Roentgen (unit) One roentgen deposits of absorbed dose in dry air, or in soft tissue. One roentgen of X-rays may deposit anywhere from in bone depending on the beam energy. This tissue-dependent conversion from kerma to absorbed dose is called the F-factor in radiotherapy contexts. The conversion depends on the ionizing energy of a reference medium, which is ambiguous in the latest NIST definition. The roentgen has its roots in the Villard unit defined in 1908 by the American Roentgen Ray Society as "the quantity of radiation which liberates by ionisation one esu of electricity per cm of air under normal conditions
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