Leo Szilard

• Born: February 11, 1898
• Birthplace: Budapest, Austro-Hungarian Empire (now in Hungary)
• Died: May 30, 1964
• Place of death: La Jolla, California

Hungarian American nuclear physicist

Szilard conceived the chain reaction necessary for a nuclear reactor or an atomic bomb. Szilard was a contributor to the Manhattan Project, which produced the first atomic bombs, used to end World War II.

Primary field: Physics

Primary inventions: Nuclear chain reaction; atomic bomb

Early Life

Leo Szilard (LEH-oh SEE-lahrd) was born to Louis and Tekla Spitz, a Hungarian Jewish couple. They changed their last name in 1900 to Szilard, meaning “solid,” because of governmental pressure to change foreign-sounding names. Leo had a brother, Bela Szilard (later to be known as Bela Silard) and a sister, Rose Szilard. Since their father, Louis, was an engineer, the boys received solid training in mathematics and the sciences. Leo Szilard attended what would become the Budapest Technical University. During World War I, he was drafted into the army. As a college student, he was trained as an officer but was at home, sick with the Spanish flu, when his unit was sent to the front and demolished. The war ended before he recovered.

In 1919, Szilard went to Berlin to study electrical engineering but found physics so intriguing that he began to work toward a doctorate with Max von Laue. Although it was not the problem that he was assigned, Szilard worked out the mathematical proof that Maxwell’s demon could not violate the second law of thermodynamics. One outcome of the second law is that it is impossible to create a perpetual motion machine. Maxwell’s demon had to have knowledge (a “bit” of information) of the particles to sort them. This extra information would allow the sorting of particles. Szilard proved that because the information cannot be known, Maxwell’s demon cannot generate a perpetual motion machine. This proof earned him a doctoral degree and was the cornerstone to the field of information theory that developed later.

Szilard became von Laue’s assistant and later an assistant professor at the University of Berlin. During this time Szilard collaborated with Albert Einstein to invent a refrigerator with no moving parts. Although in seven years they designed three different types of refrigerators and received several patents, none of the refrigerators made it into public use. From this work, however, did come the Einstein-Szilard electromagnetic pump. The pump had no moving parts but instead used an electromagnetic field to push a liquid metal. In 1933, Szilard fled Nazism and Berlin for Vienna and then England. In 1937, he moved permanently to the United States.

Life’s Work

In 1933, Szilard conceived of the concept of a nuclear chain reaction. His thoughts were that it would produce the power needed for the modern world. He first considered beryllium and actually tested it and a few other elements to see if they would produce the chain reaction. In 1939, Szilard thought uranium would produce such a reaction after he heard of the fission of uranium reported by Otto Hahn, Fritz Strassman, and Lise Meitner. After testing the idea and hearing of the work by German scientists, he convinced Einstein to sign a letter that he wrote to President Franklin D. Roosevelt warning the president that German scientists were doing experiments that could lead to making a bomb of dramatic proportion. The letter resulted in a committee being formed and eventually the start of the Manhattan Project to build a bomb.

Szilard worked with Enrico Fermi in building the first nuclear reactor, which proved the concept of nuclear chain reaction. He was the person who arranged for boron-free graphite to be used as a component of the reactor. Normal graphite contains boron, which absorbs neutrons and slows the chain reaction. He continued to contribute to the Manhattan Project until the atomic bombs were completed.

After Germany surrendered, Szilard did not want the bomb to be dropped on Japan. He felt that a demonstration of its power would be enough. After the war, he worked for peace. He had always feared the power of nuclear weapons. He even tried to start peace talks with the Soviet Union. He wrote books such as How to Live with the Bomb and Survive (1960) and The Voice of the Dolphin (1961), a science-fiction look at how dangerous nuclear weapons can be. Szilard also began to work in 1946 on antibodies and on the regulation of enzymes.

On October 13, 1951, he married Gertrud “Trude” Weiss; however, they did not live together until his health began to fail in 1959. Szilard had met the Viennese woman in 1929 and was her mentor and longtime friend. He suggested that she attend medical school because he thought that she was, in his words, too dumb to be a physicist. They had traveled together in England in 1936 and several times in the United States. In the years before their marriage, he had often visited Trude. She worked as a medical doctor in New York, and after 1950, she taught at the University of Colorado Medical School. When Szilard was stricken with bladder cancer in 1959, he arranged for a new type of radiation treatment with Trude as his doctor. The radiation treatment was successful. In February, 1964, they moved to La Jolla, California, for Szilard to take a position at the Salk Institute. He died May 30, 1964, in his sleep, of a heart attack.

Szilard was a brilliant man who enjoyed exchanging ideas with others more than he enjoyed mundane everyday research. He knew how to do research but he wanted to supply the idea and sometimes the advice, yet have someone else do the day-to-day routine work. He liked to sit for hours in a bathtub, where he did some of his best work. His work schedule, or in some views, lack of work schedule, often meant that he had difficulty holding a paying position that offered the freedom that he wanted. His desire was to be able to travel to talk with other scientists. His position at the Salk Institute was his dream job.

The list of ideas that Szilard had is astounding. In 1923, he designed an X-ray sensor element. He next developed an improvement for mercury-vapor lamps for which the Siemens Company bought the licenses. In 1928, he patented a linear accelerator, independent of the design of Rolf Wideroe. A year before Ernest Lawrence built his cyclotron in 1929, Szilard patented a cyclotron and a betatron. All modern accelerators except for electrostatic machines are based on a combination of several ideas: multiple acceleration, focusing, frequency modulation, and phase stability. All of these were theories conceived by Szilard between 1928 and 1934. He also foresaw the electron microscope by 1928. While Szilard was in Berlin (1920-1933), he was granted thirty-one patents. The only patent that actually came to fruition was the “Discharge Tube to Be Used as an Electron Source.” Szilard and Einstein designed and received several patents for three types of refrigerators: absorption, diffusion, and electromagnetic. The most successful idea in terms of use of the early collaboration of Szilard and Einstein was the Einstein-Szilard pump. Its inherent safety makes it valuable in cooling breeder reactors. In 1933, he conceived his most famous idea, the nuclear chain reaction. Shortly afterward, he worked with Thomas Chalmers using a neutron source to irradiate different samples. The results from this work became known as the Szilard-Chalmers reactions, or hot atom chemistry. His work with Chalmers allowed him to eliminate beryllium and a few other elements as chain reaction candidates. In 1935, Szilard conducted a series of experiments on slow neutron absorption that proved him to be competent as a nuclear physicist. In 1939, he went to Columbia and worked with Walter Zinn to prove that neutron-induced fission of uranium did produce enough product neutrons, at least two, to make a chain reaction possible. Szilard and Fermi designed and helped build the first nuclear reactor. Szilard later designed a breeder reactor that would produce plutonium 239. Plutonium 239 could also be used to produce a nuclear chain reaction.

Impact

Without Szilard, the world might not have nuclear power. In the United States, 20 percent of all electricity is generated by nuclear power plants. In other countries, the use of nuclear power is even greater, producing 70 percent of the electricity for France. One-third of the electricity for Belgium, Sweden, Spain, and Switzerland is from nuclear power.

The breeder reactor is used more in other countries than in the United States. The breeder reactor produces new fuel for the next round of energy production while making energy to produce electricity. It uses the neutrons from the fissioning of uranium 235 to change uranium 238 to plutonium 239. This method was used to produce the plutonium for the atomic bomb tested at White Sands, New Mexico, and the atomic bomb dropped on Nagasaki, Japan.

Bibliography

Hawkins, Helen, G. Allen Greb, and Gertrud Weiss Szilard, eds. Toward a Livable World. Cambridge, Mass.: MIT Press. 1987. Begins with a biography of Szilard and covers the work toward world peace that Szilard did in his last twenty years. In particular, it contains his views about the danger of nuclear weapons. Bibliography, index.

Lanouette, William. Genius in the Shadows: A Biography of Leo Szilard. New York: Charles Scribner’s Sons, 1992. This well-annotated text completed with the help of Szilard’s brother, Bela Silard, includes information from many of the letters between the brothers. It is an outstanding chronological history of Szilard’s life and how the ideas that he had affected his life. Pictures, bibliography, index.

‗‗‗‗‗‗‗. “The Odd Couple and the Bomb.” Scientific American 283, no. 5 (November, 2000): 104-109. The story of two larger-than-life figures who did not get along, had trouble working together, and knew that they had to make it work. Enrico Fermi, the Italian physicist, and Szilard, the Hungarian physicist, designed and helped build the first nuclear reactor. Both were instrumental in building the atomic bomb. Pictures, bibliography.

Telegdi, Valentine L. “Szilard as Inventor: Accelerators and More.” Physics Today 53, no. 10 (October, 2000): 25-28. The article focuses on Szilard as an inventor, especially of the accelerator. Although Szilard did not build an accelerator, he did design and apply for patents for several accelerators and for devices that are part of an accelerator. Illustrations, bibliography.

Weart, Spencer R., and Gertrud Weiss Szilard, eds. Leo Szilard: His Version of the Facts. Cambridge, Mass.: MIT Press, 1980. These selected recollections and correspondence compiled by Spencer Weart and Szilard’s wife present Szilard’s view of his world. Footnotes, index.