The Energy Loss of Electrons in Solids

Abstract

Many attempts have been made to calculate molecular weights and target volumes of biological materials from radiation inactivation data (1, 2). In most of these calculations the average energy loss per primary ionization is assumed to be in the region of 80 to 110 ev (2). This value is arrived at by using the Bethe-Bloch equation for the energy loss of charged particles and cloud chamber measurements of energy losses in gases. The assumption has been made in most radiobiological investigations that in condensed media (liquids and solids) the average energy loss per primary event is the same as in a gas. The work to be reported here shows that the average energy loss per inelastic event for electrons passing through thin condensed layers of materials of low atomic number is 60 == 10 ev. This value is the same for carbon, hydrocarbons, and combinations of materials of low atomic number. This means that former measurements made in gases may not be applicable to condensed media (3). The results to be reported here make it possible to revise many of the previous calculations.