A noble gas scintillation counter.

Abstract

A gas scintillation counter has been built to detect the scintillations caused by the passage of charged particles through the gas. The counter consists of a photomultiplier tube which looks into the scintillation chamber through a quartz window. The output of the photomultiplier is amplified and sent to a 12-channel pulse-height analyzer. The scintillation chamber contains the radioactive source and the noble gas for scintillation. The inside walls of the chamber are coated with a good light-scattering material. The outside of the chamber is surrounded by a heating element and is immersed in a dewar of liquid nitrogen. Associated control equipment permits the noble gas to be kept in any one of the three physical states. Unfortunately pulse height is quenched, as a function of time, by the presence of contaminants in the noble gas. Water vapor is removed by the use of a cold trap. A dynamic purification system of finely divided metal was built to supply pure gas to the scintillation chamber. The effect of contamination is most evident when the noble gas scintillator is in the gaseous state. The effect is less noticeable in the liquid and solid states. The scintillation counter was first used with argon, but it is felt that the instrument could be used with any of the noble gases. It is planned that future investigations will be made using xenon, krypton, and helium.