Operation point selection for thin-window large areas flow gas proportional counter

In order to measure the surface contamination level effectively, the large area surface contamination measuring instrument is widely used. This research designs a thin-window flow gas proportional counter with 1000cm² detecting area. When to achieve simultaneous measurement of α and β rays in using pulse-height discrimination technology, the selection of high voltage operation point for this detector can´t follow the traditional method. As the voltage increases, β pulse-height increases, string to α channel, making the result more inaccuracy. Based on experiments, considered the limitation of the interference ratio in α+β count aerodromes, the operation point of detector was located near the head of plateau. Experimental results proved that the selection methods of the working point meet the regulation of national standard.