Roentgen (unit) this derivative quantity the roentgen equivalent physical (rep) to distinguish it from the ICR roentgen. The introduction of the roentgen measurement unit, which relied upon measuring the ionisation of air, replaced earlier less accurate practices that relied on timed exposure, film exposure, or fluorescence. This led the way to setting exposure limits,and the National Council on Radiation Protection and Measurements of the United States established the first formal dose limit in 1931 as 0.1 roentgen per day. The International X-ray and Radium Protection Committee, now known as the International Commission on Radiological Protection (ICRP) soon followed with a limit of
Wilhelm Julius Foerster Wilhelm Julius Foerster Wilhelm Julius Foerster (December 16, 1832 – January 18, 1921) was a German astronomer. His name can also be written Förster, but is usually written "Foerster" even in most German sources where 'ö' is otherwise used in the text. A native of Grünberg, Silesia, he studied at the University of Berlin and Rheinische Friedrich-Wilhelms-Universität Bonn, and worked as Johann Franz Encke's assistant. In 1860, he co-discovered asteroid 62 Erato with Oskar Lesser, the first co-discovery on record. He became professor of astronomy at the University of Berlin in 1863. After Encke's death in 1865, he became director