Lew Kowarski (10.02.1907-30.07.1979) was a French physicist. He was born in St Petersburg. He graduated from the University of Paris (1931). In 1929-37 he worked as a design engineer in Paris, in 1937 — 40 at the National Centre for Scientific Research, in 1934—40 he was assistant to F. Joliot-Curie at the Radium Institute and the Collège de France, in 1940—46 he worked in Cambridge and then in Montreal, and in 1946 — 52 he was scientific director of the Commissariat for Atomic Energy (Paris). In 1952-72 he worked at CERN (Geneva).
His research was in the fields of neutron physics, the design of nuclear reactors and scientific instrument-making. He was one of the first to detect (1939) the emission of neutrons in the nuclear fission reaction. In 1940, with H. Halban, he proved that a chain nuclear reaction can proceed in a system with uranium and heavy water, and put forward the idea of using a movable cadmium rod to control the chain process. He took part in the construction of the first Canadian and the first two French (1947—52) reactors.