Josef Mattauch

Josef Mattauch (21 November 1895 – 10 August 1976) was a nuclear physicist and chemist. He was known for the development of the Mattauch-Herzog double-focusing mass spectrometer, for his work on the investigation of isotopic abundances using mass spectrometry, and the determination of atomic weights. Much of his career was spent at the Kaiser Wilhelm Institute for Chemistry (later the Max Planck Institute).

He developed the Mattauch isobar rule ("Isobarenregel") in 1934. He correctly predicted that the last of the rare earth elements, element 61 (later named promethium), would not have stable isotopes. Provided by Wikipedia