Precise measurement of<i>K</i>-shell fluorescence yield in iridium: An improved test of internal-conversion theory

Abstract

We have measured the total intensity of K x rays relative to 129.4-keV \ensuremath{\gamma} rays from decay of the second excited state in $^{191}\mathrm{Ir}$. This ($M1+E2$) transition was observed following the \ensuremath{\beta} decay of 15.4-d $^{191}\mathrm{Os}$. Our measured ratio yields the result ${\ensuremath{\alpha}}_{K}{\ensuremath{\omega}}_{K}=2.044(11)$. When combined with a recent measurement of the same ratio for the 80.2-keV $M4$ transition from $^{193}\mathrm{Ir}{}^{m}$, this result strongly confirms the need for the K-shell hole to be included in calculations of internal-conversion coefficients ${\ensuremath{\alpha}}_{K}$. Since the ${\ensuremath{\alpha}}_{K}$ value calculated for the $^{191}\mathrm{Ir}$ transition is virtually independent of the hole treatment, our result also yields a model-independent value for the iridium fluorescence yield, ${\ensuremath{\omega}}_{K}=0.954(9)$.