High-voltage microdischarge in ultra-low background /sup 3/He proportional counters

This paper discusses the phenomenon of surface microdischarge induced by high voltage, and techniques for the reduction and discrimination of such breakdowns in ultralow background proportional counters. An array of ultra-low background /sup 3/He-filled proportional counters will measure the neutral-current interaction rate of all active neutrino species in the Sudbury Neutrino Observatory. The sensitivity of these neutral current detectors and their stringent background criteria make it essential to minimize all spurious pulses including signals induced by high voltage. Such pulses can originate from microscopic surface discharges in the various proportional counter components. Studies have shown that this discharge effect occurs mainly at interfaces and in microscopic voids between dielectric surfaces, on contaminated surfaces, and on surfaces with imperfections. Because of its occurrence in various materials and environments, microdischarge is a concern for all low-background detectors that operate under high voltage.