L-Series X-Rays fromπ-Mesonic Atoms

The yields of the $L$-series x-ray lines from $\pi$-mesonic atoms have been measured for fourteen elements between $Z=6\mathrm{} \mathrm{and} 26$. The total yield rises from 18% at carbon to a maximum of about 70% in the vicinity of aluminum, and then decreases. This decrease is caused primarily by nuclear absorption of pions from the $3d$ state; the $3d\to 2p$ yield determinations thus measure the nuclear absorption rate from the $3d$ state. The low-$Z$ drop-off is predicted qualitatively by theoretical calculations of the meson cascade scheme. The observed relative intensities of the different $L$-series emission lines are substantially independent of $Z$ in the range $6\leqq Z\leqq 16$. The $3d\to 2p$ transition energies are consistent with electromagnetically predicted values within the experimental error of 3 to 5% for $Z\le 28$.