Leó Szilárd, the man with great ideas on nuclear physics, engineering and molecular biology

Leó Szilárd

February 11, 1898, in Budapest (Hungary) – May 30, 1964, in La Jolla, California (United States)

He was born into a middle-class family of Jewish origin in Budapest under the German surname “Spitz” which they changed in 1900 to the Hungarian “Szilzárd”, which means “solid”.

From 1908 to 1916, he attended the “Reáliskola” secondary school in his hometown, showing an interest in physics and a great ability in mathematics that led him to win, in 1916, the Eötvös National Prize for Mathematics. That same year, he was drafted into the army and enrolled in engineering at the Budapest University of Technology and Economics.

In 1918, before he was sent to the front lines, he fell ill with the flu pandemic and returned home to be hospitalized. He was honorably discharged later that year, after the war ended.

In 1919, Szilárd resumed his engineering studies, although Hungary was in a chaotic political situation so convinced that there was no future for him in Hungary, he traveled to Berlin and enrolled at the Technische Hochschule (Technical University) in Berlin. However, he lost interest in engineering and his attention turned to physics. This discipline was not taught at his university so he transferred to the Guillermo Federico University, where he attended lectures by Albert Einstein, Max Planck, Walther Nernst, James Franck and Max von Laue.

His publications on the ancient philosophy problem of thermal and statistical physics, known as Maxwell's Demon (James Clerk Maxwell), was praised by Einstein and won top honors in 1922. It was thought to be unsolvable, but when tackled, Szilárd recognized the connection between thermodynamics and information theory and introduced the experiment known as the Szilárd machine.

In 1924, Szilárd was appointed assistant to Max von Laue at the Institute for Theoretical Physics and in 1927 he became professor of physics..

Unrecognized discoveries

While in Berlin in 1928, he filed a patent application for a linear accelerator unaware of the existence of a previous article by Gustav Ising in a magazine in 1924, nor of the operating device by Rolf Widerøe, in 1929 he applied for a patent for the cyclotron, conceived an electron microscope, and between 1926 and 1930, worked with Einstein to develop a static refrigerator (it had no moving parts).

He did not build any of these devices or publish these ideas in scientific journals, so the credit went to others. As a result, Szilárd never received the Nobel Prize, but Ernest Lawrence was awarded for the cyclotron in 1939 and Ernst Ruska for the electron microscope in 1986.

Your humanitarian work

Nacionalidad alemana Leó Szilárd

In 1930, he received German citizenship but no longer agreed with the political situation in Europe, and in 1933, when Adolf Hitler became Chancellor of Germany, he urged his family and friends to flee Europe while they still could.

He emigrated to England, helping to found the Academic Assistance Council, an organization dedicated to helping refugee scholars find new jobs, and convening the Royal Society to provide lodgings at Burlington House. By the outbreak of World War II in 1939, she had helped more than 2,500 refugee students find employment.

Idea of nuclear chain reaction

On September 12, 1933, in London, Szilárd read an article in "The Times" that summarized a speech given by Ernest Rutherford that rejected the feasibility of using atomic energy for practical purposes, saying that it was a very poor and inefficient way of produce energy and anyone looking for a source of energy in the transformation of atoms was talking about "moonshine". The speech specifically referred to recent work by his students John Cockcroft and Ernest Walton "splitting lithium into alpha particles by bombarding it with protons from a particle accelerator they had built."

According to Szilárd, he was so angry with Rutherford for not wanting to talk about nuclear energy that while waiting to cross Southhampton Avenue in Bloomsbury, he conceived the idea of a nuclear chain reaction, using newly discovered neutrons.

The idea wasn't based on nuclear fission because it hadn't been discovered yet, but Szilard realized that if neutrons could start some kind of energy-producing nuclear reaction, like the one that had occurred in lithium, they could be produced. by themselves and, in addition, energy could be obtained with little input, since the reaction would be self-sustaining. He applied for a patent on the neutron-induced nuclear chain reaction concept in 1933, which was granted in 1936.

His interest in radioactive isotopes for medical purposes

In early 1934, Szilard began working at St Bartholomew's Hospital in London along with a physicist on the hospital staff, Thomas A. Chalmers, where he studied radioactive isotopes for medical purposes.

It was known that bombarding elements with neutrons could produce heavier isotopes of an element or a heavier element, a phenomenon known as the Fermi effect after its discoverer. So when they bombarded ethyl iodide with neutrons produced by a radon-beryllium source, they found that the heavier radioactive isotopes of iodine had separated from the compound. Thus, they had discovered a means of separating isotopes. This method became known as the Szilard-Chalmers effect and was widely used in the preparation of medical isotopes.

He also tried unsuccessfully to create a nuclear chain reaction using beryllium by x-ray bombardment, but did not get the reaction he expected and, in 1936, he gave the patent to the British Admiralty to ensure its secrecy. Consequently, his patent was not issued until 1949.

From theory to practice: self-sustaining nuclear chain reaction

In 1938, he accepted an offer to direct research at Columbia University in Manhattan, and moved to New York. At the same time Niels Bohr brought news 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, he immediately realized that uranium could be the element capable of sustaining a chain reaction.

Unable to convince Enrico Fermi that this was the case, Szilard obtained permission from the head of Columbia's Physics Department, George B. Pegram, to use a laboratory for three months, borrowing $2,000 from fellow inventor Benjamin Liebowitz. to finance the experiment, he telegraphed Frederick Lindemann for a cylinder of beryllium and persuaded Walter Zinn to become his collaborator and hired Semyon Krewer to investigate the processes of making pure uranium and graphite.

Szilard and Zinn carried out a simple experiment on the seventh floor of Pupin Hall in Columbia, using a radium-beryllium source to bombard uranium with neutrons. They discovered a significant multiplication of neutrons in natural uranium, showing that a chain reaction could be possible.

Enrico Fermi y Leó Szilárd

Although they had shown that the fission of uranium produced more neutrons than it consumed, this was still not a chain reaction. Szilard persuaded Fermi and Herbert L. Anderson to try a larger experiment using 500 pounds (230 kg) of uranium and to maximize the chance of fission, they needed a neutron moderator to slow down the neutrons, hydrogen.

The results were disappointing. It became clear that the hydrogen slowed down the neutrons, but also absorbed them, leaving less for the chain reaction. Szilard suggested that Fermi use 50 tons of carbon in the form of graphite and 5 tons of uranium and deuterium (heavy water) as a moderator because it would not absorb as many neutrons as hydrogen. Such amounts of material would require a lot of money.

Leó Szilárd y Albert Einstein

A letter drafted by Szilárd and also signed by Albert Einstein to President Franklin D. Roosevelt warning of a German nuclear weapons project led to government interest in nuclear fission research and ultimately the creation of the Manhattan Project.

Looking for suppliers of graphite, Fermi and Slizárd met with representatives of the National Carbon Company and made an important discovery. Szilárd asked about impurities in graphite and the answer was that it usually contained boron, a neutron absorber. He made the proposal that they supply pure graphite without boron.

Fermi determined that a fissioning uranium atom produced 1.73 neutrons on average. It was enough, but careful design was required to minimize losses. Szilard drew up several designs for a nuclear reactor.

In January 1942, Szilard joined the Chicago Metallurgical Laboratory as a research associate and later as chief physicist. He provided important information that while uranium-238 did not fission easily with slow and moderate neutrons, it could still fission with the fast neutrons produced by fission. This effect was small but crucial. Szilard made suggestions to improve the uranium placement and containment process and worked with David Gurinsky and Ed Creutz on a method of recovering uranium from its salts.

An important issue was the cooling of the reactor. Considering that as many neutrons as possible must be conserved, they conducted experiments with bismuth, helium, but in the end, the best option was water.

Szilard was present on December 2, 1942, when the first artificial self-sustaining nuclear chain reaction was achieved at the first nuclear reactor under the Stagg Field overlooks, the Chicago Pile-1.

He was co-owner, along with Enrico Fermi, of the patent on the nuclear reactor. In the end he sold his patent to the government for reimbursement of his expenses, some $15,416, plus the standard fee of $1. He continued to work on the design of nuclear reactors, and is credited with coining the term "breeder reactor." .

Szilárd luchando contra los fines bélicos

In 1943, he became a US citizen, but the war continued and his resentment towards the US government grew due to its failed attempt to prevent the use of the atomic bomb in the war.

This led him to re-investigate a biology and social sciences that he had left in 1933. In 1946, he obtained a research chair at the University of Chicago and became associated with Aaron Novick, a chemist who had worked at the Metallurgical Laboratory for war. They both invented the chemostat, developed methods to measure the growth rate of bacteria, and discovered feedback inhibition, an important factor in processes such as growth and metabolism. In addition, Szilárd made a great contribution to the scientists who carried out the first cloning of a human cell in 1955.

Diagnosed with bladder cancer in 1960, he underwent a cobalt-60 treatment he had designed and was cured.

He helped found the Salk Institute for Biological Studies in La Jolla, San Diego, and the Council for the Livable World in 1962 to deliver "the sweet voice of reason" about nuclear weapons to Congress, the White House, and the United States. American public.

He died in his sleep of a heart attack in 1964.

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