Precise measurement of the β decay and electron capture of ${}^{22}\mathrm{Na}$, ${}^{198}\mathrm{Au}$, and ${}^{196}\mathrm{Au}$ in low-temperature metal hosts, and reexamination of lifetime modifications

We investigated half-life changes with temperature of ${}^{22}\mathrm{Na}$ embedded in Al and ${}^{198}\mathrm{Au}$/${}^{196}\mathrm{Au}$ embedded in Au. We do not find any change of the half-life between room temperature and 10 K on the level of 0.04% for ${}^{22}\mathrm{Na}$, 0.03% for ${}^{198}\mathrm{Au}$, and 0.5% for ${}^{196}\mathrm{Au}$ in striking disagreement with the first experimental works and predictions. Additionally, the absolute half-life for ${}^{198}\mathrm{Au}$ has been determined to $2.6937\pm 0.0003$ d which is 5 standard deviations below the recommended NIST value but in agreement with other high-precision measurements.

Figure 1

Screening enhancement vs screening energy $U_e$ for the ${}^{22}\mathrm{Na}$ ${\beta }^{+}$ decay. The screening model of Durand [19] should be taken for high screening energies.

Figure 2

Enhancement of the ${}^{22}\mathrm{Na}$ ${\beta }^{+}$ decay rate vs temperature. See also Fig. 1.

Figure 3

Schematic view of the experimental setup. The cryopump cooling the sample is situated between two HPGe detectors of 100% relative efficiency. All items were fixed on a common plate mounted on a stand.

Figure 4

Counting rate of the ${}^{22}\mathrm{Na}$ ${\beta }^{+}$ decay $\gamma$-rays relative to the ${}^{60}\mathrm{Co}$ $\gamma$-ray rate, summed over both detectors. The vertical bars represent the statistical error, the horizontal bars the integration time. The temperature is also shown (right axis). The dashed lines are fits to the data points at room temperature (red circles) and at $T\approx$ 10 K (blue squares) with the half-life of the ratio ${}^{22}\mathrm{Na}$ / ${}^{60}\mathrm{Co}$ fixed to the literature value. If not fixed, the resulting half-life of ${}^{22}\mathrm{Na}$ is $2.57\pm 0.13$ yr, in agreement with the literature value [24] of 2.60 yr.

Figure 5

Decrease of the 412-keV ${}^{198}\mathrm{Au}$ $\gamma$-ray intensity at room temperature and at 10 K, relative to the half-life corrected $\gamma$-ray intensities of ${}^{133}\mathrm{Ba}$ and ${}^{137}\mathrm{Cs}$. Each point corresponds to a 10-min integration interval. The normalized data points (big circles) from the previously reported longer half-life [7] and the corresponding calculated decay curve (dashed) is also indicated and clearly disagrees with our data.

Figure 6

Precise (error < 0.005 d) measurements of the ${}^{198}\mathrm{Au}$ half-life since 1969, see Table .