The 198Au βhalf-life in the metal Au⋆

Measurement of the half-life ofAu198in a nonmetal: High-precision measurement shows no host-material dependence

“…We established that the difference between the half-lives measured in an insulator and in a conductor is less than 0.04%, with a confidence level of 68% (one standard deviation). This limit is more than two orders of magnitude lower than the 7% difference predicted by the "Debye plasma model" [3]. Our result, together with previous measurements of ours [4,11] and others [12], effectively refutes all the predictions of the Debye plasma model as they apply to β − , β + and electron-capture decays; and also contradicts the measurements that initially supported those predictions [2,3,13].…”

Half-life of the electron-capture decay ofRu97: Precision measurement shows no temperature dependence

“…Since the maximum decay energy for any allowed transition from 97 Ru is 892 keV, the nucleus must decay by pure electron capture. Three years ago, Wang et al [6] reported half-life measurements of another pure electron-capture emitter, 7 Be, situated in both palladium and indium metals, in which they observed differences of 0.9(2)% and 0.7(2)%, respectively, between room temperature and 12 K. The same group also reported cases of temperature dependence for α, β − , and β + decay modes [3][4][5] and interpreted them all as the result of a "Debye plasma," which purportedly acts in any metal host and leads to a smooth dependence of half-lives on temperature. In that context, their result for 7 Be decay was understood to be the indication of a generic property of all ec decays rather than a unique property of 7 Be.…”

“…Quite recently, however, measurements have been reported claiming relatively large changes in half-lives for α, β − , β + , and ec decays depending on whether the radioactive parent was placed in an insulating or conducting host material, and whether the latter was at room temperature or cooled to 12 K. Specifically, 210 Po, an α emitter, when implanted in copper was reported to exhibit a half-life shorter by 6.3(14)% at 12 K than at room temperature [3]; the β − emitter 198 Au in a gold host reportedly had a half-life longer by 3.6(10)% at 12 K [4]; 22 Na, which decays predominantly (90%) by β + emission, was measured as having a 1.2(2)% shorter half-life at 12 K [5]; and 7 Be, which decays by pure electron capture, apparently had a half-life longer by 0.9(2)% at 12 K in palladium and by 0.7(2)% in indium [6]. The authors of these reports also proposed a theoretical explanation of their observations based on quasifree electrons-a "Debye plasma"-causing an enhanced screening effect in metallic hosts.…”

“…Of greatest concern to us were the half-lives of superallowed 0 + → 0 + β + transitions, essential to fundamental tests of the standard model [8]. Their precision has typically been quoted to less than 0.05%, well below the temperature and host-material dependence claimed by the new measurements [3][4][5][6].…”

“…While the original measurement by Spillane et al [4] followed the decay for only a little over one half-life, we recorded the decay with much better statistics for over ten half-lives at both room temperature and at 19 K. Our results showed the half-lives at the two temperatures to be the same within 0.04%, a limit two orders of magnitude less than the difference claimed by Spillane et al This null result was subsequently confirmed by two other measurements of 198 Au, which set limits of 0.13% in a Al-Au alloy host [10] and 0.03% in gold [11]. The latter reference also reported a new 22 Na decay measurement, which set an upper limit on the temperature dependence of that β + decay at 0.04%, again nearly two orders of magnitude below the earlier claim, in this case by Limata et al [5].…”