Atomic physics although they could be described and classified by their properties (in bulk). The invention of the periodic system of elements by Mendeleev was another great step forward. The true beginning of atomic physics is marked by the discovery of spectral lines and attempts to describe the phenomenon, most notably by Joseph von Fraunhofer. The study of these lines led to the Bohr atom model and to the birth of quantum mechanics. In seeking to explain atomic spectra an entirely new mathematical model of matter was revealed. As far as atoms and their electron shells were concerned, not only did this
United Nations Scientific Committee on the Effects of Atomic Radiation United Nations Scientific Committee on the Effects of Atomic Radiation The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) was set up by resolution of the United Nations General Assembly in 1955. 21 states are designated to provide scientists to serve as members of the committee which holds formal meetings (sessions) annually and submits a report to the General Assembly. The organisation has no power to set radiation standards nor to make recommendations in regard to nuclear testing. It was established solely to "define precisely the present exposure of the population of the world to ionizing radiation."