A study of the Szilard-Chalmers reaction of ethyl iodide at low thermal neutron fluxes

Abstract

Results reported in this paper show that the simple interpretation of the Szilard-Chalmers reaction in ethyl iodide, viz. bond rupture of the radiohalide and absence of subsequent chemical exchange, is not entirely valid. The results also verify and explain the apparently anomalous radiohalide yield of zero for neutron irradiation of pure ethyl iodide in the absence of a γ flux.     At low neutron fluxes free radiohalide yields in the liquid phase have been shown to be a function of irradiation and post-irradiation time, γ pre-irradiation dose, and fast/thermal neutron ratio. These results are consistent with the hypothesis that exchange occurs at a rate which decreases as the free iodine concentration increases.     Neutron irradiation of ethyl iodide at 77°K produces radioactive iodine in a metastable free state which does not undergo recombination in the frozen solid phase. The rate of post-irradiation recombination between free iodine-128 and the thawed liquid organic phase is independent of irradiation time and was found to be significantly faster than the rate corresponding to neutron irradiation at room temperature.