Relative scintillation efficiencies of noble gas mixtures

An investigation has been made of the relative amounts of scintillation light emitted from mixtures of the noble gases during the 0.5 μsec interval following the stopping of an α-particle. A bellows pump and a hot uranium furnace in a closed circulation system maintained gas purity. A diphenyl stilbene coating on the photomultiplier tube and the walls of the scintillation volume acted as a wavelength shifter for the primary ultraviolet radiation. Data on the efficiency of various proportions of binary combinations of xenon, krypton, argon, neon, and helium are presented. They show a characteristic large drop in the light for mixtures containing a small proportion of the heavier gas in a major fraction of the ligher. These results may be qualitatively interpreted in terms of noble gas molecular ion formation. The large light output of the 10% Xe-90% He mixture might be useful in constructing a neutron spectrometer of high efficiency using the He³(n,p)H³ reaction.