No abstract

No 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

One of the major goals of the Genesis Mission was to refine our knowledge of the isotopic composition of the heavy noble gases in solar wind and, by inference, the Sun, which represents the initial composition of the solar system. This has now been achieved with permil precision: 36 124 Xe/ 132 Xe = .00491 ± .00007 (error-weighted averages of all published data). The Kr and Xe ratios measured in the Genesis solar wind collectors generally agree with the less precise values obtained from lunar soils and breccias, which have accumulated solar wind over hundreds of millions of years, suggesting little if any temporal variability of the isotopic composition of solar wind krypton and xenon. The higher precision for the initial composition of the heavy noble gases in the solar system allows (1) to confirm that, exept 136 Xe and 134 Xe, the mathematically derived U-Xe is equivalent to Solar Wind Xe and (2) to provide an opportunity for better understanding the relationship between the starting composition and Xe-Q (and Q-Kr), the dominant current "planetary" component, and its host, the mysterious phase-Q.

No abstract

No abstract

Double beta decay of '2'Te has been confirmed and the ratio of half-lives for pp decay of " Te and Te has been precisely determined as Tl&2/T',~&=(3.52+0. 11)X10 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 originating in high energy reactions of cosmic ray muons and their secondaries on Te; such reactions make minor contributions to the measured ' Xe excesses in the Te ores. The Xe measurements, combined with common Pb dating of the ores, yield a ' Te half-life of (2.7+0. 1)X 10 ' yr and thus a ' Te half-life of (7.7+0.4) X 10 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 (~(g )~( 5.3 X 10 ') comparable to the best obtained from direct neutrinoless PP-decay searches. They also imply new limits on unconventional Majorons not constrained by measurements of the Z decay width. PACS number(s): 23.40.8w, 14.60.Gh, 14.80.Gt, 27.60.+j PRECISE DETERMINATION OF RELATIVE AND ABSOLUTE. . . 807 T0( m ) to T0 ( m ), where ( m ) is the effective Majorana mass of the neutrino [4,5]. This implies that the relative contribution of Ov /3P decay to the ' Te decay (TQ =0.87 MeV) is much larger than that for ' Te (T0 =2.53 MeV) for values of ( m ) near the current limits of a few eV. The experimental advantage of the Te system is that both of the daughters of the Te PP decay, Xe and ' Xe, are noble gases which can be easily extracted from Te ores. Their ratio, ' Xe/' Xe, is directly proportional to the ratio of decay rates I' /I', and can be determined with relatively high precision by noble-gas mass spectrometry, thus eliminating many sources of systematic error. These advantages provided by the Te system have prompted many groups to study it, and although the decay of ' Te is well established, there has been a longstanding controversy over whether PP decay of ' Te has actually been observed. Several studies by the University

No abstract