The Manhattan Project, Part Two: Building the Bomb
—Chrissie

Read Part One here: Splitting the Atom

Listen here: www.spreaker.com/user/bqn1/hwts192

            The work of designing and building the atomic bomb was not all done in one place. Los Alamos, New Mexico was where Oppenheimer set up shop and where the bomb itself was built, and it was tested at nearby White Sands, but components for it were produced all around the US and Canada. Some of these, like Los Alamos, were set up as entire communities. There was no telling how long the project would take, and it would be much easier to convince those working on it to be involved if they could bring their families. The Army Corps of Engineers procured most of this land via seizure through eminent domain. Los Alamos was built around what had been the Los Alamos Ranch School, a boarding school for wealthy teenage boys. There were also members of local tribes who were removed from the land that would become the project center. Construction began in November 1942 and people began moving in by February 1943

Setting up Los Alamos was not as disruptive to the local community as other sites would be. Oak Ridge, Tennessee, for example, was more complex. The area was appropriately far from large population centers, but the land wanted by the army was inhabited, in some cases by people whose families had been there for generations. Approximately three thousand people were forced out of their homes with a few weeks’ warning at best and almost no compensation. The area was made a complete exclusion zone by the Army, meaning no one could enter without permission of the military. Where these people had lived, a community for the expected 13,000 residents was built; by the end of the war, more than 75,000 lived and worked in Oak Ridge. Here, enriched uranium was produced with three different methods. The first, electromagnetic isotope separation, involved separating the uranium atoms with a calutron, a type of cyclotron developed by Earnest Lawrence at University of California at Berkeley (hence the name, Cal-U-tron). The Oak Ridge calutrons were first run by physicists, but they had a tendency to make adjustments to the equipment and try to repair it when it malfunctioned. These were replaced by young women who came to be called the Calutron Girls. Because most of them were right out of high school and so did not have a background in the sciences, they didn’t try to make changes or fix anything, making their work more efficient than their predecessors. The second method, gaseous diffusion, put uranium atoms into a gaseous state, allowing the isotopes to separate by their atomic weight. The third method, liquid thermal diffusion, was not terribly effective on its own, but made the gaseous diffusion more effective by starting the enrichment process.

Another of the production sites, Hanford, Washington, also saw population removal. Approximately 1500 people, most of them farmers who had already planted that year’s crops, were given short notice to leave. Some were able to return to tend and harvest their crops, but not all, and none were fully compensated for the loss. Additionally, the area was completely cut off from local tribes who had longstanding treaty rights to use it for hunting, fishing, and ceremonial purposes. Hanford produced plutonium for the project in three reactors set up along the Columbia River, a location chosen because of the availability of water to cool the nuclear reactors.

In the end, everything was directed to Los Alamos, where the bomb itself, called the “Gadget,” would be constructed. Oppenheimer initially estimated only 100 people would be needed for the work; by the time all was finished, the population of Los Alamos was about ten thousand, including the families of those employed in production of the Gadget. The initial setup for the Hill, as the inhabitants came to call it, was to be a military laboratory, requiring that the researchers become commissioned officers and submit themselves to the military hierarchy and chain of command. This did not sit well with many of the scientists, and so a compromise was made to organize it as a university lab funded by the Army. Security clearance for some of the scientists was difficult, even Oppenheimer himself had to wait, but General Groves opened the classified areas right away, with the understanding that clearance would come.

Oppenheimer’s core team consisted primarily of people already working on the project: his group from CalTech and Berkeley, researchers from University of Minnesota and University of Wisconsin (the latter team was led by Joseph M. McKibben, who would be the one to flip the switch to activate the Trinity test bomb), the group from Stanford under Felix Block, the metallurgical group that had already been working on the Project prior to setting up Los Alamos which included Edward Teller. From Princeton came Richard Feynman and the cyclotron they’d been using at Harvard. The wives of many of these men also found employment on the Hill, doing clerical work with the Project or doing the things needed in the community that were not directly Project-related, like teaching school. There were some women who worked on the Project itself, Lilli Horning, who had accompanied her husband to Los Alamos, held degrees in chemistry. When she asked to be included in the project work, she was initially assigned to the typing pool until she and her credentials were vouched for by the plutonium team.

The researchers were organized into groups for different elements of the research: Administration (A), Theoretical (T), Experimental Physics (P), Chemistry and Metallurgy (CM), and Engineering (E). there was also a British contingent who began as a separate group but were later integrated into the other groups according to their expertise, though their access to classified materials was limited. There was also research conducted on a hydrogen-based fusion method for a bomb, advocated for by Edward Teller, who was also one of the few people working on it. Oppenheimer didn’t think the hydrogen model was as viable as the fission method on which they were already working. This was a point of contention between the two men and would remain so long after the Manhattan Project was concluded.

I am not going to get into the particulars of the physics of the bombs, because I am not at all qualified to do so. I recommend Richard Rhodes’ Making of the Atomic Bomb for the non-physicists in our audience.

There were two potential designs for the bomb: the gun method, in which a sub-critical mass of the material (in this case, enriched uranium) is propelled into another causing a critical mass and fission. The second was implosion, in which explosives are used to push the material together, causing it to reach critical mass and beginning the nuclear chain reaction. The gun method was first built in a test device called Thin Man, and was used for Little Boy, the bomb that would be dropped over Hiroshima. This design worked as expected when using enriched uranium, but when they tried it with plutonium, they found it to be too reactive. Plutonium could only be used with an implosion device, and considerably less plutonium was needed to produce the same level of explosion as the gun method did with a great deal more enriched uranium. Work on an implosion bomb began in mid-1944, this is the type that would be tested at Trinity and dropped over Nagasaki. The gun-type, with its straightforward design, did not need a live test.

            On 7 May 1945, the war in Europe ended with the surrender of Germany. The atomic program had been conceived to make sure the Allies had the bomb before Germany did, but by this point, there was no reason to stop the work. Even though the war continued with Japan, the upper echelons of the US Military had begun to shift away from how to conduct this war toward how a future war with the USSR would be conducted.  The test was scheduled to occur before the Potsdam Conference, to allow President Truman to communicate that the Americans could produce the devastating weapon and thereby influence negotiations. The conference was set to begin on 16 July 1945, so the test was set for the day before.

            A location south of Los Alamos was chosen, the Alamogordo Bombing and Gunnery Range, now renamed White Sands Proving Grounds. The area had been   purchased by the US government in 1942 and had been used for testing other equipment. A thirty meter tall tower was built to simulate the bomb detonating above ground. Observation posts were laid out at 9100 meters due north, south and west of the tower. Another observation posts for VIPs, including Groves, Vannevar Bush, Isidor Rabi, and James Conant, was set up twenty miles northwest. All of the observers were issued welding goggles and placed with their backs turned to the explosion; they were not to look at the initial moment of it, but only after they could see light on the hills in front of them. Edward Teller kitted himself out with not only the welder’s goggles, but an additional pair of sunglasses beneath them, a pair of gloves, and sunscreen. He chose to watch the explosion itself, rather than have his back turned as was ordered by others at the observation post. Richard Feynman observed from a truck and declined the welder’s goggles, arguing that the windshield would protect him from any damaging UV waves; because of this, he was one of the few (possibly the only) who saw the explosion unfiltered. Two B-52 bombers circled the area of the test to collect data to determine the best location for targeting. Fifty cameras were set up at various locations to take not only photographs but measure various wavelengths across the spectrum.

            The Gadget was set off at 5:29 am Mountain time on 16 July. It produced a 24.8 kiloton explosion, a crater nearly eighty meters across with a depth of almost a meter and a half, and a mushroom cloud that reached seven and a half miles into the air. The ground for 3000 meters around the tower was turned to greenish glass which was slightly radioactive. The tower was vaporized. It took forty seconds for the shockwave to reach the observers and the blast was felt as much as 100 miles away. At the time, it was thought the fallout radiation would not go too far, and no real effort was made to measure it beyond the immediate area. Recent research has shown that the fallout reached across North America over the next week. The explosion was seen as far as fifty miles away, requiring a cover story about an accident at a munitions warehouse to be sent out. After the Hiroshima bombing, limited information about the Trinity test was made public, including a retraction of the cover story. 

            There was no question about the success of the test, and thus the success of the nuclear program. The Manhattan Project had done what it set out to do: build the bomb before the Germans. Now, the question was how, or whether at all, it should be used.