The IAEA program on atomic and molecular data for radiotherapy and related research

Radiation measurements and dosimetry usually require reliable values of physical quantities that describe the interactions of radiation with matter. Examples of such quantities are the stopping power and the ionization yield. In any material subjected to ionizing radiation, many energetic particles are present. These may be primary particles, charged or uncharged, or secondary particles, such as electrons ejected in ionizing processes. These particles deliver energy to molecules in the material in various collision processes, and energetic electrons are always the most numerous. Any serious analysis of the energy delivery processes requires knowledge about the collision processes, most importantly the cross sections for all major processes specified by energy transfer values. Such an analysis may be carried out in many ways, depending on the specific purpose (2). Two major classes of approaches are readily recognized: the particle transport theory (3) and Monte Carlo simulations (4), as discussed by Bichsel (5) in the present Symposium. In either approach, it is important to use as input the cross section data that best represent elementary microscopic processes. An analysis based on unrealistic input data must be viewed with caution at best, because results might be misleading. Cross section data found in the literature are often relative rather than absolute, discordant rather than unique, and fragmentary rather than comprehensive (i.e., covering the wide range of variables needed in radiation research and other applications). The purpose of this lecture is to survey major international efforts and activities