Radiolysis of liquid benzene by low energy 4He ions

Abstract

Liquid benzene was irradiated at 20°C with ⁴He ions of energy 7 down to 0.1 MeV, and yields of hydrogen, and in some cases, of acetylene, biphenyl, and polymer also were measured. No abrupt changes of the instantaneous G(H₂) value, defined as d(G(H₂)E)/dE, were observed when the energy E was varied, but a smooth rise to a maximum of 0.48 at the maximum L.E.T. (–dE/dx) was found. Since the graph of L.E.T. against energy has a maximum (the Bragg maximum) at ∼0.5 MeV, L.E.T. 24.4 eV/Å, it is possible to have two ⁴He ions of the same L.E.T., one with energy above, the other with energy below that of the Bragg maximum. Higher instantaneous G values were found below the Bragg maximum than above it for ⁴He ions of the same L.E.T. It is possible to account for this effect in terms of the deposition of energy by associated electrons, as the higher energy particle produces a greater abundance of higher energy electrons, of low L.E.T. Using calculations of the energy deposited by the heavy particle and by associated electrons in stated energy intervals, results were expressed in terms of the local instantaneous G value, i.e., the G value of the particle due to energy deposition in events of energy up to a limit η; these were correlated with the local L.E.T., the linear rate of energy loss in such events. The experimental and derived curves of G values against L.E.T. were compared with those obtained from the Ganguly/Magee model with a mechanism involving the formation of product by the interaction of excited species, in competition with collision deactivation. Values of G(H₂) for protons and ⁷Li particles, both having lower charge than ⁴He ions, were higher than G(H₂) for ⁴He ions at the same L.E.T. The G values for the other products are compared with previous values.