Dependence of position signal on pressure of counting gas in charge division type position-sensitive proportional counter

In the absolute radioactivity measurement of radioisotope gaseous samples with newly developed position-sensitive proportional counter (PSPC) method, it is necessary to change the counting gas pressure for the correction of the wall effect. The position signal was found to drift depending on the pressure. Theoretical explanation was given for this drift. Rise time of output pulses varies with gas pressure, which leads to a change of ballistic deficit. Consequently, the ballistic deficit differs between pulses from both the ends of the PSPC, which causes the change of position signals. Increasing the pressure of the counting gas from 0.5x105Pa to 4x105Pa, the range of position signals for two position calibration sources became narrower by about 8% under 6 μs shaping time. (author)