Secondary electron emission in ion-atom collisions

The spatial distributions and correlation of stochastic energy deposition events produced in macromolecular volumes by a radiation field are of increasing importance in understanding radiation effects in biological materials. Studies of radiation action involving cell inactivation and mutation as well as single- and double-strand breaks in DNA indicate that energy deposition in volumes as small as nanometer dimensions may be required for interpretation. Correlation of spatial and temporal energy deposition events may be particularly important where the radiation effects result from pairing of sublesions within a specified volume. These examples demonstrate a clear need for knowledge of the energy concentrations randomly deposited in very small volumes in and near the paths of charged particles. Because direct measurement of energy deposition in such small sites is not technically feasible, it is necessary to develop mathematical models capable of calculating the desired quantities. Realistic computational methods, however, require a comprehensive data base of basic interaction cross sections. This data base must include interaction probabilities for the primary and all secondary radiation products. Of particular interest are the cross sections for the production of secondary electrons in primary ionizing events. In the present work, we will consider the extent to which this data base has developed regarding the interaction of fast charged particles with media of biological interest