Szilárd, c. 1960
February 11, 1898|
|Died||May 30, 1964
La Jolla, California, U.S.
|Residence||Hungary, Germany, United States, United Kingdom|
|Institutions||Budapest Technical University
Technical University of Berlin
Humboldt University of Berlin
University of Chicago
|Alma mater||Technische Universität Berlin
Humboldt Universität zu Berlin
|Thesis||Über die thermodynamischen Schwankungserscheinungen (1923)|
|Doctoral advisor||Max von Laue|
|Other academic advisors||Albert Einstein|
|Notable students||Bernard T. Feld
Maurice Sanford Fox
|Known for||Nuclear chain reaction
|Notable awards||Atoms for Peace Award (1959)
Albert Einstein Award (1960)
Leó Szilárd (Hungarian: Szilárd Leó; German: Leo Spitz until age 2; 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 reactor with Enrico Fermi, and in late 1939 wrote the letter for Albert Einstein's signature that resulted in the Manhattan Project that built the atomic bomb.
Leó Spitz was born in Budapest, Hungary, on February 11, 1898. His middle-class parents, both Jewish, Louis Spitz, a civil engineer, and Thekla Vidor, raised Leó on the Városligeti Fasor in Pest, Hungary. He had two younger sibling, a brother, Béla, born in 1900, and a sister, Rózsi (Rose), 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 Magyar. Despite having a religious background, Szilárd became an agnostic. 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 won the Eötvös Prize, a national prize for mathematics.
With the First World War raging in Europe, Szilárd 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 joined his regiment in May 1918, but in September, before his regiment was sent to the front lines, he fell ill with Spanish Influenza, and he was returned home for hospitalization. Later he was informed that his regiment had been nearly annihilated in battle, so the sickness probably saved his life. He was discharged honorably in November 1918, after the end of the war.
In January 1919 Szilárd resumed his engineering his studies, but Hungary was in a chaotic political situation with the rise of the Hungarian Soviet Republic under Béla Kun. Szilárd and his brother Bela founded their own political group, the Hungarian Association of Socialist Students. 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.
Convinced that there was no future for him in Hungary, Szilárd left for Berlin via Austria on December 25, 1919,and enrolled at Technische Hochschule (Institute of Technology) in Berlin-Charlottenburg. He was soon joined by his brother Bela. Szilárd 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. He also met fellow Hungarian students Eugene Wigner, John von Neumann and Dennis Gabor. His doctoral dissertation on thermodynamics Über 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 physicist James Clerk Maxwell. The problem was thought to be insoluble, but in tackling it Szilárd recognized the connection between thermodynamics and Information theory.
Szilárd 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 Szilárd's engine and became important in the history of attempts to understand Maxwell's demon. This paper also is 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 Szilárd's paper as his starting point.
Throughout his time in Berlin, Szilárd worked on numerous technical inventions. For example, in 1928 he submitted a patent application for the linear accelerator,and in 1929 applied for one for the cyclotron, not knowing of Gustav Ising's prior 1924 journal article and Rolf Widerøe's operational device, and also the cyclotron. Between 1926 and 1930, he worked with Einstein to develop the Einstein refrigerator, notable because it had no moving parts. He conceived the linear accelerator in 1928, and also the electron microscope. Szilárd himself 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, Szilárd 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.
Developing the idea of the nuclear chain reaction
When Adolf Hitler became chancellor of Germany in January 20, 1933, Szilárd urged his family and friends to flee Europe while they still could. He moved to England, and transferred his savings of £1,595 from his bank in Zurich to the one in London. He lived in hotels where lodging and meals cost about £5/5 a week. For those less fortunate, he founded 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.
In September 12, 1933, Szilárd read an article in The Times summarizing a speech given by Lord Rutherford in which he rejected the feasibility of using atomic energy for practical purposes. Rutherford's 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. 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. 
Szilárd was so annoyed at Rutherford's dismissal that 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 Szilárd 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. The following year he filed for a patent on the concept of the neutron-induced nuclear chain reaction. Richard Rhodes described Szilárd's moment of inspiration:
In London, where Southampton Row passes Russell Square, across from the British Museum in Bloomsbury, Leo Szilárd 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 Szilárd 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. Szilárd 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 woes, the shape of things to come.
In early 1934 he 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 phenomena known as the Fermi Effect after its discoverer, the Italian physicist Enrico Fermi. When they bombarded ethyl iodide with neutrons produced by a radon-beryllium 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. He also attempted unsuccessfully to create a nuclear chain reaction using beryllium by bombarding it with X-rays. In 1936, Szilárd assigned his chain-reaction patent to the British Admiralty to ensure its secrecy.
Szilárd visited Bela and Rose and her husband, the painter Peter Detre, in Switzerland in September 1937. After a rainstorm, he and his siblings spent an afternoon in an unsuccessful attempt to build a prototype collapsible umbrella. One reason for the visit was that he had decided to emigrate to the United States, as he had decided that another war in Europe was inevitable and imminent. He reached New York on the liner RMS Franconia on January 2, 1938. He conducted experiments with indium at the University of Rochester, but again failed to initiate a chain reaction.
In November 1938, Szilárd moved to New York City, taking a room at the King's Crown Hotel near Columbia University. He encountered John R. Dunning, who invited him to speak about his research at an afternoon seminar in January 1939. That month, Neils Bohr brought news to New York of the discovery of nuclear fission in Germany by Otto Hahn and Fritz Strassmann, and its theoretical explanation by Lise Meitner, and Otto Frisch. When Szilárd found out about it on a visit to Wigner at Princeton University, he immediately realised that uranium might be the element capable of sustaining a chain reaction.
Unable to convince Fermi that this was the case, Szilárd set out on his own. He obtained permission from the head of the Physics Department at Columbia, George Pegram, to use a laboratory for three months. To fund his experiment, he borrowed $2,000 from a fellow inventor, Benjamin Liebowitz. He wired Frederick Lindemann at Oxford and asked him to send a beryllium cylinder. He convinced Walter Zinn to become his collaborator, and hired Semyon Krewer to investigate processes for manufacturing pure uranium and graphite.
Szilárd and Zinn conducted a simple experiment on the seventh floor of Pupin Hall at Columbia, using a radium-beryllium source to vombard uranium with neutrons. Initially nothing registered on the oscilloscope, but then Zinn realised that it was not plugged in. On doing so, they discovered significant neutron multiplication in natural uranium, proving that a chain reaction might be possible. Szilárd later described the event: "We turned the switch and saw the flashes. We watched them for a little while and then we switched everything off and went home". He understood the implications and consequences of this discovery, though. "That night, there was very little doubt in my mind that the world was headed for grief".
While they had demonstrated that the fission of uranium produced produced more neutrons than it consumed, this was still not a chain reaction. Szilárd persuaded Fermi and Herbert L. Anderson to try a larger experiment using 500 pounds (230 kg) of uranium. To maximise the chance of fission, they needed a neutron moderator to slow the neutrons down. Hydrogen was a known moderator, so they used water. The results were disappointing. It became apparent that hydrogen slowed neutrons down, but also absorbed them, leaving fewer for the chain reaction. Szilárd then suggested Fermi use carbon, in the form of graphite. He felt he would need about 50 tonnes (49 long tons; 55 short tons) of graphite and 5 tonnes (4.9 long tons; 5.5 short tons) of uranium. As a back-up plan, Szilárd also considered where he might find a few tons of heavy water; deuterium would not absorb neutrons like ordinary hydrogen, but would have the similar value as a moderator. Such quantities of materiel would require a lot of money, 
Szilárd drafted a confidential letter to the President, Franklin D. Roosevelt, explaining the possibility of nuclear weapons, warning of Nazi work on such weapons and encouraging the development of a program which could result in their creation. With the help of Wigner and Edward Teller,he approached his old friend and collaborator Einstein in August 1939, and convinced him to sign the letter, lending his fame to the proposal. The Einstein–Szilárd letter resulted in the establishment of research into nuclear fission by the U.S. government, and ultimately to the creation of the Manhattan Project. Roosevelt gave the letter to his aide, Brigadier General Edwin M. "Pa" Watson with the instruction: "Pa, this requires action!"
An Advisory Committee on Uranium was formed under Lyman J. Briggs, a scientist and the director of the National Bureau of Standards. Its first meeting on October 21, 1939, was attended by Szilárd, Teller and Wigner, who persuaded the Army and Navy to provide $6,000 for Szilárd to purchase supplies for experiments, in particular, more graphite. Fermi and Szilárd met with representatives National Carbon Company, who manufactured graphite, where Szilárd made another important discovery. By quizzing them about impurities in their graphite, he found that it contained boron, a neutron absorber. He then had graphite manufacturers produce boron-free graphite. Had he not done so, they might have concluded, as the German nuclear energy project did, that graphite was unsuitable for use as a neutron moderator. Like the German project, Fermi and Szilárd still believed that enormous quantities of uranium would be required for an atomic bomb, and therefore concentrated on producing a controlled chain reaction. Fermi determined that fissioning uranium atom produced 1.73 neutrons on average. It was enough, but a careful design was call for to minimize losses. Szilárd worked up various designs for a nuclear reactor. "If the uranium project could have been run on ideas alone," Wigner later remarked, "no one but Leo Szilárd would have been needed."
The December 6, 1941, meeting of the National Defense Research Committee resolved to proceed with an all-out effort to produce atomic bomvs, a decision given urgency by the Japanese attack on Pearl Harbor the following day that brought the United States into World War II, and the then formal approval by Roosevelt in January 1942. Arthur H. Compton from the University of Chicago was appointed head of research and development. Against Szilárd's wishes, Compton concentrated all the groups working on reactors and plutonium at the Metallurgical Laboratory at the University of Chicago. Compton laid out an ambitious plan to achieve a chain reaction by January 1943, start manufacturing plutonium in nuclear reactors by January 1944, and to produce an atomic bomb by January 1945.
Szilárd moved to Chicago in January 1942, where he became a research associate, and later the chief physicist, at the Metallurgical Laboratory. There, along with Fermi, he helped to construct the first "neutronic reactor", a uranium and graphite "atomic pile" in which the first self-sustaining nuclear chain reaction was achieved in 1942. Szilárd also was the co-holder, with Nobel Laureate Enrico Fermi, of the patent on the nuclear reactor.
As the war continued, Szilárd became increasingly dismayed that scientists were losing control of their research to the military, and argued many times with General Leslie Groves, military director of the project. His resentment towards the U.S. government was exacerbated by his failure to prevent the destructive use of the atomic bomb through having a test explosion that could be witnessed by Japanese observers who would then have the opportunity to surrender and spare lives.
Szilárd became a naturalized citizen of the United States in 1943.
Szilárd had an enduring passion for the preservation of human life and political freedom, especially freedom to communicate ideas. He hoped that the U.S. government 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 also worried about the long term implications of the usage of nuclear weapons, predicting that their usage by the United States would start a nuclear arms race with Russia. He drafted the Szilárd petition advocating demonstration of the atomic bomb. However with the European war concluded and the U.S. suffering many casualties in the Pacific Ocean region, the new U.S. President Harry Truman agreed 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 shifted his field of study from nuclear physics to biophysics and molecular biology, working extensively with Aaron Novick. The change is widely credited as Szilárd's zero interest to support the development of stronger nuclear weapons.
Szilárd married Gertrud Weiss in 1951.
Szilárd as both nuclear and bio physicist understood very exactly how radiation harms the life. In February 1950 he publicly alerted against the developed salted bombs, explaining in radio talk, that a cobalt bomb, a new kind of nuclear weapon using cobalt as a tamper, might destroy all life on the planet. In his new field, biophysics, he gave essential advice to Theodore Puck and Philip I. Marcus for their first cloning of a human cell in 1955.
U.S. News & World Report featured an interview with Szilárd in its August 15, 1960 issue, "President Truman Didn't Understand." Szilard argued against bombing of Hiroshima and Nagasaki 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 dealt with the moral and ethical issues raised by the Cold War and his own role in the development of atomic weapons. The title story described an international biology research laboratory in Central Europe. This became reality after a meeting in 1962 with Victor F. Weisskopf, James Watson and John Kendrew. When the European Molecular Biology Laboratory was established, the library was named The Szilárd Library and the library stamp features dolphins.
In 1960, Szilárd was diagnosed with bladder cancer. He underwent cobalt therapy at New York's Memorial Sloan-Kettering Hospital using a cobalt 60 treatment regimen that he designed himself. He knew the properties of this isotope also from his estimates about the salted bombs with cobalt. A second round of treatment with an increased dose followed in 1962. The doctors tried to tell him that the increased radiation dose would kill him, but he said it wouldn't, and that anyway he would die without it. The higher dose did its job and his cancer never returned. This treatment became standard for many cancers and is still used.
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 encourage rational arms control and nuclear disarmament.
In February 2014, the UCSD Library announced that they received grant funding from the National Historical Publications and Records Commission (NHPRC) to digitize its collection of Szilard's papers, extending from 1938 - 1998.
- American Academy of Arts and Sciences 1954
- American Physical Society
- Atoms for Peace Award 1959
- National Inventors Hall of Fame
- Humanist of the Year 1960
- The crater Szilárd (34.0°N, 105.7°E, 122 km dia.) on the far side of the Moon is named after him.
- GB 630726 —Improvements in or relating to the transmutation of chemical elements—L. Szilárd, filed June 28, 1934
- U.S. Patent 2,708,656—Neutronic reactor—E. Fermi, L. Szilárd, filed December 19, 1944, issued May 17, 1955
- U.S. Patent 1,781,541—Einstein Refrigerator—co-developed with Albert Einstein filed in 1926, issued November 11, 1930
- see Szilárd's patent specification 1934
- Lanouette & Silard 1992, pp. 10-13.
- Lanouette & Silard 1992, pp. 13-15.
- Lanouette & Silard 1992, p. 167.
- Byers, Nina. "Fermi and Szilard". Retrieved May 23, 2015.
- Frank 2008, pp. 244-246.
- Blumesberger, Doppelhofer & Mauthe 2002, p. 1355.
- Lanouette & Silard 1992, pp. 36-41.
- Bess 1993, p. 44.
- Lanouette & Silard 1992, p. 42.
- Lanouette & Silard 1992, pp. 44-49.
- Lanouette & Silard 1992, pp. 49-52.
- Lanouette & Silard 1992, pp. 56-58.
- Hargittai 2006, p. 44.
- Szilard, Leo (December 1, 1925). "Über die Ausdehnung der phänomenologischen Thermodynamik auf die Schwankungserscheinungen". Zeitschrift für Physik (in German) 32 (1): 753–788. doi:10.1007/BF01331713. ISSN 0044-3328.
- Lanouette & Silard 1992, pp. 60-61.
- Szilárd, Leo (1929). "Über die Entropieverminderung in einem thermodynamischen System bei Eingriffen intelligenter Wesen". Zeitschrift für Physik (in German) 53 (11-12). pp. 840–856. doi:10.1007/BF01341281. ISSN 0044-3328. Available on-line in English at: Aurellen.org.
- Lanouette & Silard 1992, pp. 62-65.
- Lanouette & Silard 1992, pp. 101-102.
- U.S. Patent 1,781,541
- Telegdi, V. L. (2000). "Szilard as Inventor: Accelerators and More". Physics Today 53 (10): 25. Bibcode:2000PhT....53j..25T. doi:10.1063/1.1325189.
- Calaprice & Lipscombe 2005, p. 110.
- Lanouette & Silard 1992, pp. 83-85.
- Dannen, Gene (1998). "Leo Szilard the Inventor: A Slideshow". Budapest. Retrieved May 24, 2015.
- Rhodes 1986, p. 26.
- Lanouette & Silard 1992, pp. 119-122.
- Lanouette & Silard 1992, pp. 131-132.
- Rhodes 1986, p. 27.
- GB 630726
- Lanouette & Silard 1992, pp. 133-135.
- Rhodes 1986, pp. 292-293.
- Chalmers, T. A. (September 22, 1934). "Chemical Separation of the Radioactive Element from its Bombarded Isotope in the Fermi Effect". Nature 134: 462. doi:10.1038/134462b0. ISSN 0028-0836.
- Chalmers, T. A. (September 29, 1934). "Detection of Neutrons Liberated from Beryllium by Gamma Rays: a New Technique for Inducing Radioactivity". Nature 134: 494–495. doi:10.1038/134494b0. ISSN 0028-0836.
- Lanouette & Silard 1992, pp. 145-148.
- Lanouette & Silard 1992, p. 148.
- Brasch, A.; Lange, F.; Waly, A.; Banks, T. E.; Chalmers, T. A.; Szilard, Leo; Hopwood, F. L. (December 8, 1934). "Liberation of Neutrons from Beryllium by X-Rays: Radioactivity Induced by Means of Electron Tubes". Nature 134: 880. doi:10.1038/134880a0. ISSN 0028-0836.
- Rhodes 1986, pp. 224-225.
- Lanouette & Silard 1992, pp. 166-167.
- Lanouette & Silard 1992, pp. 172-173.
- Lanouette & Silard 1992, pp. 178-179.
- Lanouette & Silard 1992, pp. 182-183.
- Lanouette & Silard 1992, pp. 186-187.
- Rhodes 1986, p. 291.
- Rhodes 1986, p. 292.
- Lanouette & Silard 1992, pp. 194-195.
- The Atomic Heritage Foundation. "Einstein's Letter to Franklin D. Roosevelt". Retrieved May 26, 2007.
- The Atomic Heritage Foundation. "Pa, this requires action!". Retrieved May 26, 2007.
- Hewlett & Anderson 1962, pp. 19-21.
- Lanouette & Silard 1992, p. 222.
- Bethe, Hans A. (March 27, 2000). "The German Uranium Project". Physics Today Online 53 (7): 34. Bibcode:2000PhT....53g..34B. doi:10.1063/1.1292473.
- Lanouette & Silard 1992, p. 227.
- Hewlett & Anderson 1962, p. 28.
- Lanouette & Silard 1992, pp. 227-231.
- U.S. Patent 2,708,656)
- Jacob Bronowski (writer, presenter). "Knowledge or Certainty". The Ascent of Man. 41:14 minutes in.
- Esterer & Esterer (1972:148).
- "Brief History". European Molecular Biology Laboratory. Retrieved February 22, 2011.
- "Szilárd Library". European Molecular Biology Laboratory. Retrieved February 22, 2011.
- Tech, Motley. "The man who changed war, peace and the world". Retrieved 1 May 2015.
- Dolores Davies. "Materials Documenting Birth of Nuclear Age to be Digitized".
- Bess, Michael (1993). Realism, Utopia, and the Mushroom Cloud: Four Activist Intellectuals and their Strategies for Peace, 1945-1989. Chicago: University of Chicago Press. ISBN 0-226-04421-1. OCLC 27894840.
- Blumesberger, Susanne; Doppelhofer, Michael; Mauthe, Gabriele (2002). Handbuch österreichischer Autorinnen und Autoren jüdischer Herkunft 1. Munich: K. G. Saur. ISBN 9783598115455. OCLC 49635343.
- Calaprice, Alice; Lipscombe, Trevor (2005). Albert Einstein: A Biography. Westport, Connecticut: Greenwood Press. ISBN 978-0-313-33080-3. OCLC 57208188.
- Frank, Tibor (2008). Double exile: migrations of Jewish-Hungarian professionals through Germany to the United States, 1919-1945. Exile Studies 7. Oxford: Peter Lang. ISBN 3-03911-331-3. OCLC 299281775.
- Hargittai, István (2006). The Martians of Science: Five Physicists Who Changed the Twentieth Century. Oxford: Oxford University Press. ISBN 978-0-19-517845-6. OCLC 62084304.
- Hewlett, Richard G.; Anderson, Oscar E. (1962). The New World, 1939–1946 (PDF). University Park: Pennsylvania State University Press. ISBN 0-520-07186-7. OCLC 637004643. Retrieved 26 March 2013.
- Lanouette, William; Silard, Bela (1992). Genius in the Shadows: A Biography of Leo Szilárd: The Man Behind The Bomb. New York: Skyhorse Publishing. ISBN 1-626-36023-5. OCLC 25508555.
- Rhodes, Richard (1986). The Making of the Atomic Bomb. New York: Simon and Schuster. ISBN 0671441337. OCLC 25508555.
- Esterer, Arnulf K.; Esterer, Luise A. (1972). Prophet of the Atomic Age: Leo Szilárd. New York: Julian Messner. ISBN 0-671-32523-X. OCLC 1488166.
- Szilárd, Leo; Weiss-Szilárd, Gertrud; Weart, Spencer R. (1978). Leo Szilárd: His Version of the Facts : Selected Recollections and Correspondence. Cambridge, Massachusetts: The MIT Press. ISBN 0-262-69070-5. OCLC 4037084.
- Szilárd, Leo (1992). The Voice of the Dolphins: And Other Stories (Expanded edition from 1961 original ed.). Stanford, CA.: Stanford University Press. ISBN 0-8047-1754-0. OCLC 758259818.
|Wikimedia Commons has media related to Leo Szilard.|
|Wikiquote has quotations related to: Leó Szilárd|
- Leo Szilárd Online—an "Internet Historic Site" (first created March 30, 1995) maintained by Gene Dannen
- Leo Szilárd's page at atomicarchive.com
- Register of the Leo Szilard Papers, 1898-1998, Mandeville Special Collections, UC San Diego Library
- Einstein's Letter to President Roosevelt—1939
- Annotated bibliography for Leo Szilárd from the Alsos Digital Library
- Szilárd biography at Hungary.hu
- The Szilárd Library at the European Molecular Biology Laboratory
- Szilárd lecture on war
- Szilárd's math genealogy