Hanford, Washington State. The site’s first reactor (designated “B”) reaches criticality. Fermi is present. But the next morning it begins to lose power until it shuts down. Panic. $7 million ($95 million today) has been spent, and the government was spending another $350 million on other reactors of that type. It doesn’t work. Wheeler, fortunately, had been working on the reactor poisoning: fission byproducts steal neutrons, but the culprit for absorbing neutrons so voraciously must be found. The reactor itself provides an important clue: after several hours, it spontaneously ignites again, thus indicating the lifetime of the culprit. It is xenon-135, with a half-life of 9 hours. It is present in very small quantities and therefore had not been tested, but, it turns out, it has a neutron absorption power one hundred thousand times greater than cadmium! Reactor B, after appropriate modifications, reached criticality only in February 1945, by which time reactors D and F were also almost finished. And the Oak Ridge reactor had already been operating for months.
