Further test of internal-conversion theory with a measurement in ${}^{197}\mathrm{Pt}$

We have measured the $K$-shell internal conversion coefficient, ${\alpha }_K$, for the $346.5$-keV $M4$ transition in ${}^{197}\mathrm{Pt}$ to be $4.23(7)$. This result differs from a previous value, which disagreed significantly from theory. Our new value agrees well with Dirac-Fock calculations and removes the earlier discrepancy as a source of concern.

Figure 1

Percentage differences between the measured and calculated ICCs for two Dirac-Fock calculations: one (a) is without the atomic vacancy and the other (b) is with it included in the “frozen orbital” approximation. The points shown as solid diamonds in both plots correspond to the 20 cases listed by Raman et al. [3] that have better than $2\%$ precision; as indicated at the bottom, five are for $E2$ tranditions, three for $E3$, and the remainder are for $M4$ transitions. The points shown as open circles correspond to our three more-recently measured ${\alpha }_K$ values. For the cases of ${}^{134}\mathrm{Cs}$${}^m$ and ${}^{137}\mathrm{Ba}$ [7, 8] the earlier Raman values are shown in grey; for ${}^{193}\mathrm{Ir}$${}^m$ [5, 6] there was no earlier value with sub-$2\%$ precision.

Figure 2

Abbreviated decay scheme for the decay of ${}^{197}\mathrm{Pt}$${}^m$, showing both its $\gamma$-ray/internal-conversion transition and its $\beta$ decay. Also shown is the $\beta$ decay of the ${}^{197}\mathrm{Pt}$ ground state, which was also produced in this experiment. The $\gamma$ transitions in ${}^{197}\mathrm{Au}$ are grouped according to which $\beta$-decaying state in ${}^{197}\mathrm{Pt}$ feeds them. The group of three on the left corresponds to the ${}^{197}\mathrm{Pt}$ ground-state decay; the group of five on the right corresponds to the isomeric-state decay. The dashed arrows represent very weak $\gamma$ rays. All the information is taken from Ref.[14].

Figure 3

Portions of the first spectrum collected after activation, covering the two energy regions of interest in the determination of the ${\alpha }_K$ ratio for the 346.5-kev transition in ${}^{197}\mathrm{Pt}$: (a) the overlapping platinum and gold $K_{\alpha }$ x rays together with the 77.35-keV $\gamma$ ray from ${}^{197}\mathrm{Au}$, which masks the $K_{\beta }$ x rays; (b) the 346.5-keV $\gamma$ ray.

Figure 4

Portion of the $\gamma$-ray energy spectrum measured 6 h after the spectrum shown in Fig.3. Peaks are identified by their $\beta$-decay parent except for the 346.5-keV peak, which is due to the isomeric transition from ${}^{197}\mathrm{Pt}$${}^m$.

Figure 5

All three panels present plots of decay rates as a function of time: (a) gives the rates obtained with the total, background-subtracted counts in the energy region of the $K$ x rays (solid circles), together with the same results after further subtraction of the impurity contributions listed in Table (open squares); (b) shows an expanded view of the first ten after-subtraction results from the top panel (again plotted as open squares). On the same expanded time scale, (c) presents (as solid squares) the results for the $K$ x rays from ${}^{197}\mathrm{Pt}$${}^m$ as obtained from a two-component fit to the composite decay in the middle and top panels. The corrected decay rates of the 346.5-keV $\gamma$ ray from ${}^{197}\mathrm{Pt}$${}^m$ are also plotted (as solid triangles) in the bottom panel. Where no uncertainties are visible, they are smaller than the data points. All curves are computer fits with half-lives fixed to known values.

Figure 6

The same plot as in Fig.1 except that the results from the present work, for ${}^{197}\mathrm{Pt}$${}^m$, have been added as open circles. The previous values, which were listed by Raman et al. [3], are shown in grey.