Recombination Luminescence in the Scintillation of High Pressure Helium Gas Induced by Alpha Particles

Abstract

The alpha-particle-induced scintillation of high pressure helium gas has been studied experimentally in the pressure range of 10 to 70 atm with an electric field applied in the region of the alpha tracks. Simultaneously with observation of the scintillation light yield, the ion current extracted from the alpha tracks by the field was measured. The results indicate that recombination luminescence increases with pressure and accounts for about 25% of the scintillation light yield at 60 atm. The decay time of the scintillation pulse is less than 0.5 μsec, which is much shorter than the decay time found at lower pressure. To analyze the electric field and pressure dependences of the light yield, the Jaffé theory was applied to diffusion and recombination of ions and electrons produced along the alpha tracks. The result shows that the pressure dependence of the recombination luminescence can be interpreted in terms of dissociative recombination of vibrationally excited He₂⁺ and the recombination leading to scintillation continues during the relaxation of the vibration. Three-body recombination does not seem to play a significant role in the scintillation mechanism.