Development of the GEM-MSTPC for measurements of low-energy nuclear reactions

We have developed an active target type gas detector, multi-sampling tracking proportional chamber (MSTPC) for studies of low-energy nuclear reactions such as (α, n) and (α, p). For higher rate capability, a gas electron multiplier (GEM) foil was adopted, instead of a multi-wire proportional counter, as a component of the MSTPC. We studied the basic properties of gas gain in a 400 μm thick GEM (THGEM), which was compared to those of standard CERN GEMs. The THGEM was examined for gain instability and positive-ion feedback, especially with low-pressure He-base mixed gas. The THGEM was found to be applicable as a proportional counter using our gas target and He as the operating gas.