Precise measurement of ${\alpha }_K$ and ${\alpha }_T$ for the 109.3-keV $M4$ transition in ${}^{125}\mathrm{Te}$: Test of internal-conversion theory

We have measured the $K$-shell and total internal conversion coefficients (ICCs), ${\alpha }_K$ and ${\alpha }_T$, for the 109.3-keV $M4$ transition in ${}^{125}\mathrm{Te}$ to be 185.0(40) and 350.0(38), respectively. Previously this transition's ICCs were considered to be anomalous, with measured values lying below calculated ones. When compared with Dirac-Fock calculations, our new results show good agreement. The ${\alpha }_K$ result agrees well with the version of the theory that takes account of the $K$-shell atomic vacancy and disagrees with the one that does not. This is consistent with our conclusion drawn from a series of measurements on high multipolarity transitions.

Figure 1

Decay scheme for the 57-d isomer in ${}^{125}\mathrm{Te}$, illustrating the channels important to this measurement. The data are taken from Ref. [25].

Figure 2

Portion of the background-subtracted x- and $\gamma$-ray energy spectrum recorded over a period of 4.7 d, three weeks after activation of enriched ${}^{124}\mathrm{Te}$. Peaks are labeled by their $\beta$-decay parent. The cluster of “sum peaks” around 60 keV arise from summing of $K$ x rays and $\gamma$ rays from the 35.5-keV transition with $K$ x rays from the 109-keV transition. The labeled Ge escape peaks are associated with this cluster.

Figure 3

Spectra for the two energy regions of interest in this measurement, the one on the left including the tellurium $K$ x rays with the 35.5-keV $\gamma$-ray peak; and the one on the right, the $\gamma$-ray peak at 109.3 keV. These correspond to the full spectrum presented in Fig. 2.