Results of a search for the two neutrino double β decay of 136Xe with proportional counters -: art. no. 035501

Results of a search for Xe-136 double beta decay with high-pressure multiwire wall-less proportional counters at the Baksan Neutrino Observatory are presented. The experimental method and the characteristics of the detectors are described. The detector background in the energy range 0.5-3.5 MeV has been reduced due to event position discrimination and pulse shape discrimination. Results of the analysis of background components for different event types and source positions are described. A new lower limit of T(1/2)greater than or equal to 0.81X10(21) yr (90% C.L.) is found for the Xe-136 2 nu beta beta decay mode.