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Weaponry: Scientists Meet at Berkeley to Lay Foundation to Build an Atomic Bomb

Originally published by World War II magazine. Published Online: June 12, 2006 
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In the summer of 1942, the oily stench of Pearl Harbor still hung on the wind across the United States. Along with the memory of the devastating attack by the Japanese, there was an aura of uncertainty, fear and even despair throughout the country.

Bataan and Corregidor had fallen in the spring, the cruel Death March had begun and Japanese armies had driven Allied forces from most of the Far East. German troops remained unchecked in Europe and North Africa until November, when they were stopped cold at Stalingrad and thrown back at El Alamein. The full import of the U.S. naval victories in the Coral Sea in May and at Midway in June had yet to be understood.

Meanwhile, a group of the world's top physicists was meeting in Berkeley, Calif., to consider developing a dramatic means to end the war. They had come to the University of California at the invitation of their colleague, J. Robert Oppenheimer, to discuss the theoretical basis for the creation of an atomic bomb. When they finished their seminar, the course was fixed for a new age in warfare.

The Berkeley group knew that their counterparts in Germany were also engaged in research that could lead to an atomic bomb. Although little was known at the time about the ultimate effect of such a potent untested weapon, there was no doubt in the minds of most of the physicists who met in California that it would be decisive.

As early as 1939, scientists Leo Szilard and Albert Einstein had urged President Franklin D. Roosevelt to begin government-sponsored research to develop an atomic bomb for the United States. They knew that the German effort, led by their former colleague, the brilliant Nobel laureate Werner Heisenberg, could be formidable. As it turned out, Germany was unsuccessful, perhaps because Heisenberg deliberately slowed down the bomb's development or because Adolf Hitler was more interested in developing rockets than nuclear weapons. But that was in the future, and the only future the physicists in America could see at that point was the mortal danger of a German atomic bomb.

In response to the plea of Einstein and Szilard, FDR initiated a modest program of uranium research. By June 1940, interest in uranium and its properties had increased to the point that the president created a larger organization, the National Defense Research Committee, with a broader scope of activity. He named as director Vannevar Bush, the president of the Carnegie Institution in Washington, D.C. The slowly growing effort gained further impetus in mid-1941 from a startling British document code-named the 'MAUD Report.' Based on British nuclear research, the report stated that a very small amount of uranium-235 could produce an explosion equivalent to that of several thousand tons of TNT. Roosevelt responded by creating a still larger organization, the Office of Scientific Research and Development, which, directed by Bush, would mobilize scientific resources to create an atomic weapon.

Recruitment of scientists intensified. As evidence of Fascist brutality and anti-Semitism had increased in Europe, the pool of physicists in the United States had been augmented by émigrés such as Enrico Fermi, Hans Bethe, John von Neumann, Edward Teller and Eugene Wigner. They, like more than 100 of their counterparts, had fled Europe and the Nazi nightmare for the freedom and security of the United States, and they were eager to join the war effort.

With the U.S. entry into World War II, pressure increased for America to take action. In March 1942, Bush wrote FDR a cautiously worded update on the situation: 'Recent developments indicate…that the [atomic bomb] is more important than I believed when I last spoke to you about it. The stuff [uranium] will apparently be more powerful than we thought, the amount necessary seems to be less, the possibilities of actual production appear more certain.'

Bush went on to say that, while he believed the project would be 'exceedingly difficult,' production could begin on the bomb by the summer of 1943. The president replied: 'I think the whole thing should be pushed not only in regard to development, but also with due regard to time. This is very much of the essence.'

Work on the atomic bomb in the United States now began in earnest. Arthur Holly Compton of the University of Chicago, who was responsible for the design of the weapon, knew the right man to lead that effort to build it. Soon after Bush's March exchange with FDR, Compton asked J. Robert Oppenheimer, then a professor of physics at both the University of California at Berkeley and Cal Tech, to take charge of the initial steps in designing of the bomb. Recalling his response to Compton, Oppenheimer wrote that work on the bomb 'at that time consisted of numerous scattered experimental projects. Although I had no administrative experience and was not an experimental physicist, I felt sufficiently informed and challenged by the problem to be glad to accept.'

Few of his colleagues would have suspected that Oppenheimer had the administrative ability to direct a project of the magnitude that Roosevelt had in mind. He had never served as a department head or a dean. Among his fellow physicists he had the reputation of being otherworldly, perhaps because of his interests in poetry and Eastern philosophy. Some thought that his broad intellectual interests had diluted the kind of intense, focused concentration required for the highest level of scientific endeavor. Although known for his incredible ability to understand the complexities of contemporary physics, he had not done the caliber of original work judged to be Nobel material. In fact, he would never win the Nobel Prize. Yet Oppenheimer would confound his critics and meet the greatest technical challenge of his era.

Oppenheimer's first step on the long road to the development of 'the gadget,' as it came to be called, that burst over New Mexico's Jornada del Muerto ('Journey of Death,' a stretch of waterless desert) in July 1945, and to the bombs nicknamed Little Boy and Fat Man, which destroyed Hiroshima and Nagasaki that August, was to arrange the Berkeley seminar. He secured two dormer rooms at the top of Le Conte Hall beginning the second week in July 1942, nearly three years to the day before the eventual test of the gadget at the desert site that became known as Trinity. Oppenheimer referred to the study group as 'our galaxy of luminaries.'

One of the luminaries was Robert Serber, a colleague and close friend of Oppenheimer's who the following year at the Los Alamos, N.M., research site would reprise the Berkeley seminar in five introductory lectures to the first scientists to join the laboratory. The notes for the lectures, collected as The Los Alamos Primer, would later be required reading for incoming scientists on the project. According to Serber, 'The purpose of the 1942 summer conference at Berkeley was to discuss the whole state of the theory, to make an independent assessment of whether the bomb was a reasonable possibility, and to assess how well everything was known.'

Oppenheimer's gathering resembled in microcosm the massive organization of scientific genius that he directed at the laboratory a year later. While different Berkeley attendees would be assigned specific problems or tasks, they also enjoyed a freewheeling exchange of thought and debate. Barriers to communication were anathema to Oppenheimer and his contemporaries. They believed passionately in the uninterrupted flow of ideas and information among individuals and institutions as well as nations. That tenet had been one of the prime reasons for the dramatic advancement of modern physics. It also accounted for the reason the luminaries feared Heisenberg and his colleagues in Germany. They knew what Heisenberg knew.

The Berkeley attendees could not anticipate that they would, with relative ease, reach consensus regarding their understanding of the immediate theoretical problems of the atomic bomb–but they would be swept on, principally at the instigation of Edward Teller, to consider an entirely different magnitude of weapon, the super, or hydrogen, bomb. The means to conclude World War II were theoretically settled in the dormer of Le Conte Hall in the summer of 1942. The means to conclude everything began to take shape there as well.

Besides Oppenheimer, Serber and Teller, the principals at the summer session at Berkeley were Hans Bethe, Felix Bloch, Stanley Frankel, Emil Konopinski, Richard Tolman and John H. Van Vleck. Bethe, Bloch and Van Vleck would later win the Nobel Prize. All were young men of extraordinary intelligence and talent whose capacity for creative imaging of the physical universe was as great as could be found in any group at that time. During the conference they enjoyed what may have been among the few halcyon days of the entire Manhattan Project.

Robert Serber later reflected on the Berkeley participants' confidence, if not nonchalance, as they entered the meeting. 'By summer [1942] things were pretty well in hand,' he wrote. 'The uncertainties were in the experimental figures, the cross sections, the number of neutrons per fission and whatnot. But they didn't seem large enough to make a difference between failure and success. They might determine whether the bomb would be a little bigger or a little smaller. I think we were lucky that some of the answers came out within ten percent of the final ones.'

At ease or not, they had much to do, for they were now at a stage of development where they needed to nail down some theoretical certainty. Until then, bomb research had been done by small contractors working on discreet problems at various locations around the country, and by the British. Oppenheimer distributed the reports from these varied sources to his Berkeley group and, for the first time in the bomb's development, a panel of experts reviewed the collected wisdom. The task now was to understand the problem as a whole.

The first order of business was the nuclear physics of the so-called gun-method bomb. The gun method bomb, the type that would be used at Hiroshima, was a less complicated technical problem than the implosion method bombs used in the test at Trinity and for the attack on Nagasaki. Principally because it seemed the easiest to do at the time, the gun method was the choice for setting off the uranium-235 core, which, in mid-1942, figured to be the energy source for the weapon. The gun method fired a U-235 bullet at another U-235 mass, neither of which by itself was large enough to sustain a chain reaction but which in combination instantaneously created a 'critical assembly' that released the bomb's explosive energy.

Separation of the U-235 isotope was painfully slow and expensive–less than 1 percent of mined uranium is U-235. An enormous facility at Oak Ridge, Tenn., was created for the separation process. Late in 1942, however, Enrico Fermi and his team produced the first controlled chain reaction, making it possible to produce plutonium, an even more potent source of explosive energy, which was now easier to obtain than U-235.

A new method was required to release the plutonium's energy, however, because plutonium had to be brought to the explosion point much faster than could be achieved by the gun method. A gun projectile would have to travel at what were judged unattainable velocities to initiate the plutonium reaction. The solution was the implosion method, in which shock waves from detonated explosives surrounding the plutonium core converge, crushing the core to critical mass and resulting in explosion.

Credit for inventing the implosion method is usually given to Seth Neddermeyer, an experimental physicist who had been Oppenheimer's student at Cal Tech. Doubtless Neddermeyer's role was critical in bringing implosion to its final realization at Los Alamos, but Robert Serber has pointed out that the idea actually originated with Richard Tolman during the 1942 meeting at Berkeley. 'Tolman came to me one day,' Serber wrote, 'and talked about implosion….We discussed it that summer and wrote a memorandum on the subject….So the story of Seth Neddermeyer the lone genius coming up with implosion on his own is all hokum.' In fact, The Los Alamos Primer includes a crude drawing and some comments suggesting an implosion theory.

Because of the comparative ease and economy with which plutonium could be obtained, and because implosion assured a more compact and reliable bomb, they became the preferred energy source and method of explosion for atomic weapons. The U-235 gun-method bomb was used only once, at Hiroshima. It was, however, the most important practical weapons concept in the U.S. arsenal in 1942. Little Boy would be its name in 1945.

Among other things, the Berkeley participants wanted to determine the yield of an atomic weapon. How much explosive force could be expected from the gadget they were contemplating? What might be its effects? Could they validate the findings of the British MAUD Report?

They had few practical examples to use as comparisons. TNT, Alfred Nobel's invention, was the benchmark. The one great disaster with TNT for which the Berkeley group had some data was the explosion of an ammunition ship in the harbor of Halifax, Nova Scotia, in 1917. Five hundred tons of TNT had flattened 21ž2 square miles of Halifax, killing upward of 1,600 people. Based on the Halifax explosion, Oppenheimer's seminarians extrapolated for their nuclear weapon estimates of explosive force several thousand times that of TNT, and they added newcomers to the tally of explosive destructiveness–the effects of neutron and gamma-ray bursts.

As for the guts of the bomb, the scientists postulated an 8-inch-thick core of fissionable material encased in a heavy metal shell that would hold together long enough (roughly a splice of a millisecond) to reflect back upon the disintegrating core the neutrons set free from the initial fission, thus furthering the chain reaction. Assembly, the cataclysmic joining in the gun bomb of the two fissionable masses, and detonation would take place in so narrow a nick of time that it could not be measured. Just as rapidly, the core would transmute from metal to liquid to gas, fissioning and producing increasing amounts of energy all the while.

Oppenheimer wondered how much fission would result in these conditions. Hans Bethe, who four years earlier had described how the sun and stars generate energy (for which he would eventually receive the Nobel Prize), could make a rough estimate. What, after all, were they dealing with but a very small star?

As the group worked on through the summer, their vision of the task ahead sharpened. Oppenheimer, who was daily becoming more accustomed to his new role, also saw what was needed. He was convinced after the Berkeley meeting 'that a major change was called for in the work on the bomb itself. We needed a central laboratory devoted wholly to this purpose, where people could talk freely with each other, where theoretical ideas and experimental findings could affect each other, where the waste and frustration and error of the many compartmentalized studies could be eliminated, where we could begin to come to grips with chemical, metallurgical, engineering, and ordnance problems that had so far received no consideration. We therefore sought to establish this laboratory for a direct attack on all the problems inherent in the most rapid possible development and production of atomic bombs.'

Before Oppenheimer articulated his vision, however, the Hungarian emigré Edward Teller spoke up, and the discussion veered to another type of weapon. Teller, who is often called the 'Father of the Hydrogen Bomb,' was not the first to conceive of the super bomb, as it was called. Nor was his design of the thermonuclear device the one that was ultimately used. There is no denying his scientific contribution to the super bomb was indeed fundamental and of great importance, but his most critical role in its genesis was that he championed its development with more energy and force than anyone else. Once he came to the conclusion that a thermonuclear weapon could be made, it became his life's quest.

Earlier in 1942, Teller's imagination had been stimulated while he was working with Enrico Fermi at Columbia University on fission problems associated with nuclear bombs. In Teller's words, when he and Fermi were walking back to the laboratory after lunch one afternoon, 'Fermi posed the question: 'Now that we have a good prospect of developing an atomic bomb, couldn't such an explosion be used to start something similar to the reactions on the sun?" First they would split a heavier nucleus–fission–to create an explosion that would generate enough energy to fuse lighter nuclei into a still lighter element–fusion–and produce an even more powerful result. [In the case of a hydrogen bomb, the conversion of mass to energy increases seven-fold from fission to fusion.]

'The problem interested me,' said Teller. He followed Fermi's offhand speculation with a thorough study and decided that it could not be done. Then, a few weeks later, he rekindled the fire with the help of fellow theorist Emil Konopinski at the Manhattan Project laboratory at the University of Chicago.

Teller and Konopinski were only temporarily at Chicago while they waited for the Berkeley study group to assemble, but as Teller put it: 'I decided that our best contribution to that study might be a detailed review of the reasons why deuterium [an isotope of hydrogen] could not be ignited by an atomic bomb. Konopinski agreed, and we tackled the job of writing a report to show, once and for all, that it could not be done. We wanted no one else to waste valuable time investigating Fermi's curbstone suggestion.' The result of Teller and Konopinski's work was a reversal of Teller's stated expectations. They concluded that 'heavy hydrogen actually could be ignited by an atomic bomb to produce an explosion of tremendous magnitude.'

The two scientists took their calculations with them to the study group at Berkeley. The Berkeley agenda, however, was shaped and driven by the urgency to come up with a weapon whose development lay within the realm of what was practical. As the slogan went those days, 'There's a war on.' But almost immediately on arrival Teller raised the question of developing the fusion bomb, although the details regarding even the fission bomb were not yet clear.

As Hans Bethe recalled: 'Some members of our group, under the leadership of Serber, did calculations on the actual subject of our study, the neutron diffusion in an atomic bomb and the energy yield obtainable from it. The rest of us, especially Teller, Oppenheimer and I, indulged ourselves in a far-off project–namely, the question of whether and how an atomic bomb could be used to trigger an H-bomb. Grim as the subject was, it was a most interesting enterprise. We were forever inventing new tricks, finding ways to calculate, and rejecting most of the tricks on the basis of the calculations. It was one of the best scientific collaborations I have ever experienced.'

Serber saw it somewhat differently. He wrote: 'The discussion that summer wasn't confined to fission. We reviewed the theory, but everyone seemed to be saying, well, that's all settled, let's talk about something interesting. Edward Teller is a disaster to any organization….Edward was always full of ideas….But the main thing [he] was hooked on, of course, was the idea of pushing through to a thermonuclear weapon, an H-bomb….He'd come in every morning with an agenda, with some bright idea, and then overnight Bethe would prove that it was cockeyed. They implicitly assumed that I had the fission bomb under control, that there was nothing to worry about….It was a lot of fun, very lively….'

One of Teller's bright ideas was also very frightening. Late in the conference, he arrived one day with calculations suggesting the possibility that the fission reaction in the atomic bomb might generate enough heat not merely to trigger the super bomb but to set the earth's atmosphere afire. The idea of an atomic chain reaction run amok was not new. Ernest Rutherford, who posited the structure of the atom, had suggested in 1903 that it was conceivable that 'a wave of atomic disintegration' might be initiated that would destroy the planet. Others, notably Leo Szilard and George Gamow, had analyzed the problem at length in the 1930s. No one had come up with a definitive answer to this unnerving theoretical question. But now the means were at hand to prove or disprove the theory.

Oppenheimer immediately called an intermission in the proceedings while the scientists evaluated Teller's speculation. Serber treated the matter lightly, saying that 'Bethe went off in his usual way, put in the numbers, and showed it couldn't happen. It was a question that had to be answered, but it never was anything, it was a question only for a few hours.'

Bethe was less sanguine. He later recalled: '…[We] made some very quick estimates which showed that [igniting the atmosphere] was essentially impossible….[We] thought that it was so drastic a possibility that we shouldn't rely on our physical intuition or on the few formulae which we wrote down in one day on a few pieces of paper.'

In fact, the question was continuously investigated by Bethe, Teller, Konopinski and others until the shot at Trinity Site in July 1945 proved the conflagration would not happen. Even at Trinity some scientists were still fearful of the results.

Bethe's initial calculations held up. What they showed, as he wrote later about the hydrogen bomb, was that igniting the atmosphere could not occur 'because…the small mass of the bomb…would heat only a small volume of the earth or its atmosphere, and even if nuclear reactions were started, radiation would carry away the nuclear energy much faster than it developed, and the temperature would drop rapidly so that the nuclear reaction would soon stop.'

But Oppenheimer did not know that in the summer of 1942. Despite his confidence in Bethe and the others, he felt compelled to notify his boss, Arthur Compton. It is a measure of how seriously Oppenheimer took the situation that he traveled from Berkeley to meet Compton at his summer cottage on a lake in southwestern Michigan. There they discussed the theoretical possibility of the end of the world. After hearing Oppenheimer out, Compton made a momentous decision: The project would have to cease if the scientists could not be sure that the earth would not be destroyed. 'Better to be a slave under the Nazi heel,' he said, 'than to draw down the final curtain on humanity.'

With that ominous possibility in mind, Oppenheimer returned to Berkeley. But the steady Bethe had done his calculations, and the question was soon settled to the extent that the scientists felt it was safe to resume the work. Oppenheimer agreed. He reassured Compton, and the project continued. The seminar's original purpose regained primacy, and the luminaries concluded that development of an atomic bomb was possible.

Intellectual give-and-take is the fuel for the engine of scientific work. It steadily propels any enterprise with energy such that–excepting the rare breakthrough vision of a Sir Isaac Newton or an Einstein–results in incremental advances. Fortunately, the diversion created by consideration of the super bomb did not delay to any significant degree the Berkeley study group's achieving a working understanding of the atomic bomb. That was the critical thing for that time.

The diversion did not die, however. It caused serious problems at Los Alamos later in the development of the weapon that in turn contributed to a breach between Teller and Oppenheimer. That disagreement had grave consequences for Oppenheimer, culminating in Teller's testifying against him at his 1954 security hearing. Those hearings finished Oppenheimer as a contributor to the debate on the future of atomic energy.

Development began in earnest a few months after the scientists left their Berkeley seminar. By April 1943, most of them had traveled to the mesa at Los Alamos and were engaged in what Oppenheimer called 'an unparalleled opportunity to bring to bear the basic knowledge and art of science for the benefit of [the] country. Almost everyone knew that this job, if it were achieved, would be part of history.'

More than just becoming a part of history, the project changed the course of history. A comment made by Hans Bethe after the bomb became a reality sums up the weapon's significance to mankind. 'Life,' he wrote,'soon became more serious.'



This article was written by Robert LaRue and originally appeared in the May 2000 issue of World War II magazine.

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One Response to “Weaponry: Scientists Meet at Berkeley to Lay Foundation to Build an Atomic Bomb”


  1. 1
    Clayton says:

    thus is stupid



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