The Making of the Atomic Bomb

In September 1942, Groves acquires nearly 60,000 acres of land just west of Knoxville, Tennessee. There, he builds a town, Oak Ridge, fills it with 20,000 workers, and erects a set of large factory buildings in which electromagnetic mass spectrometers pull U235 from uranium ore for use in an atomic bomb. The process is painstaking and slow, and problems with machinery set the project back by a month. Another method, gaseous diffusion, uses porous barriers to coax U235 from its cousin, U238. The difference between the isotopes is so small that the diffusion process must be repeated on the same gas over and over; production facilities involve “miles and miles of pipes and pumps and barriers” (494). Seals must be greaseless; a new plastic is invented for the purpose, later named Teflon. A huge factory, half a mile long and four stories tall, is built at Oak Ridge to do the work.

Plutonium is too dangerous to produce upwind of the city of Knoxville, so Groves’ team finds a remote site, Hanford, on a bend of the Columbia River in the desert of Washington state where they erect large buildings to house reactor piles cooled by river water. These piles are so much larger than Fermi’s original Chicago experiment that he calls them “different animals.”

Szilard wants firstly to beat the Germans, secondly to lift restrictions on freedom of discussion among the cloistered scientists, and lastly to ensure the public becomes deeply aware of the dangers of nuclear weapons. He also worries that immigrant scientists are being left out of the research, their contributions wasted. Groves believes Szilard is a security risk and has him followed. Many bureaucratic battles occur, with letters flying back and forth between Szilard, Groves, Compton, and Bush, especially over patent rights and compensatory salary raises. Szilard finally turns over his patents for the duration in exchange for cash and reemployment on the project.

Fermi wonders if Germany might already be breeding plutonium simply to spread onto American cities. Signs point to a German secret weapon—it will turn out to be V-1 and V-2 rockets, not an atomic bomb—and England, much closer to Germany than the US, has reason to fear. German heavy-water production at the sabotaged Norwegian plant starts up again in April 1943, much sooner than expected. American warplanes bomb the plant in November 1943, causing serious damage. The Nazis try to move what was left of the heavy water back to Germany by train, but Allied saboteurs sink the ferry carrying the train cars. The German dream of a nuclear weapon sinks with it. In the Pacific theatre, Marines quickly learn that Japanese soldiers almost always refuse to surrender but instead fight until they are killed. As Allied forces move closer to Japan, the military wonders whether Japanese civilians will be as hard to subdue when finally they are invaded. Americans begin to consider aerial bombardment against Japanese cities. 

The US agrees to share its knowledge of atom bombs with Britain; to that end, a delegation of English scientists, including newly sworn-in British citizen Otto Frisch, sail for America. Frisch is first to arrive at Los Alamos, in December 1943, followed by Bohr and Bohr’s son Aage, who bring a drawing by Heisenberg of a German nuclear reactor configured as a bomb. Either the Germans are way behind in nuclear technology or Heisenberg is trying to mislead Bohr.

To the young scientists troubled by the dark path physics has taken at Los Alamos, Bohr’s presence is reassuring. He reminds them of the evil represented by Hitler, and that work on the bomb is part of the great effort to put an end to the Nazi scourge. Bohr also meets with an old friend, Roosevelt confidante and Supreme Court associate justice Felix Frankfurter, to whom Bohr relays what he terms his “revelation” that the bomb can be used both for good and evil. Frankfurter talks about this with Roosevelt, who admits that the whole thing has “worried him to death” (526).

Bohr meets with Roosevelt; they discuss ways to prevent future nuclear proliferation. Bohr then flies to London in March 1944 with a message from Roosevelt to Churchill, asking him to consider early arms talks with Russia. Churchill meets with Bohr in May but angrily dismisses the message, saying that “this new bomb is just going to be bigger than our present bombs. It involves no difference in the principles of war” (530).

Just after the D-Day invasion begins, Bohr returns to Washington, his mission a failure, but Roosevelt is amused by Churchill’s pugnaciousness. Bohr writes a memorandum that warns that nuclear weapons promise, not security, but annihilation, and suggests that an international program of arms restrictions and inspections be undertaken. The consortium of nations that results might thereafter solve other international problems. Roosevelt reads the memorandum and meets with Bohr, telling him he concurs and expects Churchill to come around in good time. In September, however, when the president meets with Churchill, the prime minister nixes the disarmament idea, and Bohr's work is for naught.

At Los Alamos, personality conflicts erupt among a few of the major scientists; Oppenheimer works carefully to defuse these tiffs, moving men to different positions. One physicist, Teller, relocates from his work on high-explosive compression to theoretical fusion studies for a fusion bomb, the “Super.” Experiments suggest that plutonium fired into uranium will melt before it goes critical. Efforts shift toward a plutonium implosion bomb. Meanwhile, uranium enrichment efforts run slowly until the scientists realize they can combine enrichment processes in series, starting with thermal diffusion pipes that quickly provide small amounts of slightly enriched material for further purification in cyclotrons.

By the summer of 1944, US forces have advanced across the Pacific, conquering the Marianas, a group of islands 1,500 miles southeast of Japan, where on the island of Tinian they build airfields for bombing runs on the enemy homeland. In September 1944 at Hanford, a large reactor is ramped up to criticality. Cooled by water from the nearby Columbia River, the pile generates 100 megawatts of power and begins to produce plutonium as a decay product. Strangely, the reactor quickly declines in power, but several hours later it starts up again, then declines, as if breathing.

Fermi and Princeton’s John Wheeler figure out that a daughter product of the chain reaction, xenon, is absorbing neutrons and stopping the process, then decaying away and the pile goes critical again. Luckily, extra channels have been drilled into the pile for additional control rods; these help further to regulate the process. By December, plutonium production is in full swing, and enough material for 18 bombs will be ready by summer 1945.

In September 1944, Bush and Conant realize that Russia will, one way or another, soon develop their own atomic weapons. They send a memorandum to War secretary Stimson that suggests, much as Bohr proposed to Roosevelt and Churchill, that a treaty with the Soviets might forestall a future nuclear arms race.

At Los Alamos, as hard as they work during the week, the scientists play hard at Saturday night parties, and go hiking, riding, and fishing on Sundays. A house cat suffers radiation poisoning; they keep it alive as long as possible to learn about the symptoms. Oppenheimer comes into his own as Los Alamos director, his great mind able to keep track of everyone and everything important at the lab, the old brusqueness replaced by warm concern for his workers. The Army and FBI keep him under surveillance, however, due to his Communist sympathies.

The implosion group continues to study the compression of spheres of material by high explosives. X-rays record the detonations. In the bomb, the material will consist of an inner core of plutonium and polonium surrounded by natural uranium; a surrounding shell of explosives will compress the uranium onto the inner core, causing a near-instant and massive chain reaction. Shaping the explosion so it works precisely and efficiently—anything less will deliver a dud—is painstaking work.

By late 1944, lieutenant colonel Paul Tibbets, possibly the best bomber pilot in the American Air Force, has collected 1,767 enlisted men and officers and begun training crews in the Utah desert to deliver the atomic bomb from specially modified B-29 bombers. Early in 1945, B-29s commanded by General Curtis LeMay, flying from Tinian, begin attacking Japanese cities with incendiary bombs. The goal is to destroy heavy industry, but the March 10 night raid on Tokyo in six hours burns 15 square miles of the city, kills 100,000, wounds a million more, and destroys 1 million homes. Many more cities suffer the same fate in March until the US runs out of bombs.

At the Hanford facility, plutonium and its decay products, highly radioactive, must be separated chemically by remote control in stainless steel tanks inside huge buildings made of concrete walls several feet thick. As the Allies advance through Germany in 1945, a team of intelligence officers locates a huge cache of uranium ore, a water-cooled reactor that hadn’t yet achieved criticality, and a group of nuclear scientists, including Hahn and Heisenberg. The American team sends the uranium to Oak Ridge and sequesters the scientists before Soviet armies can get to them. On April 12, 1945, Roosevelt suffers a massive brain hemorrhage and dies. Much of the world mourns his passing as the leader of the fight against evil. The American vice president, Harry Truman, assumes the presidency. The work of the war continues.