Lev Kowarski

Lew Kowarski in Montreal in 1942

Lew Kowarski ( Russian Лев Николаевич Коварский ; born February 10 ^{. Jul} / 23. February  1907 ^greg. In Saint Petersburg , † the 30th July 1979 in Geneva ) was a Russian-French physicist . Kowarski was a pioneer in nuclear physics and did significant work on the nuclear chain reaction.

life and work

Lev Kowarski was born in St. Petersburg, the Russian capital at the time, as the son of the Jewish merchant Nikolaus Kowarski and the Ukrainian singer Olga V Klassenko. He first spent his childhood in his hometown. After the Bolsheviks came to power , however, the family fled west and Kowarski, as a 12-year-old, was smuggled westwards through the demobilizing German front lines under adventurous circumstances in 1919. He settled with his father in Vilnius and attended school there (the city was separated from Poland in 1920have been incorporated). During his youth he proved to be a talented musician, but had to give up the idea of ​​a career as a musician when it became clear that his fingers were too thick for the keyboard . Still supported with small sums of money by his father, he studied chemical engineering in Brussels and Lyon. He received his diploma in Lyon in 1928 and then began postgraduate studies in chemistry and physics at the University of Paris. He financed his living in Paris by working in a factory in which gas piping systems were constructed. In 1931 he began to write a dissertation on a crystallographic topic in the laboratory of Jean-Baptiste Perrin . This brought him into contact with the Joliot-Curie family of scientists ( Marie Curie , her daughter Irène Joliot-Curie and her husband Frédéric Joliot ). The Joliot-Curie couple received the Nobel Prize in Chemistry in 1935 for their work in the field of artificial radioactivity. In the same year, Joliot received a professorship at the Collège de France and Kowarski got a low-paid job as Joliot's secretary. When Kowarski also received a research grant, he had finally achieved the financial independence that enabled him to quit working in the gas pipe factory.

After the results of Otto Hahn and Fritz Straßmann on uranium nuclear fission in Berlin and its correct interpretation by Lise Meitner and her nephew Otto Frisch in the Paris laboratory at the beginning of 1939 , Joliot was immediately aware of its great importance. The Paris group, consisting of Frédéric Joliot, the German émigré Hans von Halban and Lew Kowarski set about reproducing the experiments of Hahn and Straßmann. Within a very short time it became clear to them that ²³⁵ uranium could be split by bombardment with slow ("thermal") neutrons and that further neutrons were released during the splitting, which could trigger a chain reaction. In April 1939 the Paris working group found that the fission of ²³⁵ U released an average of 3.7 neutrons (the exact value is 2.5 neutrons). The result was published despite the fact that Leó Szilárd and Victor Weisskopf at Princeton had strongly advised their physicists (and all other laboratories outside Germany that dealt with these questions) not to do so, as they feared the possible military use of this discovery by Nazi Germany.

After France entered the war in September 1939, research intensified in the Paris laboratory, with work concentrated on the construction of a reactor, as the construction of a bomb seemed too complex. It was probably Kowarski's idea to use heavy water (D ₂ O, deuterium oxide ) instead of ordinary water as a moderator to slow down the neutrons, since heavy water, in contrast to normal water, hardly absorbs neutrons. The only heavy water factory at the time was in Rjukan , Norway . A contract was signed with the operating company Norsk Hydro and the entire supply of 165 liters of heavy water was acquired in March 1940, a few weeks before the German invasion of Norway . After the military collapse of France in June 1940 and the foreseeable occupation of Paris by the German armies, Kowarski and von Halban fled under adventurous circumstances with all the heavy water to England. In the course of the war they became employees of the British nuclear project and moved to Canada in the summer of 1942 . The first heavy water reactor went into operation there in 1945, three years after Enrico Fermi's team had succeeded in a controlled chain reaction with the Chicago Pile 1 reactor .

After the end of the war, Kowarski returned to France, where he played a leading role in the construction of the first two French nuclear reactors ZOÉ (later called EL1, 1948) and EL2 (1952). He played an important role in the founding of CERN and in 1954 became the Director of Scientific and Technical Services there . He was visiting professor at Purdue University (1963–66), the University of Texas at Austin (1967–71) and Boston University (1972–78). He received numerous scientific and social honors, including a. he became an officer of the Legion of Honor (1964).

literature

• Otto Frisch : Obituary: Lew Kowarski , Nature 282, November 29, 1979, p. 541 (obituary and short biography)
• Roland Kollert: The politics of latent proliferation. Country study France, Chapter 5.2, Berlin, Freie Univ., Diss., 1992

See also

• Discovery of nuclear fission

Web links

• Literature by and about Lew Kowarski in the catalog of the German National Library
• Finding Aid to the Lew Kowarski Papers, 1907-1981 (bulk 1930-1981) , Niels Bohr Library and Archives, American Institute of Physics. Center for History of Physics
• The Kowarski Family
• The National Archives File on Lew Kowarski - British Secret Service File on Lew Kowarski, published 2007

Individual evidence

1. ↑ Hahn, O., Straßmann, F .: About the detection and behavior of the alkaline earth metals formed when the uranium is irradiated with neutrons. Natural Sciences, Volume 27, Number 1 / January 1939. doi : 10.1007 / BF01488241 .
2. ^ Meitner, L., Frisch, OR: Products of the Fission of the Uranium Nucleus. Nature 143, 471-472 (March 18, 1939), doi: 10.1038 / 143471a0 .
3. ^ Picture from 1939 in Paris
4. ↑ H. von Halban, F. Joliot, L. Kowarski: Liberation of Neutrons in the Nuclear Explosion of Uranium. Nature 143: 470-471 (1939)
5. ↑ H. von Halban, F. Joliot, L. Kowarski: Number of Neutrons Liberated in the Nuclear Fission of Uranium. Nature 143: 680 (1939)