In the months following the bombing of Pearl Harbor the Manhattan Project-the name given to The atomic bomb program because its original offices were in Manhattan – grew very quickly.
And although the Army had been involved since June of 1942, it was just beginning to realize that someone was going to have to be put in overall charge. The man chosen was Leslie Richard Groves, a 46-year-old colonel in the ArmyWhile he was a competent engineer, Groves was no scientist. He did not understand the science behind building the atomic bomb, nor did he pretend to. He needed someone who would be able to supervise the scientific side of the project. After dismissing a number of candidates, Groves decided on who seemed like the most improbable of candidates of all–38-year-old J. Robert Oppenheimer.
After he was officially given the job of laboratory director, Oppenheimer planned a campaign of absolutely unscrupulous recruiting of anyone we can lay our hands on. 1 He used his charismatic personality to recruit some of the greatest scientific talent in the world to join the project. He then helped Groves find a location for his bomb-making laboratory, tentatively called Site Y. A number of southwestern sites were explored.
On November 16, Oppenheimer,Groves, and representatives from the Army Corps of Engineers were looking at a site at Jemez Springs, New Mexico, a deep canyon about 40 mi. (64 km) northwest of Santa Fe. Oppenheimer did not care too much for the site, nor did Groves. His main objection was that there was no room for expansion. Oppenheimer then innocently remarked about going back to Albuquerque via the Los Alamos Ranch School.
Groves liked Los Alamos at once, and began moving quickly. He called Washington that very evening and began to buy the land. The Ranch School was having financial trouble as a result of the war, and so it was more than happy to sell out. Within a week, the land, the building, and other possessions of the school–including 1,600 books Los Alamos, or the Hill, as it was commonly referred to, officially opened for All bombs, and especially those being developed at Los Alamos, release energy in A certain amount of energy, called the binding energy, is required to hold the nucleus of an atom together. This energy is relatively small for light elements and steadily increases for heavier elements as far as cobalt, iron, and nickel.
After that, in still heavier elements, it begins to decrease to the point that the binding energy of an extremely heavy atom, such as uranium, is less than that of many, much lighter elements. A small portion of the mass of each particle is lost when it enters a nucleus so that a proton, for instance, actually weighs less inside the nucleus than outside. It must do this to fit in. To do this, it converts some of its mass into energy. The combined mass loss of all the particles of the nucleus equals the binding energy.
There are two processes by which particles can be made to lose weight. One, called fission (the type of bombs dropped on Japan), happens when a heavy nucleus splits apart into two lighter nuclei. These newly formed nuclei have a higher binding energy than their heavier parent nucleus; therefore, they demand a further weight loss on the part of their particles. The other process, called fusion, occurs when two light nuclei fuse together to form a single heavier nucleus with a higher binding energy. In both cases, the particles must lose mass and release energy. Certain types of atoms with many protons and neutrons in their nucleus are radioactive; they are unstable and may break apart spontaneously.
Other types, upon absorbing neutrons, break apart. In this process, the entire nucleus falls apart into two pieces, releasing energy in the process, but only after the nucleus temporarily increases its mass number by one. Two atoms, P-239 and U-235, undergo this type of division and release energy at the same time. U-235 emits two or three neutrons in the process, while P-239 emits many more. Either of these two atoms may be used in an atomic bomb. After absorbing a neutron, an atom of these elements emits several more neutrons, making a chain reaction possible.
If the surrounding structure is properly designed, the result is an explosion. The amount of fissionable material needed to make an explosion is called the critical mass, or the trigger quantity.