X-ray emission from foil-excited chlorine beams

Abstract

Metastable $K$-x-ray emitters produced in foil excitation of chlorine beams between 23 and 55 MeV have been observed and their production probabilities surveyed over this energy range. Using coincidence techniques, we find that the emitters belong primarily to the helium- and lithiumlike components in the post-foil beam. A search for x-ray emission from systems with more than three electrons has been made and is discussed. The major emitting states have been identified as the $(1s2p)^{3}P_{2}$ and $(1s2s2p)^{4}P_{\frac{5}{2}}$ states in helium- and lithiumlike chlorine whose radiative decay is magnetic quadrupole. Using both coincidence techniques and a doppler-tuned x-ray spectrometer, we have measured the lifetimes and binding energies of these states. The lifetime of the $2^{3}P_{2}$ state is in good agreement with theory, while the binding energies show the importance of relativistic contributions in the theory. A long-lived component of the excited beam is identified as coming from the $1^{1}S_{0}\ensuremath{\leftarrow}2^{3}S_{1}$ decay. A lifetime of 280 \ifmmode\pm\else\textpm\fi{} 25 nsec has been measured for this state, shorter than the theoretical $M1$ lifetime of 381 nsec.