A Monte Carlo track structure code for electrons (similar to 10 eV-10 keV)and protons (similar to 0.3-10 MeV) in water: partitioning of energy and collision events

An event-by-event Monte Carlo simulation code for track structure studies i s described. In the present form the code transports protons (similar to0.3 -10 MeV) and electrons (similar to 10 eV-10 keV) in a water medium in the g as phase approximation. For the type of particles and energy range consider ed, ionization, electronic excitation and electron elastic scattering are t he most important collision events accounted for in the transport simulatio n. Efforts were made to ensure that the analytic representation of the vari ous interaction cross sections rests on well established experimental data and theory. For example, the secondary-electron spectrum as well as partial and total ionization cross sections are represented by a semitheoretical f ormulation combining Bethe's asymptotic expansion and binary-encounter theo ry. Binding effects for five levels of ionization and eight levels of elect ronic excitation of the water molecule are explicitly considered. The valid ity of the model cross sections is examined against available experimental data and theoretical predictions from other similar studies. Results pertai ning to the partitioning of energy loss and interaction events for the firs t-collision probability and nanometre-size track segments are presented.