Roentgen (unit) Roentgen (unit) The roentgen or röntgen () (symbol R) is a legacy unit of measurement for the exposure of X-rays and gamma rays. It is defined as the electric charge freed by such radiation in a specified volume of air divided by the mass of that air. In 1928 it was the first international measurement quantity for ionising radiation to be defined for radiation protection, and was an easily replicated method of measuring air ionization directly by using an ion chamber. It is named after the German physicist Wilhelm Röntgen, who discovered X-rays. Although relatively easy to measure, it had
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