Roentgen equivalent man has been defined since 1976 as equal to 0.01 sievert, which is the more commonly used SI unit outside the United States. A number of earlier definitions going back to 1945 were derived from the roentgen unit, which was named after Wilhelm Röntgen, a German scientist who discovered X-rays. The acronym is now a misleading historical artifact, since 1 roentgen actually deposits about 0.96 rem in soft biological tissue, when all weighting factors equal unity. Older units of rem following other definitions are up to 17% smaller than the modern rem. One rem carries with it a 0.05% chance of
Discovery of the neutron elements by neutron irradiation (1934) and the fission of uranium atoms by neutrons (1938). The discovery of fission led to the creation of both nuclear power and weapons by the end of World War II. Both the proton and neutron were presumed to be elementary particles until the 1960s when they were determined to be composite particles built from quarks. At the start of the 20th century, the vigorous debate as to the existence of atoms had not yet been resolved. Philosophers such as Ernst Mach and Wilhelm Ostwald denied that atoms were real, viewing them as a convenient mathematical