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Register a new userPrecision half-life measurement of the boldmath$beta^+$ decay of tsups{37}K
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The half-life of tsups{37}K has been measured to be $1.23651(94)~mathrm{s}$, a value nearly an order of magnitude more precise than the best previously reported. The $beta^+$ decay of tsups{37}K occurs mainly via a superallowed branch to the ground-state of its $T=1/2$ mirror, tsups{37}Ar. This transition has been used recently, together with similar transitions from four other nuclei, as an alternative test of CVC and method for determining $V_{ud}$, but the precision of its $ft$ value was limited by the relatively large half-life uncertainty. Our result corrects that situation. Another motivation for improving the $ft$ value was to determine the standard-model prediction for the $beta$-decay correlation parameters, which will be compared to those currently being measured by the trinat{} collaboration at triumf. The new $ft$ value, $4605(8)~mathrm{s}$, is now limited in precision by the $97.99(14)%$ ground-state branching ratio.
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Using TRIUMFs neutral atom trap, TRINAT, for nuclear $beta$ decay, we have measured the $beta$ asymmetry with respect to the initial nuclear spin in $^{37}mathrm{K}$ to be $A_beta=-0.5707(13)_mathrm{syst}(13)_mathrm{stat}(5)_mathrm{pol}$, a 0.3% measurement. This is the best relative accuracy of any $beta$-asymmetry measurement in a nucleus or the neutron, and is in agreement with the standard model prediction $-0.5706(7)$. We compare constraints on physics beyond the standard model with other $beta$-decay measurements, and improve the value of $V_mathrm{ud}$ measured in this mirror nucleus by a factor of 4.
A high-precision half-life measurement for the superallowed Fermi $beta^+$ emitter $^{22}$Mg was performed at the TRIUMF-ISAC facility using a 4$pi$ proportional gas counter. The result of $T_{1/2} = 3.87400 pm 0.00079$ s is a factor of 3 more precise than the previously adopted world average and resolves a discrepancy between the two previously published $^{22}$Mg half-life measurements.
This Letter reports results from the NEMO-3 experiment based on an exposure of 1275 days with 661g of 130Te in the form of enriched and natural tellurium foils. The double beta decay rate of 130Te is found to be greater than zero with a significance of 7.7 standard deviations and the half-life is measured to be T1/2 = (7.0 +/- 0.9(stat) +/- 1.1(syst)) x 10^{20} yr. This represents the most precise measurement of this half-life yet published and the first real-time observation of this decay.
The beta-decay half-life of 62Ga has been studied with high precision using on-line mass separated samples. The decay of 62Ga which is dominated by a 0+ to 0+ transition to the ground state of 62Zn yields a half-life of T_{1/2} = 116.19(4) ms. This result is more precise than any previous measurement by about a factor of four or more. The present value is in agreement with older literature values, but slightly disagrees with a recent measurement. We determine an error weighted average value of all experimental half-lives of 116.18(4) ms.
We have measured the half-life of the superallowed 0+ -to- 0+ beta+ emitter 26Si to be 2245.3(7) ms. We used pure sources of 26Si and employed a high-efficiency gas counter, which was sensitive to positrons from both this nuclide and its daughter 26mAl. The data were analyzed as a linked parent-daughter decay. To contribute meaningfully to any test of the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, the ft value of a superallowed transition must be determined to a precision of 0.1% or better. With a precision of 0.03% the present result is more than sufficient to be compatable with that requirement. Only the branching ratio now remains to be measured precisely before a +/-0.1% ft value can be obtained for the superallowed transition from 26Si.
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