Inside the Centre: The Life of J. Robert Oppenheimer (66 page)

Condon thought this was ridiculous and fundamentally incompatible with the successful pursuit of science. The issue came to a head towards the end of April, just six weeks after Oppenheimer and Condon had moved to Los Alamos, when Oppenheimer flew to Chicago to discuss the
schedule for plutonium production with Arthur Compton. Groves was furious and, on Oppenheimer’s return, stormed into Oppenheimer’s office to make his feelings known to both Oppenheimer and Condon. Condon stood up to Groves and defended this breach of compartmentalisation, but was puzzled to see that Oppenheimer was not supporting him. A few days later, Condon resigned, giving his reasons in a long letter to Oppenheimer. ‘The thing that upsets me most,’ he told Oppenheimer, ‘is the extraordinary close security policy.’

He was, he said, ‘so shocked that I could hardly believe my ears’ when Groves reproached them for discussing technical questions with Compton: ‘I feel so strongly that this policy puts you in the position of trying to do an extremely difficult job with three hands tied behind your back that I cannot accept the view that such internal compartmentalization of the larger project is proper.’

So alien did this way of thinking strike Groves that he was convinced Condon had kept the real reason for his resignation quiet. ‘The considerations he cited in his letter of resignation,’ Groves said of Condon, ‘did not seem to justify his departure.’ His own impression, he went on, was that Condon was ‘motivated primarily by a feeling that the work in which we were engaged would not be successful, that the Manhattan Project was going to fail, and that he did not want to be connected with it’. As far as I am aware, there is no evidence in anything Condon wrote or said to support Groves’s interpretation of his reasons for leaving the project.

During his brief time at Los Alamos, Condon made at least one important and lasting contribution, not only to the work of the laboratory, but also to the physics of atomic-bomb manufacture, and that was his writing up and editing of Robert Serber’s introductory lectures, which formed
The Los Alamos Primer
(the title was Condon’s), a copy of which was given to every scientist on their arrival. There are several references among the memoirs and histories of Los Alamos to the fact that Serber was not a particularly good lecturer, but in print the lectures present a masterfully lucid account of bomb physics, some of the credit for which must go to Condon.

There were five lectures, the first of which was given on 5 April 1943, and the last on 14 April. The first lecture begins with the admirably clear and forthright statement: ‘The object of the project is to produce a
practical military weapon
in the form of a bomb in which the energy is released by a fast-neutron chain reaction in one or more of the materials known to show nuclear fission.’ Actually, from a security point of view, in its use of the word ‘bomb’, this statement was a little
too
clear. ‘After a couple of minutes,’ Serber later recalled, ‘Oppie sent John Manley up to tell me not to use that word. Too many workmen around, Manley said. They were worried about security. I should use “gadget” instead.’ The word ‘gadget’ stuck and became the one everyone at Los Almos used to refer to the thing they were designing and manufacturing.

After spelling out the purpose of the project, Serber’s lectures go on to summarise the current state of knowledge regarding all aspects of bomb physics, much of which had remained unpublished and was therefore news to anyone not previously involved in the atomic-bomb project. He begins with a discussion of the fission process itself, emphasising that the energy release in fission is, per atom, more than
ten million times
that of an ordinary combustion process, such as that of a fire or a chemical explosion. Serber then explains the phenomenon of a chain reaction and says that it would take eighty generations of reactions to fission one kilogram of U-235. Those eighty generations would take place in 0.8 microseconds (a microsecond being one-millionth of a second), producing an explosion equivalent to 20,000 tons of TNT.

The lectures next provide a summary of what was then known about the physics and chemistry of the relevant materials, U-238, U-235 and Pu-239, and explain how plutonium is produced from uranium by a series of nuclear reactions. The calculations required to estimate critical mass are given and explained, and are used to provide a basic figure of 200 kilograms for U-235, which, Serber explains, ‘more exact diffusion theory’ developed at Berkeley in the summer of 1942 brought down to 60 kilograms. When a tamper is used to reflect back neutrons that would otherwise escape, Serber goes on, the critical mass for U-235 would possibly be as low as 15 kilograms, and for Pu-239 lower still. But, he was at pains to emphasise, all this was, in the spring of 1943, theoretical and uncertain. A large part of the task facing the laboratory was to provide experimental data upon which more reliable and accurate calculations could be made:

In a section headed ‘Damage’, Serber demonstrated just how much scientists already knew about the devastation that an atomic bomb would cause. ‘Several kinds of damage will be caused by the bomb,’ he stated. First, there would be the damage from neutron radiation, which he estimated to be effective within 1,000 yards of the explosion. In notes that Serber added in 1992
^fn48
to the published version of
The Los Alamos Primer
, he says that in 1943 he had ‘overlooked a more serious source of lethal radiation’, namely the release of extremely energetic gamma radiation, the range of which, for the Hiroshima bomb, was 4,000 feet. Second, there is the damage caused by the blast or shock wave. Serber estimates that a bomb equivalent to 100,000 tons of TNT would have a destructive radius of about two miles. Other topics covered by his introductory lectures included the efficiency of the explosion (the proportion of the material that is actually fissioned before it all expands and blows apart), the possible methods of detonation and the various techniques of assembly.

The very last thing Serber dealt with in these lectures, under the heading ‘Shooting’, was the question of how the bomb was to be ‘fired’ – how, that is, the subcritical pieces of fissionable material (uranium or plutonium) were to be brought together to form a supercritical mass. The first method he considered was the simple mechanism envisaged by Frisch and Peierls in their memorandum, in which a small ‘bullet’ of the material is fired into a subcritical mass, thus making it supercritical. This had the advantage of being very straightforward, but the disadvantage of posing enormous ordnance problems, namely those of designing and manufacturing a ‘gun’ capable of firing the ‘bullet’ sufficiently quickly to prevent the bomb fizzling before it exploded. Another method discussed by Serber was the ‘implosion’ method, which was eventually used in the world’s first atomic-bomb explosion in July 1945. In this method pieces of the material are arranged in a circle and then brought together very quickly.

Though it has long been associated with Seth Neddermeyer, implosion was not invented by him, but rather by Richard Tolman, who suggested it at the Berkeley conference in 1942. Tolman and Serber collaborated on a memorandum on the subject at that time and, when urged by Conant and Bush to pursue the method in March 1943, Oppenheimer replied: ‘Serber is looking into it.’ In Oppenheimer’s original organisational chart of Los Alamos, the investigation of implosion was one of the things that was earmarked as Serber’s responsibility. Neddermeyer, however, became an enthusiastic advocate of the idea after hearing Serber’s lecture, and immediately dedicated himself to its development.

Neddermeyer’s development of the implosion concept was presented to the other scientists at Los Alamos at a major ten-day conference that began the day after Serber’s lectures finished. From 15 to 24 April, while the laboratories were still being built and the infrastructure of the growing town of Los Alamos was still being developed, an extraordinary collection of the best scientists in America – both native Americans and émigrés, those now working on the programme and those still working at their own universities – met to discuss the scientific questions that needed to be answered if an atomic bomb was ever going to be built.

On the first day of the conference, Oppenheimer, covering some of the same ground as Serber, summarised the present state of knowledge. With regard to the production of fissionable material by the enormous plants being constructed at Oak Ridge and Hanford, he told his audience that he estimated that from early 1944 100 grams of uranium-235 and, a year later, 300 grams of plutonium could be shipped every day. Oppenheimer also discussed the ‘Super’ that had so captured Teller’s imagination the previous summer, but insisted that it was at a much earlier stage of development than ‘the gadget’ and, as such, of decidedly secondary importance. On the two subsequent days Manley laid out the details of the forthcoming experimental programme, and Bethe discussed the physical constants that needed to be discovered, such as the critical mass, the number of neutrons emitted per fission, the various cross-sections and the efficiency of the explosion. On day four Serber led a discussion on the tamper. The issues covered in subsequent discussions included: experimental methods, the properties of natural uranium, detonation by gun method, the chain reaction produced by ‘the pile’ at Chicago, and, finally, the ways in which the critical mass, timescale and damage of the bomb might be discovered experimentally.

It was, of course, soon after this conference that Condon left the project, which made some reorganisation necessary. Back in November 1942, Conant had convened a committee to review progress in the various research projects then under way relating to the production of an atomic bomb. Chaired by Warren K. Lewis, a professor of chemical engineering at MIT, this review committee produced a report on 4 December, recommending the continuation of a concerted programme of plutonium production via the pile process then being pursued by Fermi at Chicago. In May 1943, a second Lewis committee was given the task of reviewing the Los Alamos programme. Up until then, the running of the laboratory had been the responsibility of a planning board, the membership of which had grown steadily. At its first meeting of 6 March 1943, the planning board had consisted of Oppenheimer, Condon, Wilson, McMillan, Manley and Serber. A few weeks later, this board had grown in two directions: Oppenheimer and Condon heading a subgroup concerned with the
administration of the laboratory, while Wilson, Serber and others took responsibility for planning the scientific programme. At two subsequent meetings in early April, several more scientists were added to the board, including Feynman, Teller, Bethe and Neddermeyer. Now, in addition to planning the first three months of the experimental programme, due to start in June, the board also discussed the problems that arose from the rapid expansion of the laboratory. Already it had 150 members of staff, and the available housing was almost filled. The board decided to delay any further hiring and recommended that the laboratory should ‘be more far-sighted about expansion’ in the future.

Members of the Lewis committee attended these planning board meetings, after which they produced a report that judged progress to be satisfactory, but recommended that the laboratory should be considerably expanded so as to include within its remit not only the design and manufacture of the bomb, but also, for example, the investigation of the metallurgy and purification of plutonium (previously chiefly the responsibility of the Met Lab in Chicago) and all issues relating to the ordnance of the bomb – that is, the design and manufacture of the specific mechanisms for firing and using the bomb. As the official history puts it, this report destroyed altogether ‘the original concept of Los Alamos as a small physical laboratory’.

Prior to the Lewis committee’s report, ordnance had been the responsibility of Richard Tolman and was treated as a scientific set of problems. The report, however, reflected Groves’s view that ordnance needed to be dealt with by someone with a practical rather than a purely scientific frame of mind, ‘so that,’ as Groves put it, ‘we will have service equipment instead of some dream child’. The kind of person Groves wanted ‘would have to set up ballistic tests of experimental bombs, plan for the combat use of the weapon and quite possibly be the one to use the bomb in actual battle’. In other words, it had to be a military man.

After trying and failing to find someone he thought could do the job, among the list of army ordnance officers, Groves turned to Bush in Washington, who recommended a naval officer: Commander William ‘Deak’ Parsons, a man with several years’ experience of ordnance and gunnery research. On 5 May 1943, Parsons was ordered to report without delay to Admiral Ernest King, and, he later recalled, ‘I was plunged into the Manhattan District with a set of verbal orders and a discussion with Admiral King lasting less than ten minutes.’ Groves, in his autobiography, says that, on meeting Parsons, he was immediately impressed with his ‘understanding of the interplay between military forces and advanced scientific theory’ and claims that ‘within a few minutes I was sure that he was the man for the job’.

The following day, Parsons was introduced to Oppenheimer and the
two of them took the train together to Los Alamos. During the journey, Parsons has recalled, they agreed that, while the scientists would ‘produce the nuclear guts of the gadget’, Parsons’s division would be responsible for engineering those guts into ‘a totally reliable service weapon’. Parsons had no background in nuclear physics, but what he, with his background in ordnance, could see that the scientists had not, even now, appreciated was the scale of the task facing them. When Parsons first arrived at Los Alamos in May 1943, Oppenheimer’s plan of the laboratory had swollen from his original conception of about a dozen scientists and staff to a workforce of about 300 people. A few days later, as a result of Parsons’s reappraisal of the situation, the anticipated workforce had more than doubled, most of the increase going into the ordnance-engineering division. After sizing up the situation at Los Alamos, Parsons returned to Washington for a few weeks. When he reported for work at Los Alamos in June, he had been promoted to captain, and made it clear to everyone that he regarded himself as firmly in charge of his part of the operation. Working under him, as group heads, were Ed McMillan, Charles Critchfield and Seth Neddermeyer, the last of whom had by this time become head of the Implosion Experimentation Group. Within two months, Parsons had added five more groups to his division and, in the words of his biographer, ‘pulled together a top-notch ordnance-development team, [begun] the design of the nuclear gun, brought new support to the implosion method of nuclear assembly, readied the test range at Anchor Ranch, [begun] the planning for the tactical delivery of the bomb, and started testing scale models’. Considering there was at this time almost no uranium, and absolutely no plutonium available for experiments, this was pretty remarkable progress.