\section{Introduction}
Why are we even doing this measurement?
\begin{itemize}
  \item targets for mu-e conversion experiments
  \item why did we measure \ce{W}, \ce{H_2O}, \ldots: background for Xrays of
    interest in Mu2e
  \item existing data? focused on nuclear charge radii, did not report muonic
    X-ray yields. This is true for \ce{^{nat}Ti}~\cite{Wohlfahrt1981}

\end{itemize}