PART I: Starting Point

Military & Scientific Realities of 1943

Military considerations had government the decision, by 1943, that an atomic bomb was desirable, as a means for bringing World War II to an end. Scientific considerations had governed the decision that an atomic bomb was probably feasible. Technological considerations (already being worried about, though they were almost entirely in the realm of the unknown) had made it obvious that the atomic bomb would not be built in a day or a month or a year.

The military picture was grim. The USA was at war with Japan, Germany, and Italy. American naval power had not yet recovered from the disaster at Pearl Harbor. The Japanese had conquered the Philippines, and Japanese naval power was at its height. American soldiers were heavily engaged in North Africa and elsewhere. The Germans had barely begun to suffer the reverses that would turn the tide of war against them. (They surrendered El Alamein late in 1942 and Stalingrad in 1943.) German scientists were working-no American knew how ineffectively-toward an atomic bomb.

The scientific picture was exciting. The phenomenon of uranium fission had been observed several years earlier and had been correctly interpreted before 1940. It was known that at least one kind of uranium nucleus would divide (roughly in half) upon absorption of a neutron, and that this reaction liberated energy plus more neutrons. In December, 1942, a Chicago group under Enrico Fermi had succeeded in bringing about the world’s first man-made nuclear chain reaction-a reaction in which the neutrons from fission caused further fission at a sustained level.

The technological picture was wry nearly a blank, so far as atomic bombs were concerned. This was true not only because no one had ever tried to build an atomic bomb, but because so much fundamental scientific research remained to be done before anyone ever could.

Enough was known already, to suggest the magnitude of the task, both scientifically and technologically. It was known, for instance, that the essential fissionable material-the heart of the bomb-would be hard to prepare.

Fermi’s historic “pile” consisted of graphite blocks and lumps of natural uranium. Natural uranium is more than 99% U-238, a heavy isotope unfit for use in a bomb because of its tendency to capture neutrons without fissioning. Uranium-235, the lighter isotope needed for a weapon, makes up about seven-tenths of one per cent of naturally-occurring uranium, Separating U-235 from the more abundant isotopes is extremely difficult, since the chemical behavior of the two isotopes offers no differences great enough to form the basis of an efficient chemical separation process.

Slight differences in physical behavior include the fact that atoms of U-235 diffuse through porous material at a somewhat faster rate than atoms of U-238, and also the fact that the trajectory of a fast-moving U-235 ion (an atom lacking one or more of its natural electrons) will bend slightly more, in a given transverse magnetic field, than the trajectory of any accompanying ions of U-238. Both of these slight behavioral differences (as well as others, even less promising) were under intensive study by 1941.

In 1943 a separation plant based on the different diffusion rates was built at Oak Ridge, Tennessee, to produce enriched uranium (uranium containing more than the natural proportion of U-235) for possible use in a weapon. At the time of the founding of the Los A1amos Laboratory, construction of the Tennessee plant had not yet begun. There was not enough enriched uranium in the world for a single bomb, or even for satisfactory laboratory investigations of U-235 behavior. Material for the first uranium bomb would not be ready for more than a year.

Minute quantities of a second fissionable element, plutonium, had been created at Berkeley in the winter of 1940-41. Plutonium does not occur in nature, but can be formed from uranium-238 through a complicated series of events beginning with the capture of neutrons by the uranium. The construction of nuclear reactors to furnish neutrons for this process began in 1943 at Oak Ridge, Tennessee (on a small scale) and Hanford, Washington (on a large scale). At the time of the founding of Los Alamos Laboratory, all the world’s plutonium could still have been piled on a pinhead, with room to spare.

Thus in January, 1943, not only was there no fissionable material for bomb-making; construction of the Tennessee and Washington plants from which the material would come had not even begun.

Methods of devising a bomb deriving its explosive energy from the fission of U-235 or Pu-239 were purely speculative. The engineering effort was entirely in the future, and it would depend heavily on the results of physical, chemical, and metallurgical studies of the two possible core materials. These studies would have to be made on extremely small quantities of uranium and plutonium, so that the necessary knowledge would be gained by the time larger quantities should become available.

Thus it was that the Los Alamos Laboratory, or Project Y as it was called, became the crucial part of a super-secret nationwide research and development program known as the Manhattan Engineer District of the War Department. While other groups worked toward development and production of materials, the mission of the Laboratory, under the direction of J. Robert Oppenheimer, was to pet-form the necessary research, develop the technology and then to produce the actual bombs in time to affect the outcome of the war. The story of how this was done, in the face of the problems just suggested and other problems soon to be encountered, has already become a classic of science and engineering. It begins with the choice of a site for the laboratory that was to become, in the words of Dr. I I. Rabi, “the first line of defense of the United States.”

As the following chapter will show, geology and geography played a remote but finite part in the selection of the location on the Pajarito Plateau in New Mexico’s Jemez Mountains-an isolated school for boys with “adequate quarters for the 30 scientists” who were all the project would need, or so the founding fathers thought.

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