Results of a search for 2β decay of 136Xe with high-pressure copper proportional counters in Baksan Neutrino Observatory

A search for 2 beta decay of Xe-136 with two high-pressure copper proportional counters was carried out in the Baksan Neutrino Observatory. The experiment is based on comparison of spectra measured with natural and enriched xenon. No evidence was found for 2 beta(2 nu) and 2 beta(0 nu) decay. The decay half-life limit based on data measured for 8000 h is T-1/2 >= 8.5 x 10(21) yr for 2 nu. mode and T-1/2 >= 3.1 x 10(23) yr for 0 nu mode (90% C.L.).