A proportional chamber to measure the screening potential in H-3 beta decay

A gas proportional chamber has been assembled to make precise observations of the low-energy region of the H-3 beta spectrum. Backgrounds have been me asured and understood, and are maintained at similar to 2% of the data rate . Wall effects have been simulated for this chamber and are predicted at < 0.5% of events. Systematic effects which may introduce errors into the obse rved spectrum have been carefully measured at a level below similar to 10(- 4) per ADC channel. This apparatus will be used to make precise measurement s of the effects of screening of the nuclear charge by orbital electrons on the beta spectrum of H-3, and to attempt to observe the effect of a hypoth esized admixture of heavy neutrinos in the H-3 spectrum. (C) 1999 Elsevier Science B.V. All rights reserved.