Systematics of target and projectileK-x-ray production and radiative electron capture for 20-80-MeVClq+ions incident on 25-200-μg/cm2Cu targets

Abstract

A systematic investigation of $K$-x-ray production for 20-80-MeV Cl ions in collision with thin self-supporting Cu targets has been conducted. Target and projectile characteristic x rays and radiative electron capture (REC) have been measured as a function of target thickness for incident charge states $ql{Z}_{1}\ensuremath{-}2$. At 80 MeV data were also obtained for $q={Z}_{1}\ensuremath{-}1$. Large enhancements in both characteristic x-ray production and REC were observed for $q={Z}_{1}\ensuremath{-}1$. Measured x-ray yields were parametrized versus target thickness using the model of Betz et al., and least-squares fits to the data were performed. Target $K$-x-ray production for $ql{Z}_{1}\ensuremath{-}2$ is described reasonably well by the Coulomb perturbed-stationary-state relativistic plus electron capture relativistic (CPSSR+ECR) theory. For $q={Z}_{1}\ensuremath{-}1$ the enhancement in the x-ray yield is predicted quite well by the method of Gray et al. The mean fluorescence yield for the highly stripped Cl ions is determined and found to increase by a factor of about 6 over the range 20-80 MeV, having a value (\ensuremath{\sim} 0.1) nearly equal to the single $K$-vacancy value at 20 MeV. The radiative lifetime for the projectile ions is found to be \ensuremath{\sim} 3 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}14}$ sec, which is about three times longer than the single-$K$-vacancy radiative lifetime calculated by Scofield. Parametrization of the REC yields versus target thickness is used to normalize the measured REC intensity to the fraction of ions with $K$ vacancies. Resulting REC cross sections are compared with the free-electron theory of Bethe and Salpeter and good agreement is obtained if it is assumed that each of the loosely bound electrons in Cu contributes equally to the REC process. By combining the results obtained for the characteristic x rays and REC, the fluorescence yield for $K$-shell capture events may be estimated, giving values in the range (2-4) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$ for the beam energies studied.