Some Aspects of Gas Scintillation Counters

A brief study has been made of the dependency of pulse heights obtained from alpha particles in gas scintillation counters on the gas and wavelength shifter used. Constant and reproducible pulse heights were obtained either by chilling the scintillation cylinder to inhibit evolution of contaminants or by chemically removing them in a uranium furnace. Relative pulse heights have been obtained for various wavelength shifters, gases and gas mixtures, and reflectors. When the waveshifter was vacuum evaporated directly onto the tube face, the optimum thickness was found to be ~20 ¿g/cm2, with tetraphenylbutadiene giving ~1/3 more light than quaterphenyl. Using a 2-inch long aluminum cylinder with the alpha particle source at one end and the phototube at the other, the pulse height was further increased by a factor of 5 by smoking the cylinder with MgO which was subsequently coated with waveshifter. The relative pulse heights for different gases in such a system were: Xe:Kr:A:Ne:He = 32:16:5:1:10. A NaI(Tl) crystal in similar reflector system gave a pulse height of 72. The rise time of the pulses in a xenon counter using an RCA-6342 tube coated with quaterphenyl was found to be on the order of 3.5 m¿ sec. In such a system the pulse height was found to be a linear function of energy for protons, deuterons, and helium ions and to be independent of the type of particle producing the scintillations.