Negative-muon capture in ionic compounds and some related elements

Relative muon capture probabilities for the individual elements of compounds and relative muonic x-ray intensities have been measured for a series of ionic solids and some related elements. Marked similarities are observed in relative $K$- and $L$-series intensities of a single ionic species, independent of bond partner (e.g., ${\mathrm{Cl}}^{-}$ in NaCl and Ca${\mathrm{Cl}}_2$). However, significant $K$-series differences are observed for an element in an ionic vs a covalent situation (e.g., Cl in NaCl and in NaCl${\mathrm{O}}_4$), with the higher $K$ x rays from the covalently bound element showing relative enhancements of as much as a factor of 2 over the ion. The measured intensities have been compared to the predictions of a meson cascade code, which allows variation in the muon initial principal quantum number ($N_{\mu }$) and the parameter $\alpha$ in the commonly used modified statistical angular momentum distribution, $P\left(l\right)=(2l+1)\mathrm{}{e}^{\alpha l}$. The fit was quite insensitive to the choice of $N_{\mu }$ (in the neighborhood $N_{\mu }=17\mathrm{}$), but the results could not be well fitted with a single value of $\alpha$. The atomic capture probabilities predicted by recent calculations do not fit the data noticeably better than the Fermi-Teller "$Z$ law."