Weak decay of130Baand132Ba: Geochemical measurements

Abstract

The half-life of 130 Ba due to multichannel weak decay ͑2␤ ϩ , 2EC, and EC␤ ϩ ͒ has been determined for the first time by the measurement of the 130 Xe daughter accumulated in natural barite (BaSO 4 ) 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 130 Ba for all weak decay modes of 2.2Ϯ0.5ϫ10 21 yr ͑68% C.L.͒, about a factor of 2 lower than that predicted by the proton-neutron quasiparticle random phase approximation. From excess 132 Xe observed in this barite, the half-life for weak decay of 132 Ba can be estimated (T 1/2 ϭ1.3Ϯ0.9ϫ10 21 yr). However, this value is more tentative, since other sources of this isotope cannot be excluded, but the lower limit of 2.2ϫ10 21 yr remains firm.Te(33.87%) and Ba is present in minerals most abundantly as BaSO 4 whereas Te is often found as the pure native metal. This implies that, in order to detect a similar half-lives with Ba and Te samples of the same antiquity, it would take 500 times more barite than native tellurium. This means that interferences and background of trapped atmospheric xenon, which are both normally proportional to sample mass, will PHYSICAL REVIEW C, VOLUME 64, 035205

Weak Decay of Tellurium and Barium Isotopes in Geological Samples: Current Status

“…The confidence interval (95%) at this intercept provides the upper limit for the amount of 130 Xe from weak decay of 130 Ba and corresponds to the lower limit of the 130 Ba half-life estimate: > 2.4×10 21 yr. This limit turns out to be in agreement with the 130 Ba half-life of (2.2 ± 0.5)×10 21 yr [13] and ~ 2.1×10 21 yr [12].…”

“…The first positive observation of 130 Ba in natural barite yielded a half-life of (2.2 ± 0.5)×10 21 yr (68% C.L.) [13]. Later based on analyses of an Archean barite a 3.4 times shorter value was reported (6.0 ± 1.1×10 20 yr [14]).…”

“…There are volcanogenic barites, which might be better shielded from cosmic rays and we are currently looking for these samples to verify the only available 130 Ba half-life measurement [13] that is not compromised by the high energy cosmic-ray interactions.…”

Search for two-neutrino double electron capture of Xe124 with XENON100

“…A measurement of the 2ν2EC half-life would help to test the accuracy of these models. So far, 2ν2EC has only been observed for 130 Ba in geochemical experiments [8,9]. In addition, there is an indication for 2ν2EC of 78 Kr from a low-background proportional counter [10].…”

Radioactive contamination of BaF2crystal scintillator

“…Natural barium contains two potentially 2 active isotopes, 130 Ba (Q 2 = 2618.7(2.6) keV) and 132 Ba (Q 2 = 844.0(1.1) keV) [5,6]. The 130 Ba isotope is of particular interest because of the reports on the observation in geochemical experiments of double electron capture with a half-life T 1/2 = (2.2 ± 0.5)  10 21 yr [7] and T 1/2 = (6.0 ± 1.1)  10 20 yr [8].…”