Precise measurement of ${\alpha }_K$ for the 88.2-keV $M4$ transition in ${}^{127}\mathrm{Te}$: Test of internal-conversion theory

We have measured the $K$-shell internal conversion coefficient, ${\alpha }_K$, for the 88.2-keV $M4$ transition from the 106-day isomer to the ground state in ${}^{127}\mathrm{Te}$ to be 484(6). When compared with Dirac-Fock calculations of ${\alpha }_K$, this result agrees well with the version of the theory that incorporates the effect of the $K$-shell atomic vacancy and disagrees with the one that does not. As a byproduct of this measurement, we have determined the $\beta$ branching from the isomer to be 2.14(3)%.

Figure 1

Decay scheme for the 106-day isomer in ${}^{127}\mathrm{Te}$, illustrating the channels important to this measurement. The data are taken from Ref. [16] except for the $\beta$ branching ratio from the isomeric state and the $\gamma$ branching of the 418.0 keV level, which reflect new results from this work.

Figure 2

Portion of the background-subtracted x- and $\gamma$-ray energy spectrum recorded over a period of two weeks, more than a month after activation of enriched ${}^{126}\mathrm{Te}$. Peaks are labeled by their $\beta$-decay parent. The inverted “peak” at 352 keV results from a subtracted background $\gamma$ ray present in the decay of ${}^{214}\mathrm{Pb}$, which is a granddaughter of environmental ${}^{222}\mathrm{Rn}$ and consequently is not constant in time.

Figure 3

Spectra for the two energy regions of interest in this measurement, the one on the left including the tellurium $K$ x rays and the one on the right, the $\gamma$-ray peak at 88.2 keV. These correspond to the full spectrum presented in Fig. 2.