Shangri La (CV 38) - Naval Cruise Book

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l . ll v K Y l l V N l .L-- l.. Ski Party. made to occur on a large scale. The basic knowledge existed, but the know-how did not. Prior to the outbreak of war physicists exchanged papers on nuclear physics in a spirit of scientific collaboration. Germany's march into the Lowland countries served to put the lid of security on all American, French and United Kingdom nuclear advancements and the all-important race for the atomic bomb commenced. The Navy Department became interested in the project in the spring of 1940 after a conference with Einstein, Wigner, Pegram and several other nuclear sci- entists. The late President Roosevelt appointed a committee which resulted in the organization known as the Uranium Committee, under the National Defense Research Committee, and arranged for transfer of funds for experimentation. Experiments to date pointed to the probability of four Hssionable elements capable of the self-sustaining chain reaction necessary for an efficient bomb: Uranium QU-2359, obtained from the fission of 140 times more Uranium-238 in the natural state, protoactinium, discarded because of its rarity in nature: thorium, obtainable from monazite sands, was by-passed because of the require- ment of very high-energy neutrons for fission. The story of the creation of plutonium, an element which does not appear in nature but is a true trans- uranic element obtained from the Hssion of uranium, is one of the most romantic stories connected with the atomic bomb development. Plutonium was chosen

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as the practical source of iissionable material for the atomic bomb as it is formed from raw uranium and can be separated chemically. Early research by theoretical physicists established the necessity of obtaining uranium, or uranium oxide, refined to a state of over ninety-nine per cent purity. This heavy element had been used to some extent in the ceramics industry but impuritis in the normal commercial oxide were too great Qtwo- to- five per centj to produce U235 and Pu239. The problem of reiinement was solved by the use of an ether extraction, uranyl nitrate, providing better than ninety-nine per cent purity. By the summer of 1942 commercial chemists were producing usable uranium at the rate of a ton per day, solving the quantity production problem of this strategic and important metal. The immediate purpose of the pure uranium was the construction of piles, a lattice of uranium imbedded in graphite moderator blocks forming an oblate spheroid, like a tennis ball at the moment of impact. The use of the light element of carbon Cgraphitej was determined by its characteristic of retarding the speed of neutrons by elastic collision, allowing the operation of the pile at slow speed and temperature. Several other light elements operate even more efficiently, espe- cially deuterium oxide, or heavy water. However, a decision had to be made early for the material for this pile, so graphite was chosen as it was available whereas heavy water was not. Deuterium, which is an isotope of hydrogen, occurs in water, one part in 5,000. At the start of the war only a few litres were available, those being smug- gled out of Norway where the only commercial processing plants in existence were then in operation. The first chain-reacting pile was constructed on a squash court under the west stands of the University of Chicago stadium by Dr. E. Fermi and his col- laborators, under the overall direction of Dr. A. H. Compton. The pile consisted of 12,400 pounds of metal using graphite as a moderator, employing cadmium strips as control bars. Cadmium strips were placed at various intervals through the lattices, accelerating or decelerating by withdrawing or inserting these Sailors entertain orphans for Christmas.