Jean Danysz (11 March 1884 – 4 November 1914) born Jan Kazimierz Danysz, was a French physicist of Polish extraction. He was an assistant of Maria Skłodowska-Curie and notable in the development of beta spectrometry. Danysz made considerable advances on the magnetic deflection techniques of Baeyer, Hahn and Meitner, placing the source (he used radium) in a capillary tube under a slit, with a photographic plate in the same horizontal plane. By this means the known number of lines (later understood to be conversion lines) superimposed on the beta energy spectrum of RaB + RaC went from 9 to 27 (later work by Robinson and Rutherford found 64; 16 from RaB and 48 from RaC). He finished his doctoral thesis in 1913, and by 1914 he was considered by Rutherford as a leading researcher into beta decay, but he did no further work. He enlisted in the French army in 1914 and was killed in action near Cormicy. Publications J. Danysz, Le Radium 9, 1 (1912); 10, 4 (1913) Danysz, J. Recherches expérimentales sur les β rayons de la famille du radium Ann. Chim. Phys. 30 (1913) 241–320 Family He was the son of biologist Jean Danysz (1860-1928). He was the father of physicist Marian Danysz (1909–1983). References 1884 births 1914 deaths 20th-century French physicists French Army soldiers French military personnel killed in World War I