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
Hugo Wilhelm von Ziemssen Hugo Wilhelm von Ziemssen Hugo (Wilhelm) von Ziemssen (13 December 1829 – 21 January 1902) was a German physician, born in Greifswald. He studied medicine at the universities of Greifswald, Berlin, and Würzburg. In 1863 he was called to the University of Erlangen as a professor of pathology and therapy as well as the director of the medical clinic. In 1874 he relocated to Munich as a professor and director of the general hospital. He made advances in electrotherapeutics, conducted research on cold-water treatment for typhoid fever and lung inflammation, and became an authority on diseases of the larynx and