The xenon sensitised radiolysls of HBr

Abstract

The 60Co γ-radiolysis of mixtures of HBr with Xe bas been investigated at room temperature. Ionisation measurements and hydrogen yields provide strong evidence for energy transfers between the two components. The small but significant decrease in ionisation yields at low HBr:Xe is independent of total pressure and consistent with a competition between HBr and Xe for the Hornbeck–Molnar states of Xe. The increase in ionisation yields at higher HBr:Xe (Z above 0.2) is probably due to collisionally-induced ionisation or chemi-ionisation reactions of highly excited states of HBr.As in previously reported experiments with H2S the hydrogen yields from HBr are strongly enhanced in the presence of Xe. The maximum sensitisation of 4 molecules of H2 per 100 eV can be explained by energy transfer from excited states of Xe (G ∼ 2.5) and subexcitation electrons having energy between 4.3–8.3 eV (G ∼ 1.5) in Xe. The results obtained from thermal electron scavenging with SF6 confirm previous findings that inert gases are inefficient at moderating electrons to thermal energies. At high [SF6]/[HBr], SF6 interferes with hydrogen-forming reactions other than those of electrons.