The Manhattan Project: Making the Atomic Bomb

Part IV: The Manhattan Engineer District in Operation

Xenon Poisoning

Hanford scientists were at a loss to explain the pile's failure to maintain a chain reaction. Only the foresight of DuPont's engineers made it possible to resolve the crisis. The cause of the strange phenomenon proved to be xenon poisoning. Xenon, a fission product isotope with a mass of 135, was produced as the pile operated. It captured neutrons faster than the pile could produce them, causing a gradual shutdown. With shutdown, the xenon decayed, neutron flow began, and the pile started up again. Fortuitously, despite the objections of some scientists who complained of DuPont's excessive caution, the company had installed a large number of extra tubes. This design feature meant that pile 100-B could be expanded to reach a power level sufficient to overwhelm the xenon poisoning. Success was achieved when the first irradiated slugs were discharged from pile 100-B on Christmas Day, 1944. The irradiated slugs, after several weeks of storage, went to the chemical separation and concentration facilities. By the end of January 1945, the highly purified plutonium underwent further concentration in the completed chemical isolation building, where remaining impurities were removed successfully. Los Alamos received its first plutonium on February 2. 44

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