The Half-life of 130Te Double β-decay

Abstract

In order to determine the half-life of the 130Te double β-decay, the amounts and isotopic composition of xenon extracted from tellurium ores, from the Oya gold mine in Japan, have been measured with a high-sensitivity mass spectrometer. Compared with atmospheric xenon an excess was definitely found at mass numbers 129, 130 and 131 in the extracted xenon. The excess of 130Xe is predominant, the average amount in three samples being (1.32 ± 0.09) × 10-11 ccSTP/g 130Te. Attributing the excess 130Xe to the double β-decay of 130Te, the half-life is estimated to be (8.20 ± 0.64) × 1020 years, assuming an age of (9.06 ± 0.29) × 107 years for the Te ores. The latter value is the K-Ar age of porphyrite, which is in close geological connection with the Te ores. In order to investigate the other excesses than that of 130Xe, isotopic analyses were also carried out on Xe from three other Te ores from the same mine. The ratios (129Xe/131Xe) excess=1.58 and (129Xe/130Xe) excess = 2.1 were found to be the same for all samples. The origin of these excesses is discussed. In addition a small excess of 128Xe was found. If this is attributed to 128Te double β-decay, the half-life of 128Te is estimated to be 3 × 1022 years, a value shorter by about three orders of magnitude than the theoretically expected half-life. The above estimated half-life may be a lower limit of the 128Te half-life. The general tendency of the isotopic abundances (except for the above excesses), of the xenon extracted from Te ores seems to be to slightly increase in excess as one moves toward the lighter isotopes (as compared with atmospheric xenon).