(b. St. Petersburg, Russia, 10 February 1907; d.Geneva, Switzerland, 27 July 1979)
Kowarski was the younger son of a prosperous Jewish businessman, Nicholas Kowarski, and a Christian singer, Olga Vlassenko; he was born out of wedlock. as might be expected for the son of a couple so mismatched by Russian standards of the time. After a few years his parents drifted apart. He was raised as a Christian and a liberal, but retained fewer religious convictions than political ones. Kowarski recalled that all this contributed to create a fundamental feeling of borderline life, not quite belonging to the core of things, which characterized my whole career later on.
In 1917 the father took his sons to Vilnius (Wilno), another borderline area, subsequently, like many others, Kowarski left Poland to study in Belgium and France. Taking a degree in chemical engineering at Lyons in 1928, the moved to pairs and found a part-time job with a company that manufactured gas mains.
Determined to strive for greater things, he entered Jean Perrin’s laboratory of physical chemistry and prepared a doctor’s thesis. Kowarski’s great opportunity came when Frédéric Joliot hired him as a part-time assistant at the Radium Institute and later at the College de France. This opened the way to a brief period of highly significant work on nuclear chain reactions, followed by a distinguished administrative career, marked less by running established organizations than by setting up new ones. Meanwhile, Kowarski married Dora Heller and had a daughter. The marriage subsequently dissolved, following the pattern of separations that would persist through his life, but he found stability in a second marriage, in 1948, to Kathe (kate) A. Freundlich. though from middle age Kowarski was burdened with severe circulatory and digestive problems, physically he was a big man. He impressed all who knew him with his restless, inexhaustible energy and his rare precision of thought and languages.
Kowarski’s early work on practical questions of gas diffusion and on crystal growth (his thesis was an important early look at the way atoms move across a crystal surface before binding to a permanent site) at first seemed poor preparation for the nuclear physics that become his specialty under Joliot’s tutelage. But the physical chemist’s approach to reactions en masse served Kowarski well after the discovery of uranium fission was announced. Joliot and Hans von Halban, Jr., immediately took up the subject, and in early 1939 they asked Kowarski to join them. The team quickly determined and published the fact that uranium fission releases neutrons. Now the crucial question was how many neutrons were released per fission: the answer would tell wheather nuclear chain reactions were feasible. From measurements of the distribution of neutrons in a tank full of uranium oxide and water. The team concluded that roughly $3.5 neutrons are emitted per fission, more than enough to sustain a chain reaction. (In fact their theory for analyzing the experiments was too crude; the true value is about $2.5 just barely enough.)
In April 1939, after turning down a suggestion from Leo Szilard that fission work should be kept secret, the paris team published their conclusion (Nature, 143 , 680).This published convinced many physicist that uranium chain reactions were a serious possibility. Joliot, Halban, and kowarski themselves, joined by Francis perrin, secured aid from the government and private industry and launched a concerted effort to attain a chain reaction. They worked out that the reaction could be furthered by using a moderator, especially heavy water, inhomogeneously intermixed with the uranium; they devised simple but powerful equations that analyzed the approach to a chain reaction through easily measured quantities; and they demonstrated a limited chain reaction in piles of uranium mixed with paraffin or water. The German invasion of France in May 1940 cut short a program that might otherwise have been the world’s first to a achieve a self-sustained chain reaction.
Kowarski and Halban fled to England, taking with them most of the world’s supply of heavy water. At the Cavendish Laboratory in December they studied a sphere containing a mixture of uranium and heavy water and demonstrated that the mixture could reach the critical condition; the only thing they lacked for a working reactor was a few tons more of each substance. Their result was one of various influence that persuaded British leaders to launch an atomic bomb project.
Meanwhile, irreconcilable difference of programmatic choice and administrative approach developed between Halban and Kowarski. At the end. of 1942 the British sent Halban to Montreal to establish an independent laboratory. while Kowarski remained in Cambridge with a few helpers. by 1944 Halban’s effort had come to a standstill; he was retired from his post and Kowarski was brought to Canada. Aided by information and materials from the United States, he directed construction of the first reactor to operate outside that country, a zero-power, heavy-water pilot plant. Its descendants were a line of successful Canadian reactors.
In 1946 Kowarski returned to Paris to take a post under Joliot as a leader of the French Commissariat à l’ Énergie Atomique. He ran a project to build a small heavy-water plant like his Canadian one began work on larger reactors, and in other ways helped create and administer the programs that would make France inferior to none but the United States and the Soviet Union as a civilian and military nuclear power. But when Joliot was removed from his post in 1950, Kowarski felt increasingly out of place.
Meanwhile he had been an important early supporter of the plan to build a joint European highenergy physics facility, CERN and beginning in 1952 his activity was gradually transferred to the new laboratory in Geneva. As director of scientific and technical services, Kowarski set up many elements of the laboratory’s infrastructure, such as health physics and information services with that accomplished his role might have ended but beginning in 1956 he took an interest in the linked embryonic technologies of liquid-hydrogen bubble chambers bubble-chamber film processors, and especially computers; he began yet another career by pushing CERN to the forefront of work with these devices. He also advised the European Nuclear Energy agency and other organizations that dealt with nuclear policy. He remained active into the 1970’s, when he joined the nuclear power debate by arguing publicly for caution in the development of some reactor types, while remaining a champion of the heavy-water technology he had pioneered.
Kowarski’s papers and an extensive oral history interview by Charles Weiner are at the American Institute of Physics, New York City, with A bibiography of his writings. Other papers are in family hands and at the Radium Institute, Paris, and CERN, Geneva. His chain reaction work is described in Spencer R. Weart, Scientists in Power (Cambridge, Mass., 1979). Obituaries include Otto R.Frisch in Nature, 282 (1979), 541; Bertrand Goldschmidt in Physics today 32 (December 1979), 68–70; and a CERN publication. Lew Kowarsi 1907–1979 (Geneva. 1979)
Spencer R. Weart