Weak decay of 130 Ba and 132 Ba : Geochemical measurements

The half-life of 130Ba due to multichannel weak decay (2β+, 2EC, and ECβ+) has been determined for the first time by the measurement of the 130Xe daughter accumulated in natural barite (BaSO4) from the Belorechenskoe deposit in North Caucasus, Russia. The accumulation time was determined from U-Xe and K-Ar gas-retention ages measured in the same material, yielding a half-life for 130Ba for all weak decay modes of 2.2±0.5×1021yr (68% C.L.), about a factor of 2 lower than that predicted by the proton-neutron quasiparticle random phase approximation. From excess 132Xe observed in this barite, the half-life for weak decay of 132Ba can be estimated (T1/2=1.3±0.9×1021yr). However, this value is more tentative, since other sources of this isotope cannot be excluded, but the lower limit of 2.2×1021yr remains firm.