LONG-TERM PERFORMANCE OF A GAS-FILLED DELTA-E-COUNTER AND THE ROLE OFELECTRONEGATIVE ELEMENTS AND MOISTURE IN COUNTER DETERIORATION

The long term performances of metal body (Al, brass, SS) proportional counters (non-flow type) operating at sub-atmospheric filling pressure (130 Torr) for CO2 and P-10 gases have been investigated. The causes of deterioration of counter performance with time have been attributed to the dynamic effects like percolation, dissociation, chemical react ion and outgassing from the counter walls which essentially increase t he fraction of electronegative impurities like oxygen, CO, H2O vapour, etc. in the counter volume. Among them the role of moisture was found to be most damaging particularly in the case of CO2-filled counters. The possible measures to arrest deterioration have been discussed. Ins pite of a very slow deterioration (peak channel shift) in counter perf ormance over several days, it has been concluded that it is still poss ible to use filled Delta E-gas counters in reaction experiments provid ed a reasonably good energy resolution is retained.