|Fig. 1: Leo Szilard, around 1960. (Source: Wikimedia Commons)|
Leo Szilard (Fig. 1) was a physicist and inventor who is known as having played pivotal roles in the conception of the nuclear reactor as well as a key player in the creation of the the Manhattan Project that would later build the atomic bomb. He is credited with having discovered the nuclear chain reaction in 1933, as well as a fellow patent of the nuclear reactor with Enrico Fermi in 1939. Overall, Szilard was part of many milestones in nuclear technology.
Szilard spent his early years studying engineering, but transitioned into physics later. He studied engineering in Berlin at the Institute of Technology and then proceeded to gain his doctoral degree studying physics. His postdoctoral work brought him to the Kaiser Wilhelm Institute in Berlin, where he focused on studying the scattering and polarization of X-rays on crystals. In 1933, after Hitler rose to prominence in Germany, Szilard moved to England; there, he worked together with various firms to register patents through England, working as a research physicist at the Clarendon Laboratory in Oxford University. 
In October 1933, Szilard first conceived a nuclear chain reaction on the streetside corner of London. At Columbia University, Szilard worked together with Walter Zinn; in researching neutron emissions, they discovered that the element uranium might possibly be the key to sustaining a chain reaction, and that two neutrons are emitted in the fission process. Together with Enrico Fermi and Herbert Anderson, the team was able to construct a system of water and uranium oxide to be a model for a self-sustaining chain reaction.  Szilard was instrumental in building Chicago Pile-1, which was the first neutronic reactor that had self-sustaining nuclear chain reaction capabilities. In collaboration with Enrico Fermi, Szilard was able to deduct how uranium was able to sustain the chain reactions and be an effective tool for the creation of nuclear weapons.  Fermi and Szilard worked together and were granted the patent for a neutronic reactor in 1955. 
Although Szilard was among the first in discovering the possibility of creating a device that would utilize the nuclear chain reaction to fuel the bomb. But, as someone who lived through Hungary's political and economic turmoil, Szilard was very much against the use of the atomic bombs for its potential in negatively affecting innocent civilians. Szilard voiced his protests against the use of the atomic bombs in Nagasaki and Hiroshima in World War II. Unsuccessfully, he passed around petitions asking for greater scientific input on preventing the future use of atomic weapons. 
Szilard spent much of his career helping other scholars and refugees during the times of war and strife throughout World War II. At the risk of his own safety and career, Szilard was responsible for helping many scientific colleagues to obtain positions. He was monumental in organizing groups and initiating the Academic Assistance Council, which was a group spearheaded by scientist Ernst Rutherford to aid refugee scientists in finding new jobs. 
Szilard was a significant figure in his discoveries in nuclear physics, his role in initiating the Manhattan Project in World War II, and his opposition to the use of the atomic bomb during the era after World War II. Over the years, Szilard applied for a wide variety of patents and largely contributed to discovering scientific concepts that lie in the field of thermodynamics and nuclear chain reactions.
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 L. Szilard, "Memorandum," Leo Szilard Papers, University of California at San Diego Library, 13 Jun 56.
 J. Ottaviani et al., Fallout: J. Robert Oppenheimer, Leo Szilard, and the Political Science of the Atomic Bomb (G.T. Labs, 2001).
 W. Lanouette and B. Silard, Genius in the Shadows: A Biography of Leo Szilard, the Man Behind the Bomb (Skyhorse Publishing, 2013)