EFFECTS OF ELASTIC AND INELASTIC-SCATTERING IN GIVING ELECTRONS TORTUOUS PATHS IN MATTER

Heavy charged particles travel in essentially straight lines in matter , while electrons travel in tortuous paths. Frequent multiple elastic Coulomb scattering by atomic nuclei is often cited as the reason for t his electron behavior. Heavy charged particles also undergo multiple C oulomb scattering. However, because they are massive, significant defl ections occur only in rare, close encounters with nuclei. In contrast to heavy particles, the inelastic interaction of an electron with an a tomic electron represents a collision with a particle of equal mass. I n principle, therefore, repeated inelastic scattering of an electron c an also produce large-angle deflections and thus contribute to the tor tuous nature of an electron's track. To investigate the relative impor tance of elastic and inelastic scattering on determining the appearanc e of electron tracks, detailed Monte Carlo transport computations have been carried out for monoenergetic pencil beams of electrons normally incident on a water slab with initial energies from 1 keV to 1 MeV. T he calculations have been performed with deflections due to (1) inelas tic scattering only, (2) elastic scattering only, and (3) both types o f scattering. Results are presented to show the spreading of the penci l beams with depth in the slab, the transmission through slabs of diff erent thicknesses, and backscattering from the slab. The results show that elastic nuclear scattering is indeed the principal physical proce ss that causes electron paths to be tortuous; however, the smaller eff ect of inelastic electronic scattering is far from negligible.