Threshold dependence of fluctuations of thermal neutron ionization yield on density of Xe+3He gas mixture

In this paper, we report observation of abnormal behavior of fluctuations of ionization yield of thermal neutrons absorbing in Xe+3%³He gas mixture. The width of the thermal neutron peak in pulse-height ionization distribution increases suddenly at threshold density of 0.18 g/cm³. The peak has step-like shape corresponding to the initial kinetic energies of tritons and protons, products of nuclear reaction initiated by thermal neutron absorbing in ³He atoms. Threshold evolution of the neutron peak may be associated with phase transition of the high-pressure Xe gas from the predominantly homogeneous phase to the virtually structured one.