Nuclear Museum Logo
Nuclear Museum Logo

National Museum of Nuclear Science & History

Ben Diven’s Interview

Manhattan Project Locations:

Ben Diven discusses helping set up Los Alamos for the Manhattan Project and working on instrumentation for the atomic bomb. He speaks highly of J. Robert Oppenheimer’s leadership abilities and the colloquium Oppenheimer began to allow all the scientists at Los Alamos to discuss problems and exchange ideas.

Date of Interview:
April 8, 2003
Location of the Interview:


Ben Diven: All right. I’m Ben Diven. That’s spelled D-I-V-E-N. I was born and raised in northern California, and I went to school in my hometown of Chico, and fortunately there was a state college there so I could start college in my hometown. I took the two and a half years of physics and mathematics that they taught there. And then, after a break of a couple years to save enough money to be able to go to Berkeley, I then transferred to University of California at Berkeley. 

I then finished up then with a Bachelor’s degree in physics in 1941 and started graduate school that year. And, of course, then December 7 of 1941 came very quickly. But I went on, finished that semester—that year of graduate work. By then all of my friends were in the military and I knew it would be a good idea for me to be also, so I went to join the Navy. But they said they couldn’t take me until I quit my job; I was essentially a teaching assistant at that time at Berkeley. So, I went to the chairman of the department, I announced I was quitting, and a little later I was told to go see Oppenheimer. 

I didn’t know Oppenheimer personally—I’d never had a class from him—but he told me that if I wanted to be in the military he was going to be in charge of a project and all of the people working on it were going to be in the Army. So I could be a second lieutenant in the Army and still be doing something that he assured me was more important than what I would probably end up doing in the Navy. So I said all right, I’ll do that. And then, well, things were delayed and months later he stopped me in the hallway of the physics building and said well, things were different. We weren’t going to be in the Army after all but it would still be important work. We’d be living on an Army post and he thought I should continue, so I said well, all right, I’ll go along with you. And then, after considerable delays, finally, in mid-March of 1943, Oppenheimer asked me to go along with some other folks to Los Alamos. 

At the time there was no housing, no laboratory buildings finished, and Oppenheimer was having trouble getting real information about what the schedule was going to be. So he sent—there were four of us, Joe Stevenson, who was a Santa Fe lad and knew the area; Hugh Bradner, who had just got his PhD in physics; John Williams, who was a well-known professor of physics at University of Minnesota; and I, the lowest of the low, a mere graduate student, came along. 

I arrived in Santa Fe on March 13. Then we split up into two groups. Joe Stevenson and Hugh Bradner went looking for housing. There were no houses on the hill. The project was behind schedule. Other projects at various universities had been shut down and the people told to come here, but nothing was ready for them, so first was to find a place for them to live. Some of them said they’re coming anyway and so they would be arriving and no place for them to live. They then began to confiscate dude ranches, they took over all the housing at Frijoles Canyon, Bandelier National Monument, and any place they could find housing, they took. 

In the meantime, John Williams and I came up to Los Alamos every day. There were no telephones on the hill, there were no laboratory buildings finished, there was no housing. So what we did was to go among the workmen, talk to electricians, plumbers, carpenters, and so on—these were the people who knew when buildings were really going to be finished. So we would talk to them, get what information we could, John Williams might try to hire a few of them away to work for the lab after their jobs were finished, but every evening we went to Santa Fe, where we were living in a hotel, and called Oppenheimer, who was still at Berkeley, and told him what the situation was. Frequently we’d find things which were just obviously wrong. The building specifications didn’t, for instance, give any place for a control room for the cyclotron, and the control room couldn’t be alongside the machine because of radiation problems. But this kind of thing we could easily spot again. We’d telephone Oppenheimer, tell him what we’d found out, and then he’d fix it. 

So that was my earliest days in Los Alamos. You can imagine that, in mid-March, it was dry and dusty and wind was blowing. Hundreds of workers were tearing up everything in sight to build new buildings. It was quite unpleasant, but it was also very exciting because there was so much happening, and we knew by then that all of these people who were insisting that they were coming, even though they didn’t have any place to work. But that soon cleared up and there were some laboratory buildings being finished. 

Oppenheimer had arrived and what immediately turned out to be a big problem was that there were tons and tons of equipment being shipped to Los Alamos and there was no warehouse. So it just happened there was one building that had no use and it was the first building finished. It was the building to handle liquid deuterium to build a hydrogen bomb because Teller insisted that it had to be ready to build one. But, since everybody knew that was a long-term project, the building was just empty, so we took it as a warehouse. 

Oppenheimer asked me to do something about all this equipment arriving because the people who were going to be in charge of shipping and receiving and such things, the people who were experts on that kind of thing weren’t going to come for a month or two. So I inherited a building that had, in the middle of an empty floor, a great huge pile of boxes and things that were coming in everyday by truck. And, at the same time, here were all these scientists coming in and their labs were just being finished, so now we had to get all this stuff distributed among all these people and since there was nobody to do this, the answer was that the scientists themselves had to turn themselves into laborers. And they would come and get their own equipment and haul it to their laboratory and start setting it up. 

And, this period, there were not only little boxes of supplies for laboratories, but there were also huge machines, like a cyclotron being—was dismantled at Harvard and shipped here. There were Van de Graaff accelerators from Wisconsin, Cockcroft-Walton Accelerators from University of Illinois. These things were all arriving, some of these were enormous objects, but they were all, amazingly enough, getting assembled in very short order. 

It was pure chaos for weeks and then gradually everything began to smooth out. Everybody was working day and night getting things put together. And finally, in a month or two, there was a laboratory working. Even accelerators accelerating beams or protons, something that would normally take years to do, was done just in a matter of months. And it was really quite an amazing thing, also very exciting. 

All kinds of strange mishaps were going on all the time, but, well, enough of that. The laboratory was already functioning. The experts who knew how to do things about purchasing and shipping and receiving, and so on had arrived, and Oppenheimer assigned me to a group in charge of Bruno Rossi, who was an eminent Italian physicist. He told me that this group would be the place where I would learn the most of use to me and he was exactly right. It was a wonderful experience. 

Our job was to develop instrumentation that was needed for making the measurements that we didn’t—that had to be made before we knew how to build a bomb, so I think I should divert now and just say a few words about how we thought the bomb was going to be built. 

The idea is that if you have enough fissionable material, and it is all assembled in a solid mass, it will be an explosive, but it has to be assembled rapidly so it doesn’t just simmer as it approaches criticality—it has to go from uncritical to supercritical very rapidly. So the idea was that we’d just have a, let’s say, a large mass uranium-235 with a hole in the middle of it that would be just not quite critical. And then you would put the matching, missing piece into a very powerful gun and shoot it into the center of this mass of fissionable material. And it turned out that that was a very practical idea and a navy captain who was an expert on all kinds of munitions was sent here to be in charge of developing the gun that would do this. So, as the scientists arrived they already knew how to put this thing together except for a few bits of missing information. 

One bit was they didn’t know how much material it would take to make a critical mass, so there were still some experiments to do to clarify that. Also, to use as little material as possible to make a bomb, you’d need to surround the fissionable material with reflecting materials that would scatter neutrons back into it instead of allowing them to escape, so there were a lot of measurements to be made before they really knew how much material it would take to make a bomb, but that was very quickly underway. 

In an amazingly short time, the experiments were underway to make these measurements and the idea of what a critical mass would be, for instance, was getting narrowed down more and more every day. So everything was going along beautifully in designing these weapons. 

We knew that there was going to be both uranium-235 and plutonium. It turned out there wasn’t going to be very much U-235 so that wasn’t going to make any but one bomb, and that wasn’t enough. But we were going to have plutonium just pouring in, so that was still all right.

It was when taking some point a higher velocity projectile for the plutonium but still it was all practical and the plutonium gun was also designed and would soon be ready to go. Until Emilio Segrè, another Italian physicist, discovered a property of the plutonium that was going to be shipped to us that made it impossible to use that in a gun-type weapon because you could not shoot a projectile fast enough to assemble it rapidly enough. And so they—it was necessary to go to an implosion system, use high explosives to collapse, for instance, the shell of plutonium. Then, we didn’t know how to do that, so Oppenheimer reorganized the lab and most of the physics division went into studying implosions, and that included the group I was in. So then for nearly a year we studied methods of making—imploding a device. 

Of course we couldn’t use plutonium, we didn’t have any, but we used mock-ups, mock-up metals to try and get a perfect implosion—turned out to be much more difficult than expected. In the beginning it was thought that about fifty scientists and engineers would be all of the staff needed to do the work to get these bombs designed and built. Once we had found this problem, it became obvious that it would take many times more people than that. So not only did the laboratory turn itself upside-down internally, but hundreds or thousands of people had to pour in to make up for the lack of personnel to tackle this much more difficult problem. 

So then we worked on this problem, along with many other groups, until the implosion system was reasonably perfected. And at that point we went into the next job, which was to measure what goes on in a nuclear explosion on the first test. Now, we did not test the plutonium—excuse me—we did not test the uranium bomb because there was only enough material for one. But besides, people were very confident that it would work. At least, if the plutonium bomb would work, then you could be sure that this simpler uranium bomb would. 

So they tested the plutonium bomb and our group set up an experiment to measure the progress of the nuclear explosion. And then, as everyone knows, that bomb shot was very successful. That guaranteed to us that the war would be over very quickly and I went home for the first time, and this was in the summer of ’45. So I was there when the bomb was dropped on Hiroshima and then I rushed back to the lab because I wanted to have all of the news of course. So that’s the end of the story. If you have some questions, you could ask.

Cynthia Kelly: Sure. You obviously, in starting at Berkeley, knew Ernest Lawrence.

Diven: No, I didn’t know Ernest Lawrence. He didn’t teach any classes; I never had any classes from him. I knew him when I saw him.

Kelly: What was the impression you gathered from the hallways, or some other faculty or students?

Diven: Ernest Lawrence was not a person that people knew. He was too much of a big shot, and I don’t think he was the kind of a person who really wanted to get to know students. He probably would have taught if he had. 

Oppenheimer was the opposite. He was totally wrapped up in his teaching and he loved his students. And, of course, I wasn’t a student of his but I did get to know him, especially in the beginning of this project, and I always felt that he was someone who had a real interest in every single person that he was involved with.

He was amazing in that he remembered people’s names and faces; if he had only seen some technician once he would remember that person. And, of course, he also prowled the hallways at night to drop in on laboratories, see what people were doing, and he remembered what they were doing. So everybody had a feeling with Oppenheimer that this was somebody who really cared, and it made working here just, well—you could almost call it a pleasure even though it was much harder work and more frantic than anything we had ever experienced before, but we had a real feeling of belonging.

Kelly: Do you think that it was really Oppenheimer’s leadership that helped people give that feeling of belonging?

Diven: Oh, of course. As a matter of fact, scientists are just as vain as anybody else, and you have all these brilliant scientists, each one of whom is sure he’s smarter than any of the others—they’re not necessarily the easiest people to persuade to work on what, let’s say Oppenheimer thinks they ought to be working on. But he was very, very good at getting all these people to work together instead of squabbling among each other.

Kelly: What were some of the techniques he used to achieve that? How did he succeed in that?

Diven: How did Oppenheimer?

Kelly: Yeah. How did he make everybody feel part of the team?

Diven: He’s just a very, very clever man who really cared about people, so that he seemed to understand—if people wanted to do something differently than—seemed to be the right thing to do, he seemed to have a knack of persuading them of what really would be best. But, on the other hand, it was probably mostly a matter of really of letting these people to do what they thought was most important, because usually they were right. He did allow an enormous amount of self-determination and, let’s say, especially among group leaders. Now, a mere student would mostly be doing what he was told, although even there, a lot of students who came up with good ideas—not necessarily people already with their PhDs, but people who had just come as students—did come up with important ideas.

Kelly: I’ve also heard that the colloquial gatherings that he had were very important—that people would contribute even if they weren’t involved like Johnny von Neumann, who supposedly contributed to the idea of the implosion device, and so forth.

Diven: Yes, that’s right. I think the colloquia were one of the most important things.  Everybody who was a staff member at the lab was allowed to come to colloquium. And I don’t know how many people, I suppose it was some hundreds, and Oppenheimer insisted that everything could be discussed there. There were no compartmentalization and it was very often true that people who—well, the idea was to have various group leaders usually describe what the group was working on and what their main problems were, what they were having trouble with. And very frequently then it would turn out that somebody who had not associated with them at all would come up with an idea of something that would actually be important. 

One thing that I remember especially: now, in general, it would only be technical people who would be staff members who would go to colloquium, but Oppenheimer was smart enough to know that he wanted to have some representative of all parts of the lab there. For instance, the superintendent of the machine shops was to have complete access to all information and he attended colloquium. So when an explosives expert was talking about the difficulties of casting explosives—because you cast it as a liquid into a mold that is the shape you would like it to be but then it shrinks, so now it’s no longer quite the right size or right shape—this machinist just got up and said, “Well, obviously what you need to do is cast it oversize and machine it to the right size.” And the explosives man just pooh-poohed that, “That’s absolutely impossible, that cannot be done,” but enough people realized that’s what had to be done, thats that’s what was done. 

Soon after, all the explosive lenses were being machined and I believe that not a single machinist was ever killed at Los Alamos while machining explosives. There have been deaths from explosives and accidents, but not because they were machining it. Of course, it had to be done with great care. But anyways, that was just one example of why a colloquium was so important. Usually the solutions to problems that came up were very, very technical and required a lot of scientific knowledge, but not always.

Kelly: That’s a wonderful answer. Thank you.

Cameraman: We need to change tapes.

Diven: Well, we’ve probably beat this one to death anyway, haven’t we.

Kelly: Well that one. That is terrific, though. Do you have any observations about General Groves or…

Diven: No, such as I would never have had much contact with General Groves. I did sit next to him at lunch one time, but that isn’t where you get great amounts of insight. Although, he did tell me all about how he knew from the beginning that it was not going to work with fifty people.

Kelly: Is that right?  

[Tape switch.]

Kelly: Are we ready? Okay. I’ll just ask a couple more. Maybe you can tell us about how much you knew about the overall project?

Diven: When I first arrived, I only knew what the object was: to build a nuclear weapon. But as soon as most of the original staff got here, which was—I don’t remember when, but probably sometime in April—but Oppenheimer had Bob Serber give what he called a series of lectures that was—ended up being written out and was called “The Primer.” This was a primer on how to build a bomb. So that was a series of lectures, simply outlined everything we didn’t know but had to learn before the bomb could be built and all of the main problems. So by the end of that series, then everybody had a good general idea of what it was all about. 

Of course, Oppenheimer and all his major staff were professors. They lived to teach, so as soon as the lectures of the primer were over, then, started classes, so there were classes in nuclear physics, classes in instrumentation, and so on, that went on all the time during the war. And many of these lecture notes were then used by other teachers, when they went back to teaching again, to teach their courses from. The entire period was a period of education.

Kelly: So how hard did you and your colleagues work during the Manhattan Project, especially before the end when the Trinity device was getting ready?

Diven: Well, I don’t remember there ever being a let-up. It seemed like we were always pushing, and there always seemed to be one more crisis, like the plutonium crisis, something always happening that, no, this isn’t as easy as we thought it was.

And in general, well of course there was a nominal work week—and I guess it might have been a forty-hour work week, no, it couldn’t have been a forty-hour week—everybody worked six days, at least—and most people worked far more than eight hours a day. It was normal to—well, at least for single people, like Becky [Diven] and me. We’d eat at the Army mess hall and it was open at certain hours, so you would break for lunch and dinner, but then you’d go back to work after dinner.

Kelly: So what time did you finally quit?

Diven: Well, it depended on what you were working on. Actually, I suppose there must have been periods when everything seemed to be going smoothly and we didn’t have to work very hard. For instance, when we were working on implosion systems, this involved using extremely powerful radioactive sources that decayed rather rapidly, so there’d be frantic work getting ready when one of these sources would come in from Oak Ridge and everything had to be ready to work. And then we would work day and night as the source gradually decayed until it was too weak to use any anymore. And then there would be a period in which we didn’t have to work so hard because we didn’t have the stuff to work with. And always when you’re working on tests, it was even true with Trinity, we worked very hard to get things ready and then we’d sit and wait and wait and wait. That’s the way weapons tests always go.

Kelly: Would you like to comment a little bit about the military’s preoccupation with secrecy?

Diven: Yes. One of the reasons that Los Alamos was started was that the military wanted extreme compartmentalization as far as information was concerned. They didn’t want anybody not working on one phase of the project to know anything about any other phase. 

Oppenheimer felt that that couldn’t work for us—that too much had to be learned too soon. The job here couldn’t be treated in quite that way and be successful.  He insisted that all of the staff members would have access to all of the information, and I think that was a very important part of getting work done on time. But it also meant that we as staff members did not feel any problems of secrecy because we knew all of them.

The only time that would be different was, for instance, in details of how the bomb would be detonated and details of how many bombs we were going to have. Such things as that were kept fairly close, although it was pretty much general knowledge among staff members about how many bombs were going to be coming every month—I mean material to make them. What’s surprising to me, that so many people had the impression that we only had enough material to make three bombs because that’s all that were ever fired during the war, but they were coming at a steady rate and that information is unclassified. I don’t know why there’s so much misconception about it.

Cameraman: Just a second.


Copyright 2012 The Atomic Heritage Foundation. This transcript may not be quoted, reproduced, or redistributed in whole or in part by any means except with the written permission of the Atomic Heritage Foundation.