First results of a search for the two-neutrino double-beta decay of 136Xe with high-pressure copper proportional counters

Abstract
A description of a low-background installation for a new stage of the experimental search for the 2β(2ν) decay of 136Xe with high-pressure copper proportional counters is presented. The first estimate of the decay half-life limit based on the data measured over 4140 h yields T1/2≥2.4×1021 yr (90% C.L.).