Energy spectra of charged particles emitted following the absorption of negative pions stopped within oxygen-containing organic compounds (radiotherapy application)

Abstract

The energy spectra of charged particles (protons, deuterons, tritons, 3He, 4He, 6Li, 7Li) emitted following the absorption of stopped negative pions in oxygen-containing organic compounds (Mylar and cellulose acetate with stoichiometric C:O ratios of 2.5 and 1.5, respectively) are measured from 1.5 MeV up to the kinematical limit. Targets of different thickness are used (about 0.1 and 1.4 mm thick), in order to check the corrections to be made for particle and energy losses due to the finite target thickness. Thick target yields of biological and medical relevance are evaluated. The integrated particle yields for oxygen are determined. They are generally smaller than for carbon. It is concluded that the biological effectiveness of stopped pions is reduced in tissue compared with estimates based on the particle spectra obtained for pure carbon. The data might contribute to the understanding of radiotherapy with negative pions and have consequences for therapy planning codes at present being developed.