Leo Szilard

Leo Szilard (/ˈsɪlɑːrd/; Hungarian: Szilárd Leó, pronounced [ˈsilaːrd ˈlɛoː]; born Leó Spitz; February 11, 1898 – May 30, 1964) was a Hungarian-American physicist and inventor. He conceived the nuclear chain reaction in 1933, patented the idea of a nuclear fission reactor in 1934, and in late 1939 wrote the letter for Albert Einstein‘s signature that resulted in the Manhattan Project that built the atomic bomb. According to György Marx he was one of the Hungarian scientists known as The Martians.[1]

Hungarian-American physicist and inventor

The native form of this personal name is Szilárd Leó. This article uses Western name order when mentioning individuals.
Leo Szilard
Leó Szilárd

Szilard, c. 1960
Leó Spitz

(1898-02-11)February 11, 1898

Died May 30, 1964(1964-05-30) (aged 66)

  • Hungary
  • Germany
  • United States
Alma mater
Known for
Awards Atoms for Peace Award (1959)
Albert Einstein Award (1960)
Scientific career
Fields Physics, biology
Thesis Über die thermodynamischen Schwankungserscheinungen (1923)
Doctoral advisor Max von Laue
Other academic advisors Albert Einstein

Szilard initially attended Palatine Joseph Technical University in Budapest, but his engineering studies were interrupted by service in the Austro-Hungarian Army during World War I. He left Hungary for Germany in 1919, enrolling at Technische Hochschule (Institute of Technology) in Berlin-Charlottenburg, but became bored with engineering and transferred to Friedrich Wilhelm University, where he studied physics. He wrote his doctoral thesis on Maxwell’s demon, a long-standing puzzle in the philosophy of thermal and statistical physics. Szilard was the first to recognize the connection between thermodynamics and information theory.

In addition to the nuclear reactor, Szilard coined and submitted the earliest known patent applications and the first publications for the concepts of electron microscope (1928), the linear accelerator (1928), and the cyclotron (1929) in Germany, proving him as the originator of the idea of these devices. Between 1926 and 1930, he worked with Einstein on the development of the Einstein refrigerator. After Adolf Hitler became chancellor of Germany in 1933, Szilard urged his family and friends to flee Europe while they still could. He moved to England, where he helped found the Academic Assistance Council, an organization dedicated to helping refugee scholars find new jobs. While in England he discovered a means of isotope separation known as the Szilard–Chalmers effect.

Foreseeing another war in Europe, Szilard moved to the United States in 1938, where he worked with Enrico Fermi and Walter Zinn on means of creating a nuclear chain reaction. He was present when this was achieved within the Chicago Pile-1 on December 2, 1942. He worked for the Manhattan Project‘s Metallurgical Laboratory at the University of Chicago on aspects of nuclear reactor design. He drafted the Szilard petition advocating a demonstration of the atomic bomb, but the Interim Committee chose to use them against cities without warning.

After the war, Szilard switched to biology. He invented the chemostat, discovered feedback inhibition, and was involved in the first cloning of a human cell. He publicly sounded the alarm against the possible development of salted thermonuclear bombs, a new kind of nuclear weapon that might annihilate mankind. Diagnosed with bladder cancer in 1960, he underwent a cobalt-60 treatment that he had designed. He helped found the Salk Institute for Biological Studies, where he became a resident fellow. Szilard founded Council for a Livable World in 1962 to deliver “the sweet voice of reason” about nuclear weapons to Congress, the White House, and the American public. He died in his sleep of a heart attack in 1964.

. . . Leo Szilard . . .

He was born as Leó Spitz in Budapest, Kingdom of Hungary, on February 11, 1898. His middle-class Jewish parents, Lajos (Louis) Spitz, a civil engineer, and Tekla Vidor, raised Leó on the Városligeti Fasor in Pest.[2] He had two younger siblings, a brother, Béla, born in 1900, and a sister, Rózsi, born in 1901. On October 4, 1900, the family changed its surname from the German “Spitz” to the Hungarian “Szilárd”, a name that means “solid” in Hungarian.[3] Despite having a religious background, Szilard became an agnostic.[4][5] From 1908 to 1916 he attended Reáliskola high school in his home town. Showing an early interest in physics and a proficiency in mathematics, in 1916 he won the Eötvös Prize, a national prize for mathematics.[6][7]

Leo Szilard aged 18

With World War I raging in Europe, Szilard received notice on January 22, 1916, that he had been drafted into the 5th Fortress Regiment, but he was able to continue his studies. He enrolled as an engineering student at the Palatine Joseph Technical University, which he entered in September 1916. The following year he joined the Austro-Hungarian Army‘s 4th Mountain Artillery Regiment, but immediately was sent to Budapest as an officer candidate. He rejoined his regiment in May 1918 but in September, before being sent to the front, he fell ill with Spanish Influenza and was returned home for hospitalization.[8] Later he was informed that his regiment had been nearly annihilated in battle, so the illness probably saved his life.[9] He was discharged honorably in November 1918, after the Armistice.[10]

In January 1919, Szilard resumed his engineering studies, but Hungary was in a chaotic political situation with the rise of the Hungarian Soviet Republic under Béla Kun. Szilard and his brother Béla founded their own political group, the Hungarian Association of Socialist Students, with a platform based on a scheme of Szilard’s for taxation reform. He was convinced that socialism was the answer to Hungary’s post-war problems, but not that of Kun’s Hungarian Socialist Party, which had close ties to the Soviet Union.[11] When Kun’s government tottered, the brothers officially changed their religion from “Israelite” to “Calvinist“, but when they attempted to re-enroll in what was now the Budapest University of Technology, they were prevented from doing so by nationalist students because they were Jews.[12]

Convinced that there was no future for him in Hungary, Szilard left for Berlin via Austria on December 25, 1919, and enrolled at the Technische Hochschule (Institute of Technology) in Berlin-Charlottenburg. He was soon joined by his brother Béla.[13] Szilard became bored with engineering, and his attention turned to physics. This was not taught at the Technische Hochschule, so he transferred to Friedrich Wilhelm University, where he attended lectures given by Albert Einstein, Max Planck, Walter Nernst, James Franck and Max von Laue.[14] He also met fellow Hungarian students Eugene Wigner, John von Neumann and Dennis Gabor.[15]

Szilard’s doctoral dissertation on thermodynamicsÜber die thermodynamischen Schwankungserscheinungen (On The Manifestation of Thermodynamic Fluctuations), praised by Einstein, won top honors in 1922. It involved a long-standing puzzle in the philosophy of thermal and statistical physics known as Maxwell’s demon, a thought experiment originated by the physicistJames Clerk Maxwell. The problem was thought to be insoluble, but in tackling it Szilard recognized the connection between thermodynamics and information theory.[16][17] Szilard was appointed as assistant to von Laue at the Institute for Theoretical Physics in 1924. In 1927 he finished his habilitation and became a Privatdozent (private lecturer) in physics. For his habilitation lecture, he produced a second paper on Maxwell’s Demon, Über die Entropieverminderung in einem thermodynamischen System bei Eingriffen intelligenter Wesen (On the reduction of entropy in a thermodynamic system by the intervention of intelligent beings), that had actually been written soon after the first. This introduced the thought experiment now called the Szilard engine and became important in the history of attempts to understand Maxwell’s demon. The paper is also the first equation of negative entropy and information. As such, it established Szilard as one of the founders of information theory, but he did not publish it until 1929, and did not pursue it further. Claude E. Shannon, who took it up in the 1950s, acknowledged Szilard’s paper as his starting point.[18][19]

Throughout his time in Berlin, Szilard worked on numerous technical inventions. In 1928 he submitted a patent application for the linear accelerator, not knowing of Gustav Ising‘s prior 1924 journal article and Rolf Widerøe‘s operational device,[20][21] and in 1929 applied for one for the cyclotron.[22]He was also the first person to conceive the idea of the electron microscope,[23] and submitted the earliest patent for one in 1928.[24] Between 1926 and 1930, he worked with Einstein to develop the Einstein refrigerator, notable because it had no moving parts.[25] He did not build all of these devices, or publish these ideas in scientific journals, and so credit for them often went to others. As a result, Szilard never received the Nobel Prize, but Ernest Lawrence was awarded it for the cyclotron in 1939, and Ernst Ruska for the electron microscope in 1986.[24]

An image from the Fermi–Szilard “neutronic reactor” patent

Szilard received German citizenship in 1930, but was already uneasy about the political situation in Europe.[26] When Adolf Hitler became chancellor of Germanyon January 30, 1933, Szilard urged his family and friends to flee Europe while they still could.[19] He moved to England, and transferred his savings of £1,595 (£115,800 today) from his bank in Zurich to one in London. He lived in hotels where lodging and meals cost about £5.5 a week.[27] For those less fortunate, he helped found the Academic Assistance Council, an organization dedicated to helping refugee scholars find new jobs, and persuaded the Royal Society to provide accommodation for it at Burlington House. He enlisted the help of academics such as Harald Bohr, G. H. Hardy, Archibald Hill and Frederick G. Donnan. By the outbreak of World War II in 1939, it had helped to find places for over 2,500 refugee scholars.[28]

On the morning of September 12, 1933, Szilard read an article in The Times summarizing a speech given by Lord Rutherford in which Rutherford rejected the feasibility of using atomic energy for practical purposes. The speech remarked specifically on the recent 1932 work of his students, John Cockcroft and Ernest Walton, in “splitting” lithium into alpha particles, by bombardment with protons from a particle accelerator they had constructed.[29] Rutherford went on to say:

We might in these processes obtain very much more energy than the proton supplied, but on the average we could not expect to obtain energy in this way. It was a very poor and inefficient way of producing energy, and anyone who looked for a source of power in the transformation of the atoms was talking moonshine. But the subject was scientifically interesting because it gave insight into the atoms.[30]

Szilard was so annoyed at Rutherford’s dismissal that, on the same day, he conceived of the idea of nuclear chain reaction (analogous to a chemical chain reaction), using recently discovered neutrons. The idea did not use the mechanism of nuclear fission, which was not yet discovered, but Szilard realized that if neutrons could initiate any sort of energy-producing nuclear reaction, such as the one that had occurred in lithium, and could be produced themselves by the same reaction, energy might be obtained with little input, since the reaction would be self-sustaining.[31] Szilard filed for a patent on the concept of the neutron-induced nuclear chain reaction in 1933, which was granted in 1936.[32] Under section 30 of the Patents and Designs Act (1907, UK),[33] Szilard was able to assign the patent to the British Admiralty to ensure its secrecy, which he did.[34] Consequently, his patent was not published until 1949[32] when the relevant parts of the Patents and Designs Act (1907, UK) were repealed by the Patents Act (1949, UK).[35]Richard Rhodes described Szilard’s moment of inspiration:

In London, where Southampton Row passes Russell Square, across from the British Museum in Bloomsbury, Leo Szilard waited irritably one gray Depression morning for the stoplight to change. A trace of rain had fallen during the night; Tuesday, September 12, 1933, dawned cool, humid and dull. Drizzling rain would begin again in early afternoon. When Szilard told the story later he never mentioned his destination that morning. He may have had none; he often walked to think. In any case another destination intervened. The stoplight changed to green. Szilard stepped off the curb. As he crossed the street time cracked open before him and he saw a way to the future, death into the world and all our woe, the shape of things to come.[36]

In early 1934, Szilard began working at St Bartholomew’s Hospital in London. Working with a young physicist on the hospital staff, Thomas A. Chalmers, he began studying radioactive isotopes for medical purposes. It was known that bombarding elements with neutrons could produce either heavier isotopes of an element, or a heavier element, a phenomenon known as the Fermi Effect after its discoverer, the Italian physicist Enrico Fermi. When they bombarded ethyl iodide with neutrons produced by a radonberyllium source, they found that the heavier radioactive isotopes of iodine separated from the compound. Thus, they had discovered a means of isotope separation. This method became known as the Szilard–Chalmers effect, and was widely used in the preparation of medical isotopes.[37][38][39] He also attempted unsuccessfully to create a nuclear chain reaction using beryllium by bombarding it with X-rays.[40][41]

. . . Leo Szilard . . .

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. . . Leo Szilard . . .

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