SEARCH FOR BETA-BETA-DECAY IN XE-136 - NEW RESULTS FROM THE GOTTHARD EXPERIMENT

The Gotthard Xe experiment has taken an additional 6013 hours of data with an upgraded readout system. Lower limits for the half-life of the double beta decay in Xe-136 are T-1/2(0 nu) > 4.4 x 1023 yr, (includi ng 6830 hours taken in an earlier phase), T-1/2(0 nu chi 0) > 0.72 x 1 0(22) yr and T-1/2(2 nu) > 3.6 x 10(20) yr at 90% confidence level. Al pha spectroscopy, as well as beta alpha and alpha alpha coincidence te chniques lead to a determination of the activity of the gas of 10(-12) g/g effective of Th-232 and U-238. Evaluations of background strongly suggest that an appreciable fraction of the beta beta-candidates come s from the allowed 2 nu decay. (C) 1998 Elsevier Science B.V. All righ ts reserved.