Measurement of the half-life of 198Au in a non-metal: High-precision measurement shows no host-material dependence

We have measured the half-life of the beta decay of 198Au to be 2.6948(9) d, with the nuclide sited in an insulating environment. Comparing this result with the half-life we measured previously with a metallic environment, we find the half-lives in both environments to be the same within 0.04%, thus contradicting a prediction that screening from a "plasma" of quasi-free electrons in a metal increases the half-life by as much as 7%

Branching ratios for the beta decay of 21Na

We have measured the beta-decay branching ratio for the transition from 21Na to the first excited state of 21Ne. A recently published test of the standard model, which was based on a measurement of the beta-nu correlation in the decay of 21Na, depended on this branching ratio. However, until now only relatively imprecise (and, in some cases, contradictory) values existed for it. Our new result, 4.74(4)%, reduces but does not remove the reported discrepancy with the standard model.Comment: Revtex4, 2 fig

Experimental Validation of the Largest Calculated Isospin-Symmetry-Breaking Effect in a Superallowed Fermi Decay

A precision measurement of the gamma yields following the beta decay of 32Cl has determined its isobaric analogue branch to be (22.47^{+0.21}_{-0.19})%. Since it is an almost pure Fermi decay, we can also determine the amount of isospin-symmetry breaking in this superallowed transition. We find a very large value, delta_C=5.3(9)%, in agreement with a shell-model calculation. This result sets a benchmark for isospin-symmetry-breaking calculations and lends support for similarly-calculated, yet smaller, corrections that are currently applied to 0+ -> 0+ transitions for tests of the Standard Model

Precise measurement of K-shell fluorescence yield in iridium: An improved test of internal-conversion theory

Journals published by the American Physical Society can be found at http://publish.aps.org/We have measured the total intensity of K x rays relative to 129.4-keV gamma rays from decay of the second excited state in Ir-191. This (M1+E2) transition was observed following the beta decay of 15.4-d Os-191. Our measured ratio yields the result alpha(K)omega(K)=2.044(11). When combined with a recent measurement of the same ratio for the 80.2-keV M4 transition from Ir-193(m), this result strongly confirms the need for the K-shell hole to be included in calculations of internal-conversion coefficients alpha(K). Since the alpha(K) value calculated for the Ir-191 transition is virtually independent of the hole treatment, our result also yields a model-independent value for the iridium fluorescence yield, omega(K)=0.954(9)