went critical in December ’42?

Wilkening: Yes, there in Chicago.

Scanlan: You were there?

Wilkening: Yes.

Scanlan: That is something.

Wilkening: Yeah, that was in September [misspoke: December]. Then we stayed there until right after the first of the year. That’s when [inaudible] to Oak Ridge.

It just happens that I grew up in Oak Ridge, Missouri, so I went to another Oak Ridge. [Laughs] I couldn’t believe it. Then, after that was the rather large air-cooled reactor. That time they really wanted to get going on the plutonium production, which was really what they were after. Then they had the big one set up around in Columbia River in the State of Washington, Hanford Engineer Works.

I got this underway, and everything seemed to be going really well. I said, “Well, I am going to go back to Chicago,” [inaudible].

But then at the last minute, “We have got another thing. We have got to send you to Site Y,” and that turned out to be Los Alamos.

One morning, they said, “We are going to go to the test in the desert down south.” So I came by Socorro, New Mexico, and on down here about ten miles, San Antonio, to the east. I had to decide where. We called it “Trinity,” and it’s still making the headlines all these years later.

It was just a good experience to get out in this country, and have the neutron counters work with the technical and all that stuff.

Scanlan: What was the technology then in counting neutrons? What was the basic reaction?

Wilkening: It was really straightforward. We used boron trifluoride, in the gas, in the counter. The neutrons caused the boron atoms to split and leave a nice pulse. So by using a proportional-type counter where you could rule out the lower level ones and get the big pulses, count them, and that was directly proportional to the neutrons, formed by the neutrons acting on the boron. That was it.

Scanlan: I know with the old Geiger tubes, there was kind of a plateau you had to tune it for, to get the voltages right. Did you have that problem with the gas you were using?

Wilkening: Yes. In fact, we operated in pretty much that same way, because the ionization that came from the splitting of the boron atoms, same idea. That was my size pulse compared with just casual gamma ray out there, electrons [inaudible]. That’s what we did.

Scanlan: Now, what time did you get to Los Alamos, then? Was that in the summer or spring of ’45?

Wilkening: Oh, let’s see, in ‘43 I went to Washington. It was early, like April or May. We were going to go to Chicago, and then at the last minute, Los Alamos. We got to Los Alamos around the Trinity test. They set up. Well, they had done a lot of laboratory and field and some area testing, but this was to be at the White Sands Missile Range, which helped [inaudible]. 

Scanlan: Where did you set up your test equipment for the neutron counting?

Wilkening: Actually, where the tower was and the site was about six, nine miles south and east of the entryway, the gate, up there on the top by San Antonio, east, 380. Then you could see the hills to the south. That’s kind of the rim on the Jornado, and you could see this big flat. It was down in there about six miles. The big tower there, that’s where they sent this Jumbo.

Scanlan: Not a good idea, was it?

Wilkening: No. [Laughter] So anyway, that’s was the morning of the 16th is the big bang. 

Scanlan: Were you measuring prompt neutrons then with those detectors, or the actual burst?

Wilkening: No, at that time, we had gotten to the point where if you want the major neutrons, but also such that had been through Hanford upgrades and whatnot. If you had a good detector system for the gamma beta ray system then you could imply very readily what the neutrons, whether you could read those directly or not. Well, we did have a [inaudible]. So we were set up down there. General [Leslie] Groves and—what’s his name?

Scanlan: [J. Robert] Oppenheimer.

Wilkening: Oppenheimer, they were right on up from me, about 400 yards or two.

They gave you that little spot [inaudible]. Little tables under it to put work, which [inaudible].

Scanlan: Yeah, you never know sometimes. Taking place, like this thing here.

Wilkening: Oh, I will say, right.

Scanlan: Yeah, Murphy’s Law has been around a long time.

Wilkening: Yeah, oh Murphy’s Law, yeah.

Scanlan: Anything that can go wrong—

Wilkening: It will. [Laughs]

Scanlan: Yeah and there are variations of it, but that’s a classic. All physics students encounter that in laboratories.

Wilkening: [Laughs]

Scanlan: I know that physics labs were a real kick sometimes. You knew what was supposed to happen, but sometimes it just didn’t.

Wilkening: Yeah, and of all things from what you heard in the school system, all about physics and what a specific science it was. Then, you have strange things happen.

Scanlan: Of course, it’s from the things that don’t work right, I think, that you learn a lot.

Wilkening: Oh, sure, absolutely.

Scanlan: Because then you have to kind of dig in and say, “Okay, what happened?”

Wilkening: Right, exactly. Yeah, every physicist has been through that. 

Scanlan: Now, did you teach the full forty years at Socorro? Or were you a dean part of the time or a teaching dean toward the end?

Wilkening: Oh, I was when John [inaudible]. I stayed on those early years mainly teaching, but also I made it pretty clear that I wanted to have some time and access to somehow to do some research, because I wasn’t going to get in to just a purely teaching scene. They understood that, so I had time to do research.

What I did was add-on to the radon and detection, that sort of thing. Actually, when I was down here, I really emphasized that part, because I had the opportunity to have outdoor access and high-level measurements up there on the mountain.

Scanlan: Magdalena?

Wilkening: Langmuir Labs.

Scanlan: Langmuir.

Wilkening: So all that fit in really in the environment in which to do that. So it was pretty largely outdoor radon.

Scanlan: Now, when you went back to Illinois, is that where you met Ruby, at Illinois? Or did you meet her out here?

Wilkening: Actually, actually, she was in Missouri. I met her when I was a student. I finished my undergraduate work there. In Chicago, I did graduate work there. About a half year, then we took time to get together and so we got married. She [inaudible] where her dad, and the mayor. So that was it. [Inaudible]

Scanlan: You have had your fiftieth anniversary already then?

Wilkening: Oh, yeah.

Scanlan: Looking forward to the sixties.

Wilkening: [Laughs] Yeah, I like that.

Scanlan: Now, what because I am sure driving through town wasn’t the reason, what decided you to come back to Socorro from Illinois?

Wilkening: Well, I will say the fact that my old professor from Southeast [Missouri] State was here.  He got me interested and said, “We would like to get together and make you a job offer.” So they did.

It was mainly the opportunity to do research, which in just a relatively small college, is just teaching. It doesn’t necessarily mean that you can do that. By that time, I had gotten along. I knew some of the people at NSF, National Science Foundation, and later at Department of Energy. They through the years were very good financial support, NSF. They could do it and did it through Tech here, in some respects better than in a big university. So overall, it worked out fine.

Scanlan: On the morning itself—I just have to ask you this question. About the time this [the Trinity Test] went off, the light and everything, that has been very well described. What were you thinking about for those first few minutes right after the explosion?

Wilkening: I thought of that before. I think it was the level of intensity for getting things to work, getting samples, then tag up their back. [Inaudible] So it was all of that. The big bang, and there were still a lot of work. Are things working? So I had to check out everything after the big bang.

Sure enough, with a little encouragement here and there, it seemed to be working. That was great. So I was all set to make an analysis of what fraction of the thing actually underwent fission, all of that. Of course, that’s not an easy way to note the fraction.

Scanlan: That’s interesting that most people guessed the yield low. A typical conservative physicist.

Wilkening: Yes, it’s like five percent or so instead of twenty, which was closer to what was actually going on.

Scanlan: Fermi’s famous experiment with the piece of paper.

Wilkening: Oh, yeah.

Scanlan: Even that came out a little low.

Wilkening: Yeah, yeah. [Laughs] Oh, that was terrific and so typical of him, Enrico Fermi.

Scanlan: The back of envelope approach.

Wilkening: Yeah, oh yeah.

Scanlan: Amazing.

Wilkening: Oh, there was just there were so many occasions where he would pull little things like that out. [Inaudible] spend an hour thinking about it, and it came too.

Scanlan: Was he pretty easy guy to work with then, at Chicago?

Wilkening: Yes, he was indeed. He could see through or think through the physics and the patterns of that one would to have to follow.

Scanlan: Do you recall meeting Richard Feynman?

Wilkening: Oh yes, yes.

Scanlan: He would have been about your age?

Wilkening: Yes, I met him at the University of Chicago. I went up there [inaudible] teacher, but I went back to the university. For one period, Feynman had a short series of research lectures. I got a small group of people to attend. I got to know him. He was talented.

Scanlan: A little oddball. He has written some interesting books. 

Wilkening: Yeah, that’s right. Exactly.

Scanlan: One reason I ask, he wrote the Feynman’s lectures, one, two, and three.

Wilkening: Yeah, yeah.

Scanlan: We tried to use those, and found they were just—the average student couldn’t deal with them because they were a little too tough.

Wilkening: Yeah, I would kind of think so.

Scanlan: So I think Halliday and the Resnick was our primary.

Wilkening: Yeah, Halliday and Resnick was one.

Scanlan: And Sears and Zemansky, I mean it was one or the other and they were good, both very good. But the Feynman lectures were—oh, they were wonderful to sit down and read, the parts of it I understand, but it was just it didn’t work with our students. We made a very brief trial. I guess they even used them in some physics graduate classes, especially the third volume.

Wilkening: Uh-hm. He had some very good things.

Scanlan: Interesting guy.

Wilkening: Yeah, very interesting guy.

Scanlan: He was, I guess, a little bit of a cut-up at times, too.

Wilkening: Uh-hm, yeah, he was. [Inaudible] Every day, he attracted people. That’s good to have people [inaudible] 

[Tape switch.]

Scanlan: —Teaching any of the beginning physics classes your last few years when you were teaching? Did you still teach sophomore physics, do you remember? Or was it only advanced students?

Wilkening: I tell you, the last few years at the time I would have burned the books [inaudible] but I stayed on. They wanted me to. At the time, I had [inaudible] teaching. So yes, I did teach, but in those latter years, not general physics. [Inaudible] But later, things that had to do with the nuclear physics and special research and things [inaudible].

Scanlan: Did you find that there was any change in the quality of students, say between the 1980s and the 1950s or ‘60s? Better, worse, same? 

Wilkening: I guess I would have to say essentially the same. In the later years, there got to be an effort [inaudible] to make a bigger effort to get to the schools and programs to recruit, but that was a stronger effort. I had visits to schools [inaudible] is what we have got, radioactivity, what you have been breathing all day, take a sample there [inaudible] and see how radioactive it really was, but anyway, that kind of thing [inaudible]. So it was interesting to me, a chance to get the word around and recruiting and teaching, so a little of all of it.

Scanlan: Do you recall what book you used? Was it Sears and Zemansky, or Haliday and Resnick back for your early physics classes? Do you remember what textbook you used?

Wilkening: No. There were some others.

Scanlan: Well, Sears and Zemansky has been around forever.

Wilkening: Yeah.

Scanlan: I was trying to remember myself what—

Wilkening: [Inaudible] 

Scanlan: That was a big, thick, red covered one. It’s in about six or seven editions now or more.

Wilkening: Yeah, that covered university physics.

Scanlan: I just wondered if you remembered. That was kind of a classic. I know that was used back then, not that far back.

Wilkening: I think the books for general physics were pretty well improved through the years. There was an effort to bring up both the standards and the way it’s presented. Then you could have that as a base of what I said to them. It’s not necessarily what they offered in the textbook, science, but the basic subjects, the laws of physics and all. [Inaudible] the teachers still present these subjects. So I thought that was a very good thing about physics textbook. There were mechanics [inaudible], lots of ways of presenting it that you could add to. But I thought it was a good subject for the most part, the books and materials were generally pretty good. 

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