The Hanford scientists were
at a loss to explain the pile's mysterious 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 again, and the pile started
up. 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 the
pile 100-B could easily 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
Los Alamos received its
first plutonium on February 2, 1945.