In our post two weeks ago, we mentioned implosion as an assembly method for a critical mass. The critical mass is the amount of fissile material—in the form of uranium or plutonium—necessary to set-up the uncontrolled fission chain reaction that’s at the heart of a nuclear weapon. Implosion was one of three original assembly methods evaluated during the Manhattan Project: autocatalysis, the gun method, and implosion. The scientists at Los Alamos, however, had no experience using explosives to systematically create the symmetric, spherical blast wave necessary to compress solid materials for implosion. Indeed, in one of the official histories of the Manhattan Project, David Hawkins says the following:
[T]he behavior of solid matter under the thermodynamical conditions created by an implosion went far beyond current laboratory experience. As even its name implies, the implosion seemed “against nature.”
Physicist Seth Neddermeyer was an early advocate of the implosion method, and he began a serious investigation of the process in 1943. By mid-1944, because of plutonium’s propensity for spontaneous fission, it became clearer that, if there was to be an atomic bomb that used plutonium, then implosion was the only viable assembly method. The progress that Neddermeyer’s team had made on the implosion problem was deemed to be inadequate, though, and Neddermeyer was replaced. The realization that implosion was an extremely complicated problem set off a reorganization of Los Alamos that saw the creation of entirely new research groups, promotion or hiring of scientists to lead those groups, and realignment within existing research groups.
What’s remarkable about the Los Alamos reorganization is the breadth of the changes and the speed with which they were executed in the fall of 1944. A letter in mid-June, a series of meetings in July, and final approval on July 20th, 1944—1, 2, 3, go. The changes required by the reorganization were considered to be in effect on August 14th, 1944. The gun design was considered to be making acceptable progress under the leadership of Navy Captain William “Deak” Parsons. Parsons had been in charge of the Ordnance Division, and perhaps the biggest change that underwent was becoming the O Division. The two most important of the newly created divisions were X Division and G Division. X Division—X for Explosives—was headed by Harvard physical chemist George Kistiakowsky. Kisti’s group was responsible for every engineering and development aspect of creating the explosive system used to render the implosion. G Division—G for Gadget—was led by Robert Bacher and became responsible for all of the aspects of the bomb that had to do with its nuclear core, the so-called plutonium pit. In addition, because of G Division’s responsibility for the pit, they were also charged with developing various experimental methodologies for evaluating the effectiveness of the implosion—in particular, measure for validating the compression of solid materials. Importantly, the series of organizational changes that enhanced the overall understanding of the implosion-based atomic bomb. So, existing divisions such as R Division (Research, the Experimental Physics Division prior to the reorganization) and T Division (Theory) adjusted as the focus on implosion took hold across the laboratory at Los Alamos.
The Manhattan Project’s leadership, spurred on by J. Robert Oppenheimer, saw a problem and worked effectively to address that problem. This speedy, drastic effort that reorganized the Manhattan Project reminds us of an engineering analogy that used to come up in computer systems development: replacing a car’s engine as you’re going down the highway at 70 mile per hour. Just over two months time elapsed from the proposed changes to their implementation, with research continuing all the while. The development of the implosion device, the Gadget, was the primary focus of the laboratory from this reorganization in August 1944 until the Trinity test of the first atomic weapon on July 16, 1945. The Countdown to the Cold War was well underway 70 years ago today.