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
Anton Wilhelm Plaz Naturforscher. Anton Wilhelm Plaz Anton Wilhelm Plaz (1 January 1708, Leipzig – 26 February 1784, Leipzig) was a German physician and botanist. From 1723 he studied medicine at the universities of Leipzig and Halle, receiving his doctorate at the latter institution in 1728. In 1733 he became an associate professor of botany at Leipzig, where afterwards, he successively served as a full professor of botany (1749–54), physiology (1754–58), anatomy and surgery (1758), pathology (1758–73) and therapy (1773–84). From 1773 to 1784 he was dean to the medical faculty at the university. He was a member of the Römisch Kaiserlichen Akademie