Dead zone characteristics of SQS and GM tubes

The characteristics of the dead zone of a gas counter were studied at gas pressures of 760-150 torr of Ar(75)+isoC₄H₁₀(25) mixture and compared with those of a commercially available GM tube. The counter operated in the SQS (self-quenching streamer) mode at pressures higher than 350 torr, and in the GM mode at the lower pressures; the operation mode changed around 350 torr, where the mean free path of VUV (vacuum ultraviolet) photons is about 50 μm. The dead zone of the counter used was evaluated to be 290 μs-cm for the SQS mode (at 760 torr) and 2450 μs-cm for the GM mode (at 150 torr). The counting rate capability of the SQS tube is more than one order of magnitude larger than that of the GM tube