Leó Szilárd

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Leó Szilárd


February 11 1898(1898-02-11)
Budapest, Austria-Hungary

Died May 30 1964 (aged 66)

La Jolla, California, U.S.

Residence Flag of the United States.svg U.S.
Nationality Flag of Hungary.svg Hungarian-Flag of the United States.svg American
Field Physicist, Biologist
Institutions Technical University of Berlin
Humboldt University of Berlin
Columbia University
University of Chicago
Brandeis University
Alma mater Technische Universität Berlin
Humboldt University of Berlin
Academic advisor  Max Von Laue Nobel Prize.png
Known for Thermodynamics, nuclear chain reaction
Religious stance Jewish

Leó Szilárd (Hungarian: Szilárd Leó) (February 11, 1898 – May 30, 1964) was a Hungarian-American physicist who conceived of the nuclear chain reaction and worked on the Manhattan Project. After World War II, he was struck by the horror of nuclear weapons. He switched his field from physics to molecular biology and became an advocate of rational arms control and nuclear disarmament.


Early life

Szilárd was born in Budapest at the time of the Austro-Hungarian monarchy, before World War I, as the son of a Jewish civil engineer. From 1908-1916, he attended Reáliskola in his home town. He was enrolled as an engineering student at Budapest Technical University in 1916, but had to join the Austro-Hungarian Army in 1917, as an officer-candidate, where he was honorably discharged at the end of the war. In 1919, he resumed engineering studies at Budapest Technical University but soon decided to leave Hungary because of the rising antisemitism under the Horthy regime which led to the introduction of a numerous clausus for Jewish students at Hungary's universities.

He continued engineering studies at Technische Hochschule (Institute of Technology) in Berlin-Charlottenburg. He soon changed to physics there and took classes from Einstein, Planck, and Max von Laue. His dissertation on thermodynamics, Über die thermodynamischen Schwankungserscheinungen (On The Manifestation of Thermodynamic Fluctuations) in 1922, was praised by Einstein and awarded the highest honor. In 1923, he received a doctorate in physics from the Humboldt University of Berlin. He was appointed as assistant to von Laue at the University of Berlin's Institute for Theoretical Physics in 1924. In 1927, he finished his habilitation and became a Privatdozent (instructor) in Physics at University of Berlin. During his time in Berlin, he was working on numerous technical inventions (1928 German patent application on the linear accelerator, 1929 German patent application on the cyclotron, since 1926, work with Einstein on the construction of a refrigerator without moving parts (US patent number 1,781,541 on November 11, 1930).

Developing the idea of the nuclear chain reaction

Nuclear reactor team at the University of Chicago. Back row, from left: Norman Hilberry, Samuel Allison, Thomas Brill, Robert Nobles, Warren Nyer, and Marvin Wilkening. Middle row: Harold Agnew, William Sturm, Harold Lichtenberger, Leona Woods and Leo Szilard. Front row: Enrico Fermi, Walter Zinn, Albert Wattenber and Herbert Anderson.

In 1933, Szilárd fled to London to escape Nazi persecution, where he read an article written by Ernest Rutherford in The Times which rejected the possibility of using atomic energy for practical purposes. Although nuclear fission had not yet been discovered, Szilárd was reportedly so annoyed at this dismissal that he conceived of the idea of the nuclear chain reaction while waiting for traffic lights to change on Southampton Row in Bloomsbury. The following year he filed for a patent on the concept.

Szilárd first attempted to create a chain reaction using beryllium and indium, but these elements did not yield such a reaction. In 1936, he assigned the chain-reaction patent to the British Admiralty to ensure its secrecy (GB patent 630726). Szilárd also was the co-holder, with Nobel Laureate Enrico Fermi, of the patent on the nuclear reactor (U.S. Patent 2708656 (PDF)).

In 1938, Szilárd accepted an offer to conduct research at Columbia University in Manhattan, and moved to New York, and was soon joined by Fermi. After learning about nuclear fission in 1939, they concluded that uranium would be the element capable of sustaining a chain reaction. Szilárd and Fermi conducted a simple experiment at Columbia and discovered significant neutron multiplication in uranium, proving that the chain reaction was possible and opening the way to nuclear weapons. Szilárd later described the event: "We turned the switch, saw the flashes, watched for ten minutes, then switched everything off and went home. That night I knew the world was headed for sorrow."[1]

Around that time, the Germans and others were in a race to produce a nuclear chain reaction. German attempts to control the chain reaction sought to do so using graphite, but these attempts proved unsuccessful. Szilárd realized graphite was indeed perfect for controlling chain reactions, just as the Germans had determined, but that the method of producing graphite used boron carbide rods, and the minute amount of boron impurities in the manufactured graphite was enough to stop the chain reaction. Szilárd had graphite manufacturers produce boron-free graphite. As a result, the first human-controlled chain reaction occurred on December 2, 1942.[2]

The Manhattan Project

Szilárd was directly responsible for the initiation of the Manhattan Project. He drafted a confidential letter to Franklin D. Roosevelt (FDR) explaining the possibility of nuclear weapons, warning of Nazi work on such weapons, and encouraging the development of a program that could lead to their creation. In August 1939, he approached his old friend and collaborator Albert Einstein and convinced him to sign the letter, lending the weight of his fame to the proposal.[3]

The Einstein-Szilárd letter led directly to the establishment of research into nuclear fission by the U.S. government and ultimately to the creation of the Manhattan Project. FDR handed the letter off to an aide, General Edwin M. "Pa" Watson with the instruction: "Pa, this requires action!"[4]

Later, Szilárd moved to the University of Chicago to continue work on the project. There, along with Fermi, he helped construct the first "neutronic reactor," a uranium and graphite "atomic pile" in which the first self-sustaining nuclear chain reaction was achieved. On Wednesday, December 2, 1942, at 3:25 p.m., the experiment was run successfully, they were able to control the chain-reaction fission of uranium. The power generated by this very first nuclear reactor was just 40 watts—equivalent to a dim light bulb or a burning match. After just 28 minutes of operation, the reaction was stopped with cadmium strips to mop up the neutrons and quench the chain reaction.

As the war continued, Szilárd became increasingly dismayed that scientists were losing control over their research to the military, and clashed many times with General Leslie Groves, military head of the project. His resentment towards the U.S. government was exacerbated by his failed attempt to avoid the use of the atomic bomb in war.

Szilárd became a naturalized citizen of the United States in 1943.

Views on the use of nuclear weapons

In 1932, Szilárd had read about the fictional "atomic bombs" described in H. G. Wells's science fiction novel The World Set Free. This inspired him to be the first scientist to seriously examine the science behind the creation of nuclear weapons. As a scientist, he was the first person to conceive of a device that, using a nuclear chain reaction as fuel, could be used as a bomb.

As a survivor of a devastated Hungary after World War I, and having witnessed the subsequent terror of the Reds and the Whites, Szilárd developed an enduring passion for the preservation of human life and freedom, especially freedom to communicate ideas.

He hoped that the U.S. government, which prior to World War II had staunchly opposed the bombing of civilians, would not use nuclear weapons because of their potential for use against civilian populations. Szilárd hoped that the mere threat of such weapons would force Germany and/or Japan to surrender. He drafted the Szilárd petition advocating demonstration of the atomic bomb. However, with the European war concluded and the U.S. taking heavy casualties in the Pacific, the new U.S. President Harry Truman sided with advisers and chose to use atomic bombs against Hiroshima and Nagasaki over the protestations of Szilárd and other scientists.

After the war

In 1947, Szilárd switched fields of study because of his horror of atomic weapons, moving from physics to molecular biology, working extensively with Aaron Novick. He proposed, in February of 1950, a new kind of nuclear weapon using cobalt as a tamper, a cobalt bomb, which he said might wipe out all life on the planet. U.S. News & World Report featured an interview with Szilárd in its August 15, 1960 issue, "President Truman Didn't Understand." His penchant to use language provocatively and say things which most readers would dismiss as absurd is well evidenced in this quote from that interview, "But again, I don't believe this staging a demonstration was the real issue, and in a sense it is just as immoral to force a sudden ending of a war by threatening violence as by using violence. My point is that violence would not have been necessary if we had been willing to negotiate."

In 1961, Szilárd published a book of short stories, The Voice of the Dolphins, in which he wrestled with the moral and ethical issues raised by the Cold War and his own role in the development of atomic weapons.

Szilárd married Gertrud Weiss in 1951. He spent his last years as a fellow at the Salk Institute in San Diego.

In 1960, Szilárd was diagnosed with bladder cancer. He underwent radiation therapy at New York's Memorial Hospital using a treatment regimen that he designed himself. A second round of treatment followed in 1962; Szilárd's cancer remained in remission thereafter.

In 1962, Szilárd was part of a group of scientists who founded the Council for a Livable World. The Council's goal was to warn the public and Congress of the threat of nuclear war and lead the way to rational arms control and nuclear disarmament.

In May of 1964, Szilárd died in his sleep of a heart attack at the age of sixty-six. At his memorial, it was said that Death was required to come to him while asleep, or otherwise he would have outwitted it.

Personality and predictive powers

Szilárd was well known to his colleagues as an eccentric, lightning-quick thinker who "seemed fond of startling people" with strange, seemingly incongruous, yet extremely perceptive statements and questions. He was also extremely good at predicting political events. He is said to have predicted World War I as a boy, and when the Nazi party first appeared, he predicted that it would one day control Europe. In 1934, he foresaw the details of World War II. He then made a habit of residing in hotel rooms, with a packed suitcase always on hand.

Memberships and honors

  • American Academy of Arts and Sciences (1954)
  • American Physical Society
  • National Inventors Hall of Fame

Named after him

  • The impact crater Szilárd (34.0°N, 105.7°E, 122km dia.) on the lunar farside is named after him.


  1. Richard Rhodes, The Making Of The Atomic Bomb (New York: Simon & Schuster, 1986). ISBN 0671441337
  2. Hans A. Bethe, The German Uranium Project, Physics Today Online. Retrieved November 9, 2007.
  3. Hyper Text Book, Einstein. Retrieved November 11, 2007.
  4. The Atomic Heritage Foundation, Pa, this requires action! Retrieved November 9, 2007.


  • Asimov, Isaac. 1982. Asimov's Biographical Encyclopedia of Science and Technology. Garden City, NY: Doubleday. ISBN 0385177712
  • Lanouette, William with Bela Silard. 1992. Genius in the Shadows: A Biography of Leo Szilárd: The Man Behind The Bomb. New York: Charles Scribner's Sons. ISBN 0684190117
  • Szilard, Leo, Spencer R. Weart, and Gertrud Weiss Szilard. 1978. Leo Szilard, his Version of the Facts Selected Recollections and Correspondence. Cambridge, Mass: MIT Press. ISBN 0262191687
  • Szilárd, Leo. 1961. The Voice of the Dolphins, and Other Stories. New York: Simon & Schuster. ISBN 0804717540

External links


  • U.S. Patent 2708656 (PDF)Neutronic reactor—E. Fermi, L. Szilárd, filed December 19, 1944, issued May 17, 1955. Retrieved November 9, 2007.
  • U.S. Patent 1781541 (PDF)—Einstein Refrigerator—co-developed with Albert Einstein filed in 1926, issued November 11, 1930. Retrieved November 9, 2007.


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