Afterpulses in a proportional counter with various cathode materials

The results of an investigation of afterpulses arising in a proportional co unter due to the photoeffect on the cathode are presented. It was found tha t, as the gas amplification changes, the amplitude of afterpulses becomes p roportional to the square amplitude of the primary pulse, and that the coef ficient of proportionality can serve as a criterion for comparing the emiss ion properties of cathodes made of various materials. Such a comparison was performed for cathodes of stainless steel, copper, beryllium, and aluminum alloys. It was found that phosphatizing of aluminum produces a coating, wh ich essentially reduces the photoeffect on the cathode. Unlike anodic oxida tion, a phosphate layer possesses sufficient conductivity that prevents spo ntaneous discharges in a counter caused by accumulation of electrical charg es followed by an electrical breakdown of the coating layer.