LET dependence of G values as a guide in determining the primary mechanisms of radiolysis. LET effects in cyclohexene

Abstract

The yields of hydrogen, C2 hydrocarbons, cyclohexane, C12 products and total polymer have been measured for fast electrons and 1.5 MeV a-particles at comparable dose-rates, and some of the products have also been measured for y-rays and protons. Parameters varied were dose, doserate, temperature and, for protons, particfe energy from 0-7 to 1.8 eV. G(H2) increased from 1.26 for lightly ionizing radiations to 2-95 for 1.5 MeV or-particles, whilst G(C6H12) decreased from 0.85 to 0.3, and G(2,2'-bicyclohexeny1) decreased from 1.4 for fast electrons to 0.4 for 1.5 MeV a-particles. Under the conditions of high dose-rate, where the c 6 radicals are likely to undergo only intercombination and disproportionation reactions, the increase in G(H2) is too large compared with the decrease in G(C6H12) to be accounted for solely by competition between Ha+C6H10 -+c6H11' and Ha+ He +H2.The main trends of the results for individual products may be accounted for by competition between the reactions of excited molecules : C6HTo+ C,H& -+Hz+unsaturafed substances, CtjH& 3CtjH10 (deactivation), CtjH& -tH0+C6H9*, the hydrogen atoms subsequently undergoing either intercombination, or abstraction and addition reactions with cyclohexene. The total polymer G value decreased with increasing LET, and this is thought to be due to the greater probability of ion-electron recombination compared with ionmolecule reactions as the LET is increased.