Tom Hull: Jeremy Bernstein: Nuclear Weapons

One of the first things that Oppenheimer asked Serber to do was to give a series of lectures -- in the event there were five -- that would serve as an introduction to the physics of the bomb for new arrivals. It is worth commenting on this. First of all, from a fundamental point of view there was no new physics required to make a bomb. The Los Alamos physicists often said that when they came back from the war they found the same set of problems on their desks that they had left. However, building nuclear weapons required using what was then standard physics in novel ways. This is what Serber explained in his lectures. The lectures were attended by some fifty people and were taken down by the well-known physicist E. U. Condon. Afterward, he and Serber wrote up the notes. They were of course classified. They became declassified in 1965 and were published in book form with Serber's commentaries in 1992.

No doubt because of the secrecy, physicists who had not been involved with the bomb knew very little about it. And even the physicists who did know weren't talking. When I was an undergraduate at Harvard in the late 1940s many of my teachers had been involved. John Van Vleck, who had been Serber's Ph.D. advisor at Wisconsin and then had gone to Harvard, was one of the people who attended the 1942 conference that Oppenheimer organized in Berkeley. Kenneth Bainbridge, who was for a while chairman of the department, had chosen the test site for the first atomic bomb explosion in Almogordo, New Mexico. Norman Ramsey, from whom I took a course, had supervised the armoring of the Hiroshima bomb on Tinian Island in the South Pacific. Roy Glauber, who was just starting his academic career -- he shared the Nobel Prize in Physics for 2005 -- went to Los Alamos immediately after finishing the course work for his bachelor's degree. And the president of the university, James Conant, had been one of the original civilian leaders of the program. Despite all of this, I do not remember a single part of any course in which the physics of nuclear weapons was discussed. I do not even remember any of these people mentioning any of this in any context. I can understand this at the time. The war had been over for only a very few years and the Cold War was just beginning. However, not long ago I decided to make a little survey. I went to a physics library and looked at every textbook of nuclear physics I could find. There was not a single one of them that explained how to find the critical mass of a uranium sphere. Most of them did not even explain what a critical mass was. This disturbed me, especially in view of what seemed to be happening in the world.

(pp. 169-170):

Smoky and Galileo were part of the longest and most extensive test series ever done at Mercury. It was called "Operation Plumbbob." It consisted of twenty-nine detonations, beginning with Boltzmann on the 28th of May and ending with Morgan on the 7th of October. Some of the tests were on towers, others from balloons, one in a shaft, and another in a tunnel. In a "boys will be boys" gesture the one in the shaft had an odd twist that resembled what we used to do with firecrackers when we were kids. We'd put them in a tin can to see what happened when they went off. Here the grown-up boys put a lid on the shaft to see what would happen. They figured that so much energy would be imparted to the lid that it would reach a velocity greater than that needed to escape the gravitation of the Earth. It would become, before Sputnik, the first space vehicle. It is not likely that this happened, but the lid was never found after the explosion. The Plumbbob explosions ranged in yield from half a ton -- Lassen -- to seventy-four kilotons -- Hood. They released 58,300 kilocuries of radio iodine into the atmosphere. A "curie" is a unit of radioactive disintegration that is equivalent to thirty-seven billion decays of anything per second. To get some idea of scale, one thousandth of a curie is about what would be used in a liver scan. The amount of radio iodine that Plumbbob put into the atmosphere was estimated to have caused an additional 38,000 cases of thyroid cancer, leading to some 2,000 deaths. Most of this radiation was deposited in the northeastern, far western, and midwestern states. There was a cluster in Maine. But this is not the only thing that made the Plumbbob tests notorious. The Department of Defense decided that this would be a splendid opportunity to study the reactions of soldiers and marines to atomic warfare. During the series some 18,000 servicemen participated. Because the tests were frequently postponed they were able to make substantial contributions to the Las Vegas economy at all levels. At Smoky, some three thousand soldiers were brought close to ground zero not long after the explosion. They had watched the explosion from trenches about a mile away. This explained the sound of helicopters that I had heard that morning. It is difficult to imagine now that our defense establishment would have done something so absurd. But there it was. The health of the Smoky soldiers was followed for several decades. In 1980, a survey showed that their leukemia rates were elevated. Four would have been a baseline number of cases expected in the general population, whereas there were ten.

(p. 178):

Not to be outdone, in 1962, Los Alamos supplied a hydrogen bomb to be detonated in outer space. As we will see in the next chapter, such weapons have yields equivalent to millions of tons -- megatons -- of TNT. The Los Alamos bomb was put on a Thor rocket and launched on July 9th above Johnson Island in the Pacific -- project Starfish. It exploded at an altitude of 250 miles with a yield of 1.4 megatons. The result was more than was bargained for. An electron belt was temporarily created that managed to destroy seven satellites, including the first commercial communications satellite.

(p. 211):

Oppenheimer, who was busy beyond human endurance, had to spend time every week with Teller, listening to his latest failed ideas for making the super. I have never really understood Teller's obsession. Why were fission bombs not enough for him? Was it the intellectual challenge? Was he worried that the Russians would get there first, although this was probably not a consideration during the war? Was he angry that Oppenheimer had made Bethe head of the theory division instead of him and he wanted to carve out a new domain? A combination>? I don't know. I have asked myself what would have happened if, at Nagasaki, we had dropped a twenty-megaton hydrogen bomb instead of a twenty-kiloton fission bomb. The fission bomb killed 75,000 people and devastated everything within a radius of one mile from ground zero. A twenty-megaton bomb would have inflicted third-degree burns on everyone within a distance of twenty miles and would have devastated everything up to a distance of fourteen miles. Would the Japanese have surrendered sooner? Nagasaki was bombed on August 9th and the Emperor surrendered on the 14th. What would a hydrogen bomb have accomplished? In the years following the war, Oppenheimer often said that the problem with the hydrogen bomb was that the targets were too small.

(pp. 213-214):

While Teller and his group were knocking their heads together trying to make the classical super work, there was another activity going on that did not seem to attract much attention. This was the work of Klaus Fuchs and von Neumann. Klaus Fuchs, of whom we will hear much more in the next chapter, came to Los Alamos as part of the British delegation in August 1944. He had already been working on aspects of the bomb in England and soon proved himself to be an invaluable member of Bethe's theoretical division. He was known to have a photographic memory and to have involved himself in all aspects of the program. Almost no one was better informed. He was also a Russian spy -- surely one of the most successful that has ever lived. By the fall of 1945, he had turned over to the Russians what amounted to a detailed blueprint of the gadget, whose test he had witnessed. The Russian physicists were ordered to duplicate the gadget, which they did. It was successfully tested in August 1949. Considering the effort the Russians put in and the ability of their scientists, it is certain that they would have gotten the bomb sooner or later. Fuchs probably saved them a couple of years. But, in 1946, Fuchs had turned his attention to the super. He and von Neumann patented their work and, as far as I can tell, the patent is still classified. However, in the spring of 1948, Fuchs turned it over to the Russians. Some of what he turned over has found its way back here by the back door, so to speak. In particular there is a diagram that has now been widely circulated. Much of this diagram is of no interest because it is connected to the classical super. But a part of the diagram is of great interest because it is the first inkling of how to make a hydrogen bomb. After Fuchs was exposed as a spy, both Bethe and Oppenheimer belittled anything that Fuchs could have told the Russians about the hydrogen bomb. They even said that they hoped the Russians would use Fuchs as a guide because that would lead them down a blind alley. I have often wondered if they actually knew what Fuchs turned over and, if they had seen this diagram, whether they still would have been quite so cavalier.

(pp. 222-223):

Finally, I want to discuss the question of whether the hydrogen bomb should ever have been built in the first place. Let us recall the events that led up to President Turman's decision. In August 1949, the Russians successfully tested their first fission bomb. On January 27, 1950, Fuchs confessed to his espionage. In October 1949, there was a four-day meeting of the General Advisory Committee of the Atomic Energy Commission. This committee consisted of the highest-level people in the weapons program. Rabi and Fermi were members, as was Conant. Oppenheimer was chairman. The committee decided for various reasons that there should not be a crash program to build the hydrogen bomb and, above all, not one that was publicly announced. Some members of the committee thought that the hydrogen bomb was not a weapon of war but a method of genocide. Rabi and Fermi thought there should be a conference with the Russians to seek an agreement not to build it. If that failed, nothing would have been lost because, at the time, no one had a clear idea of how to build one anyway. But, after Fuchs's confession, the pressure on Truman to do something was irresistible, and four days later he publicly announced a crash program to build the hydrogen bomb. The predictable happened -- a hydrogen bomb race. The Russians exploded theirs in 1952, the British in 1955, the Chinese in 1967, and the French in 1968. Probably every country that has atomic weapons is engaged in building the hydrogen bomb. There is some sad irony in all of this. In the same 1952 Ivy series there was a test called Ivy King. This was a pure fission bomb -- no boosting -- that had been designed by Theodore Taylor of Los Alamos. It produced a 500-kiloton yield. Now here is the irony. In recent years the Russian and American nuclear strategists have concluded that megaton bombs are unnecessary. The arsenals have been cut back to bombs of several hundred kilotons. Put another way, if the hydrogen bomb had never been built and pure fission bombs had continued to be developed, then the Russian and American nuclear arsenals would look about the same as they do now.

posted 2008-06-28