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River coursed through the tubes and around the cans, cooling the uranium as it reacted. Cooked in the reactor for at least 100 days, the canned slugs were pushed out of the back of the pile into pools to contain their radioactivity, and months later—two months were the minimum necessary for safety, with four more desirable—they were taken off to the separation plants to have their bits of plutonium teased out. From the start there was a serious glitch. The Hanford B reactor, run at full power as no test reactor had been previously, produced quantities of the element xenon, which absorbed neutrons and ‘poisoned’ the chain reaction. The engineers and scientists determined to overmatch the poisoning by stuffing more uranium slugs into extra tubes Du Pont had drilled into the graphite. The B reactor was restarted.41

In the summer of 1944 Oppenheimer recommended to Groves the preenrichment, by thermal (hot to cold plate) diffusion, of feed uranium for the Oak Ridge Calutrons. That made production of U-235 creep toward the level needed for a bomb—64 kilograms in the event. At Hanford, progress was steady once the xenon poisoning problem was solved, but still too slow for Groves’s taste. He ordered Du Pont officials to move things along: he needed roughly 6 kilograms for a test shot and another 6 for the first plutonium bomb. Du Pont obliged, with Groves’s permission, by taking shortcuts, among them reducing the amount of time workers left the radioactive slugs in their post-reactor baths. That greatly increased the danger to those who then transported the slugs to the separation plants, and especially to those who then removed the slugs from the aluminum cans, which meant dissolving the aluminum in acid. Groves decided he could live with the risk, and that his workers could too, especially if they were not informed of its possible magnitude. Los Alamos got its first delivery of Hanford plutonium in February 1945. Taken by convoy, escorted by men wielding shotguns and submachine guns, the stuff came in stainless steel flasks, each holding, writes Robert Norris, ‘eighty grams of the bluish green slurry’.42

9. Life and work on ‘The Hill’

The uranium and plutonium came into the eager hands of the men who were to build the bombs on the New Mexico mesa. ‘Oppenheimer’s Army’, they were called. Oppenheimer recruited his people in late 1942 and early 1943, and by spring they had started to turn up in Santa Fe. Lansing Lamont describes the arrival:

They filtered in by twos and threes: bewildered, sleepless, irritated men who had sold their homes, deceived their friends and families, and deserted laboratories and students to sally forth to an unmentionable spot that might as well have been in the land of the yeti. They arrived in the old Spanish capital after hours and days of fighting crowded trains, missed planes and flat tires.

They were instructed to go to 109 East Palace, an old Spanish house fronted by a courtyard. In a small room at the back of the yard they would be greeted by Dorothy McKibben, who would try to calm the physicists and answer their questions and place them at a local home until the next bus could take them to ‘Site Y’ or ‘The Hill’ as it came to be known, 35 miles to the northwest. Their address was now simply PO Box 1663, and they were never to address each other in town as ‘Doctor’ or ‘Professor’; the most famous of them were given pseudonyms. The bus ride up to the mesa, at 7,200 feet, was a sobering exercise in withdrawal from anything familiar, anything seemingly civilized. They entered the site through a security checkpoint at the eastern gate, which pierced the barbed-wire fence enclosing the newly sprung town.

Oppenheimer proved an effective recruiter. He signed up Hans Bethe and Edward Teller. Fermi promised to come when he could get away from his work at the Met Lab, and soon he and his wife, Laura, had moved to Los Alamos for the duration, taking over nondescript Apartment D in building T-186, rather than accepting a fancier cottage offered them: the Fermis wanted to avoid distancing themselves