PRECISE DETERMINATION OF RELATIVE AND ABSOLUTE BETA-BETA-DECAY RATES OF TE-128 AND TE-130

Double beta decay of Te-128 has been confirmed and the ratio of half-lives for betabeta decay of Te-130 and Te-128 has been precisely determined as T1/2(130)/T1/2(128) = (3.52 +/- 0.11) x 10(-4) by ion-counting mass spectrometry of Xe in ancient Te ores, using techniques that reduce interferences due to trapped Xe. We have also detected excesses of Xe-126 originating in high energy reactions of cosmic ray muons and their secondaries on Te; such reactions make minor contributions to the measured Xe-128 excesses in the Te ores. The Xe measurements, combined with common Pb dating of the ores , yield a Te-130 half-life of (2.7 +/- 0.1) X 10(21) yr and thus a Te-128 half-life of 7.7 +/- 0.4) x 10(24) yr, the longest radioactive decay lifetime measured to date. These results give limits on the effective Majorana mass of the neutrino (< 1.1 - 1.5 eV) and right-handed currents (\[eta]\ < 5.3 X 10(-8)) comparable to the best obtained from direct neutrinoless betabeta-decay searches. They also imply new limits on unconventional Majorons no constrained by measurements of the Z0 decay width.