Magnetic-substate ionization of medium- and high-Zt elements induced by proton impact

Abstract

Magnetic-substate ionization of $L_3$-subshell and the consequent atomic alignment of molybdenum, cadmium, indium and gold ions are reported for proton impact with low incident velocity range (0.147∼0.232)$v_{L_3}$, (0.124∼0.196)$v_{L_3}$, (0.120∼0.191)$v_{L_3}$, (0.067∼0.107)$v_{L_3}$, respectively. Here, $v_{L_3}$ is the classical orbital velocity of an electron in the $L_3$-subshell of the target atom. It is demonstrated that the $L_{\beta 2}$ and $L_{\alpha }$ X-ray lines present spatially non-isotropic emission. Coster-Kronig calibration factors as well as anisotropy coefficients are calculated to derive the alignment parameter $A_{20}$. Unifying $A_{20}$ and the cross section ${\sigma }_{L_3}$ in direct ionization, a novel methodology to determine the cross sections $\sigma (\frac{3}{2},\frac{1}{2})$ and $\sigma (\frac{3}{2},\frac{3}{2})$ for magnetic substate ionization is introduced. The results manifest that both cross sections exhibit positive correlation with the incident energy and inverse correlation with atomic number of the target. The cross section $\sigma (\frac{3}{2},\frac{1}{2})$ is found to be greater than $\sigma (\frac{3}{2},\frac{3}{2})$, and the tendency of the ratio $\frac{\sigma (\frac{3}{2},\frac{1}{2})}{\sigma (\frac{3}{2},\frac{3}{2})}$ varies regularly and gradually as the atomic number increases for the four targets. Particularly, it also implies that the ionization cross section for high-$Z_t$ targets exhibits a more remarkable increase rate with the increase of incident energy. Experimental results are well understood by taking account of probability density distribution of the orbital electrons.