Hiroshima: Memoir of a Bomb Maker ... "The Gadget"





Editor's Note: The late Paul Olum, who later served as president of the University of Oregon, worked in his youth on the atomic bomb at Los Alamos. Following is a selection from a manuscript he left behind. It has never before been published. It was made available to HNN by George Beres, who served with him on the University of Oregon Arms Control Forum. The memoir was written in 1983 following a reunion of Los Alamos scientists. It is reprinted with permission of the Olum family.

The Los Alamos Scientific Laboratory opened in April, 1943. Its charge was straightforward, but quite unlike anything before in history: to do the basic scientific and technical research necessary to determine whether a nuclear bomb could be constructed; and, if that appeared feasible, to build such bombs when the material for them became available. I joined the project as part of the theoretical physics group roughly a month before actual opening of the laboratory.

My wife, Vivian, and I had driven from Princeton, where I was part of the Manhattan Project working on the separation of Uranium 235, a rare isotope of uranium which was the material needed for a fission bomb. When the decision was made to open a laboratory for the actual purpose of building the bomb, the Princeton project was closed, and most of us involved in it were invited to Los Alamos.

I was young, 24, and still a graduate student at Princeton University in theoretical physics and mathematics. A very large share of the people there were quite young, in their 20s, even senior group leaders on the project like Richard Feynman and Robert Wilson; and many of the others were people in their 30s. Robert Oppenheimer, the Director, was relatively old for the group, in his late 30s.

The most unbelievable, most extraordinary scientific community ever collected in the world.

Los Alamos was an extraordinary place. It is in an isolated area of New Mexico, some distance north of Santa Fe, up on a mesa. The whole area was fenced in, and there were military guards and strict security at the gates. There was no way to get in or out without passing through these security checks.

We weren't even allowed to tell our parents and friends where we were going. All we could say was that we were somewhere in the continental United States, the actual location a secret. Our parents wrote to us by writing to Princeton; one person collected the mail there and forwarded it to an appropriate place in Santa Fe from which the mail was gotten to us. Later, they could write to Santa Fe. All mail, incoming and outgoing, was censored, the only place within the United States where such censorship took place.

The strict security had an important scientific purpose, namely that by restricting totally, at least in principle, all communication with the outside world, it was possible to have a completely free flow of information among the scientific staff inside the laboratory. Oppenheimer insisted on that, and it was important evidence of the strength of his leadership that he could pull it off, because the military and, in particular, Gen. Groves, head of the Manhattan Project, could hardly stand the notion that everyone on the scientific staff could talk to everyone else, and discuss what they were doing. This was not the Army's way of running a secret project. However, it was extraordinarily important that we were able to do so because out of such interchanges and out of all our open seminars and conferences came the creative new ideas which made success ultimately possible. The result is that all of us knew just what was going on and what we all were doing. From the beginning, we knew we were building a bomb which could destroy a whole city, could kill hundreds of thousands of people. We also knew that what we were building was unquestionably the most elementary, pre-model-T version of such a bomb, and that others more powerful surely would follow. We sat in meetings discussing how to maximize the deadly destructive power of this weapon. We knew then, when we stopped to think about it, what a terrible thing we were engaged in.

We never called it a bomb, lest somehow the word should slip out in some unauthorized place. It was always referred to as"the gadget."

At the same time, all of these young people found themselves in the most unbelievable, most extraordinary scientific community ever collected in the world, except perhaps for brief international conferences lasting a few days. Some of the greatest names in physics were there: Enrico Fermi from Italy, Niels Bohr from Denmark, together with his son Aage; Hans Bethe, I.I. Rabi, Richard Feynman, Owen Chamberlain, Emilio Segre, Ed McMillan. Every one of these people is a Nobel laureate. In addition, there were Oppenheimer himself, Edward Teller, Rulolph Peierls from England, the famous chemist Kistiakowski from Harvard, Victory Weisskopf, a great physicist from MIT. Johnny von Neuman, who was probably the leading mathematician of his day, the world's best, came and went from time to time, but spent a good deal of his time at Los Alamos. And there were a great many more, mostly younger scientists.

To be in the company of these people, many of the world's greatest minds, was an incredible experience one never could have found anywhere else. Inevitably, we talked from time to time about other things than the atomic bomb: about the world of science and about new ideas and new ways of looking at things. I learned to ski at Los Alamos, taught by European scientists, and we went out and climbed in the mountains on skis and talked a great deal, mostly about science. It was, in retrospect, a strange world: an unbelievably wonderful experience set in a truly terrible endeavor. At the beginning, shortly before the project opened, there were relatively few of us on the scientific staff there, perhaps 50 or so. But the numbers grew and continued to grow as the problems became more complex. We were divided into many research groups: experimental physics, chemistry, ordinance working on high explosives for rapid assembly of the completed bomb, theoretical physics such as the one I belonged to.

There were problems that had to be solved. For example, after one neutron split a uranium atom, how many neutrons would be produced from the split? To have an exponentially multiplying chain reaction, it was necessary that something like two or more neutrons would be produced on the average from each fission. The experiments showed there were.

Another very important experiment was done by the cyclotron group. They showed that neutrons came out extremely fast after fission took place. That was crucial, because if the neutrons had come out slowly, and slowly means even one-hundred-thousandth of a second after fission, the bomb would not have worked. It would have blown itself up before the chain reaction had time to proceed very far.

Many other problems had to be solved before it was possible to know whether or not such a bomb could be built. Incidentally, we never called it a bomb, lest somehow the word should slip out in some unauthorized place. It was always referred to as"the gadget." A crucial part of our problem was that there was no way to test this gadget in advance, or to test the functioning of parts of it. We had to do all of our experimental and theoretical planning on the basis of information at the atomic level, and could not know whether it would really work until it was all done and built.

My own work was in the group with Victor (Vicky) Weisskopf. I really was sort of a research associate to Vicky, very much the way a research associate does in the laboratory, working with a senior professor. We worked closely together. He would walk around with his head full of ideas and plans, and we would talk about them. I would make suggestions and work on details, then talk some more with him. It was a wonderful experience for me because Vicky was a great physicist and an extremely warm human being. In the earliest days, my work was on determining how the neutrons moved around inside the gadget and struck their targets. Later, I worked on the solution of a very complex differential equation whose purpose was to predict the total energy released by the bomb.

All of the time we were doing these things at Los Alamos, the fissionable material was being produced a tiny bit at a time at the huge plants at Oakridge and Hanford. At Oakridge, they were separating the Uranium 235 needed for a uranium bomb. At Hanford, they were creating from large nuclear piles the new Element 94, plutonium, which also underwent fission. Finally, by the middle of 1945, the fissionable material became available. In the meantime at Los Alamos, the research was being completed and plans made. The critical size was determined, and the difficult process of assembling a bomb was resolved. Assembly could be done one of two ways, either by putting one half in the mouth of a cannon and shooting the other half of it, or else by surrounding a sphere of loosely packed material with TNT and"imploding" it (i.e., compressing it very greatly at enormous speed). The latter was more tricky, but it was the only way that would work for plutonium.

Then, on July 16, 1945, at Alamogordo, New Mexico, the bomb test (code named"Trinity") was conducted. It was a plutonium bomb, because the project leaders were so worried about that one that they had to test it to be absolutely sure of it. I saw the test from many miles away, sitting on the side of a hill. The explosion was an incredible thing, and seemed at first to fill the whole of the sky, so that those of us theoretical types who were watching from a distance (being of no use at the actual test) were momentarily afraid that all of our colleagues had been consumed by the blast.

Twenty-one days later, on Aug. 6, 1945, a bomb was dropped on Hiroshima, this time a uranium bomb. Three days later, on Aug. 9, a plutonium bomb was dropped on Nagasaki.

That is a brief history of what happened. Why did we do it, why did we work to produce such a terrible weapon? Most of us were young, decent, moral people who surely did not want to kill anybody. We did not know exactly how many would die, but the fact perhaps 130,000 people died in the Hiroshima explosion was no surprise; that was the right order of magnitude with a bomb going off equivalent to 16-18,000 tons of TNT, maybe a little less. The Nagasaki bomb was somewhat more powerful, but killed fewer people, partly because of geometry of the city.

Why did we let ourselves do such an incredibly awful thing, sitting there in our offices and conference rooms and talking about it, then doing experiments and calculations, moving step-by-step to the creation of this horror? Would I do it again if I had to? Do I feel now that it was a wrong thing to do?

I feel still today that there was no choice. We knew the Germans were working on a nuclear bomb, and that they had started as much as two years earlier than we. We knew it was possible they could get it. We knew if they got it and could deliver it in their huge intercontinental rockets, they could very likely win the war, ultimately taking over the whole world. I felt then there was indeed no choice, knowing that the Germans were doing it, and what consequences would be for all of us if they got a nuclear bomb and we did not.

But that raises another question. When V.E. Day, victory in Europe, came in the spring of 1945, we were quite certain the Japanese had no bomb. The Japanese had hardly gotten anywhere toward building a bomb, and there was no belief they possibly could have one. Why didn't we all stop and walk off the project then? We no longer needed what we had been trying so hard to achieve. We didn't have to worry about somebody else getting it first. Nonetheless, I know of no one, none of the scientists at Los Alamos, none of our friends, who had to make such a decision. I suppose there are many reasons for what it was. Probably the best, and it is not one to be particularly proud of, is that when you are involved in something like that and carry it close to final creation, it just is hard to stop. You are totally caught up in it. You are making a bomb for a military purpose, for a war you are engaged in, and the war still is going on, and you haven't quite finished the job. I think very few of us stopped to think on V. E. Day that the justification we would have given for working on the bomb in the first place was no longer there. One might argue that if it wasn't built then, it would be built later. By April of 1945, it was essentially done, so why not see it through?

But I do think that in the main, it was actually the situation of scientists in the middle of an extraordinary project, unique in the world's history, wanting to see the results of what they had done. But there are other questions. After it was finished and tested at Alamogordo, it was dropped on Hiroshima in Japan. Why wasn't there a demonstration drop? Why drop it on a city and kill all those people? Weren't the Japanese already reeling from the firebomb raids and other attacks, and near defeat? On the question of a demonstration drop, things were a little different. Many scientists thought it was the proper way to go. Many scientists signed petitions urging a demonstration drop somewhere away from any city. Tell the Japanese it was coming, and tell them what it was like. Let their scientists get out their measuring instruments to see what such a bomb would do.

But this proposal was resisted very strongly by many of those in power. Oppenheimer himself was one of the strongest proponents of dropping the bomb on an inhabited city, and that surely was the position of most of the military. Gen. George Marshall had said an invasion of the Japanese Islands would cost somewhere between 500,000 and a million American casualties, possibly even more. The bomb itself might bring the war to an end without an invasion. It might mean killing a great many Japanese, one or two-hundred thousand, but presumably many more of them would die in an invasion. It was, after all, the Japanese who started the war. Under these circumstances, we certainly had no right to say:"Don't drop the bomb. It is a terrible thing, so invade instead." It was the soldiers, not us, who were going to have to invade, and many of them would lose their lives. Beyond that, we were scientists who could work on building the bomb. But we did not fully know the military situation, and whether Japan was about to collapse.

These concerns made the decision to drop the bomb on a city understandable. Nonetheless, I had hoped, as did many of us, that we could at least try a demonstration drop first. If that did not convince the Japanese to surrender, then the bomb could be used against a city. There still would be no invasion.

We had only three bombs to begin with in the summer of 1945: one for the test at Trinity, and two more-- for Hiroshima and Nagasaki. There would have been one or two more in September, perhaps a couple more in October. Then they would have started coming faster and faster. A demonstration drop might have been worth the risk. However, the Hiroshima bomb perhaps really was necessary, with maybe no Japanese surrender without it. Even so, I feel strongly that dropping a bomb on Nagasaki three days after Hiroshima was unconscionable. The Japanese had no time to recover, no time to find out what happened at Hiroshima, which was in shambles, no time to surrender if they had wanted to.

There was no reason on earth why the Americans should not have told the Japanese that we have more of these, and we will give you, say, two weeks, and if you don't surrender after that, we will drop more of them on your cities.

Those were things we all worried about then, and continue to think about today, 40 years after the bombings. But now everything has changed, for the United States possesses today about 12,000 strategic nuclear warheads. We have an equal number of tactical nuclear warheads which could, under appropriate circumstances, also be used for strategic bombing. All of these warheads are hydrogen fusion bombs, enormously more powerful than the uranium and plutonium fission bombs of 1945. Their explosive power varies, some as low as 100,000 tons of TNT equivalent, others as much as a million tons or more. It is worth remembering that the one that demolished Hiroshima represented some 16,000 or so tons of TNT equivalent. The present 12,000 warheads could destroy the Soviet Union 10 or 20 times over. The Soviet Union has 200 cities containing 100,000 or more people. A single one of these warheads could destroy most of those cities. The largest bombs likely could destroy Moscow or Leningrad; surely two or three of them could. Indeed, just one nuclear submarine of our fleet carries 240 nuclear warheads, so that two such American submarines alone could destroy every Soviet Union city larger than 100,000 and a large number of smaller ones, as well.

It is worth noting by comparison that Eugene is about the 250th largest city in the United States, and the Soviets have roughly the same number of warheads as we do. So it would not take much of the Soviet arsenal to make Eugene a reasonable target, Portland a certain one.

Beyond this terrible threat, and even more frightening, are the recent"nuclear winter" studies. A large group of first-rate scientists from a variety of relevant fields have come to the conclusion that even a moderate nuclear attack, involving on the order of a thousand of these powerful nuclear weapons, could cause a huge cloud over the earth, blocking out the sun and creating a"nuclear winter." This inability of the sun to shine through the atmosphere would most probably result in the destruction of all life on earth-- all human beings, all animals and plant life. These are not wild fantasies. They have been carefully researched by people from a number of different disciplines, and all have been published. Donald Kennedy, the president of Stanford University and a famous biologist, is one of the leaders who organized the symposium at which this terrible threat was first presented.

And so we face the possibility of the annihilation of the human race, not just the annihilation of two major countries. We already have weapons that are 10 times or more the amount needed to destroy each other completely. In the face of this, it seems to me crucial to get some kind of arms control agreement that will start reducing this incredible nuclear overkill. I have, therefore, become an ardent advocate of the nuclear freeze. This doesn't mean we should simply freeze everything in place and stop there. If you are on a train hurtling to destruction and you want to turn it around and go the other way, you have to stop it first. A nuclear freeze, if done right in stages, would first freeze all testing of bombs, then all deployment of new weapons, and finally all production of weapons. That would be only the beginning. At that point, one could start on mutual, negotiated reduction of weapons. With the incredible overkill we already possess, I do not believe there is any risk whatever to us in this process. April 15, 1983, was the 40th anniversary of the opening of the Los Alamos Laboratory, and a reunion was held. The relatively few people who were there in the very earliest Manhattan Project days, about 100 or so, were invited back for this reunion.

My wife and I talked about it. We found it hard to go back to a reunion of old friends to" celebrate" the building of a bomb that then led to the hydrogen bomb and to where we are today. What I did was call a number of friends and scientists from the days of Los Alamos whom I admired the most, leading scientists such as Bethe, Weisskopf and Wilson. I said to them,"We can't possibly go back to Los Alamos just to celebrate. We've got to do something."

The response was one you always get in such a situation. They said,"You're absolutely right; why don't you do something, and we'll support it." I said I would, and, with my wife's help, drafted a petition. It is a statement on the part of the Los Alamos scientists who began the project, calling for an end to the nuclear arms race and a mutually agreed upon reduction of nuclear armaments.

I took it with me to Los Alamos, but the directors of the laboratory would not even let me announce from the podium that I had a petition for people to sign. So some friends and I handed it around personally during the reunion and at the final banquet.

It was signed by 70, most of the leading scientists who were at Los Alamos in the early days and who had come to the reunion; but not by all of them. Five of the signers are Nobel Prize winners, and many others are leaders in the field of science today. I won't quote here the entire petition. But one sentence from it indicates the depth of our feeling:

"We are appalled at the present level of the nuclear armaments of the nations of the world, and we are profoundly frightened for the future of humanity."

(c) George Beres


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