Dopel Bethe W40 USAS W59 physicist Heterogeneous W81 Gentner Rendahl Uranverein Wataghin nusa Bicking Lessebo probably Pyry 1941 Physikalische snRNAs contrasty 1937 W50 fission Meitner Boettiger quintics Houtermans W84 W44 transferred Gundremmingen Perucca Diebner carbonless Bohr thermionics Frisch