Precise measurement of ${\alpha }_K$ and ${\alpha }_T$ for the 39.8-keV $E3$ transition in ${}^{103}\mathrm{Rh}$: Test of internal-conversion theory

Neutron-activated sources of ${}^{103}\mathrm{Ru}$ and ${}^{103}\mathrm{Pd}$ both share the isomeric first-excited state in ${}^{103}\mathrm{Rh}$ as a daughter product. From independent measurements of both decays, we have measured the $K$ shell and total internal-conversion coefficients, ${\alpha }_K$ and ${\alpha }_T$, for the 39.8-keV $E3$ transition, which de-excites that state in ${}^{103}\mathrm{Rh}$, to be 141.1(23) and 1428(13), respectively. When compared with Dirac-Fock calculations, our new results disagree with the version of the theory that ignores the $K$-shell atomic vacancy, which is consistent with our conclusion drawn from a series of measurements on high multipolarity transitions in nuclei with higher $Z$. Calculations that include the atomic vacancy indicate that the transition actually has a small $M4$ component with mixing ratio $\delta =0.023$(5).

Figure 1

Simplified decay schemes for the ${\beta }^{-}$ decay of ${}^{103}\mathrm{Ru}$ and the electron-capture decay of ${}^{103}\mathrm{Pd}$ feeding excited states in their common daughter ${}^{103}\mathrm{Rh}$. Except for the 39.8-keV transition only electromagnetic transitions with $>0.1\%\gamma$-ray intensity are shown. The data are taken from Ref. [22], where numerous weaker transitions are recorded.

Figure 2

Portion of the background-subtracted x- and $\gamma$-ray energy spectrum recorded over a period of 10 days, four months after activation of the Ru/Cu target. This was Run 4. Gamma-ray peaks from the decay of ${}^{103}\mathrm{Ru}$ are labeled by their energy; those from impurities are labeled by their $\beta$-decay parent.

Figure 3

Spectra for the two energy regions of interest in this measurement. (a) and (b) The rhodium $K$ x rays and the $\gamma$-ray peak at 39.8 keV, both taken from the full spectrum presented in Fig. 2 for the Ru/Cu source. (c) The 39.8-keV $\gamma$-ray peak together with europium $K$ x rays from ${}^{153}\mathrm{Gd}$ impurity in our ${\mathrm{RuO}}_2$ source.

Figure 4

Spectrum obtained from the Ru/Cu source as measured with a Si(Li) detector. It shows the rhodium $K$ x rays from the decay of ${}^{103}\mathrm{Ru}$ as well as the ruthenium $K$ x rays that result from fluorescence of the source material.

Figure 5

Plots of the ${\alpha }_K$ and ${\alpha }_T$ results from the seven runs that measured ${}^{103}\mathrm{Ru}$ decay. Only statistical uncertainties are shown. The gray bands represent the averages.

Figure 6

Portion of the background-subtracted x- and $\gamma$-ray energy spectrum recorded over a period of 11.6 days, 10 weeks after activation of the palladium metal foil. Gamma-ray peaks from the decay of ${}^{103}\mathrm{Pd}$ are labeled by their energy; those from impurities are labeled by their $\beta$-decay parent.