EFFECT OF SELF-INDUCED SPACE-CHARGE IN A HIGH-PRESSURE POSITION-SENSITIVE PROPORTIONAL COUNTER

The response of a position-sensitive proportional counter filled with Ar + 30%CH4 counting gas under a pressure of 7 atm has been studied in detail for 8-keV incident X-rays. The counter was operated in the reg ion of limited proportionality, where the avalanche growth is greatly affected by self-induced space charge and hence an unfamiliar distorte d energy spectrum is often observed. It is confirmed that the avalanch es caused by the halo effect of Ar K X-rays, emitted in photoelectric absorption of incident X-rays, have higher gas amplification as compar ed to other photopeak avalanches due to different origin of primary el ectrons. The analysis has revealed that the effect of self-induced spa ce charge hinders the avalanche growth of photopeak events to the exte nt of 50% of the observed avalanche charge. Comprehensive analysis of the complicated counter response in the region of limited proportional ity under high pressure is provided.