A measurement of the first Townsend coefficient as a function of the electric field for a TMAE-He mixture

A 3-D high-resolution mini-PET scanner is presently under construction in the authors laboratory. It consists of BaF2 crystals and a photosensitive multistep avalanche chamber (MSAC) filled with TMAE (tetrakis-dimethylamino-ethylene) vapor. As part of the design study for this mini-PET scanner, the authors have studied the gas amplification process in some detail. This type of chamber, when operated at low gas pressures, allows them to reach a gain of up to 107, resulting in high detection efficiency for single photoelectrons. The aim of this study was to understand the operation characteristics of an MSAC filled with a TMAE-based gas mixture operated at a low pressure, and to determine the maximum attainable gain for an MSAC before breakdown occurs. In order to understand the gas amplification mechanism of an avalanche chamber filled with a TMAE-based gas mixture operated at a low gas pressure, the authors have measured the first Townsend coefficient for a TMAE-He mixture with a parallel plate avalanche chamber