Energy shifts and relative intensities of K X-rays produced in fast heavy charged particle collisions

Abstract

Current theories of inner-shell ionization in fast ion-atom collisions have been reviews and a simplified classical treatment for multiple inner-shell ionization by Coulomb excitation, based upon the binary encounter model, has been developed. The probability of simultaneous K-plus-L-shell ionization in collisions between Ca, Ti, Fe, and Cu target atoms and fast deuterons, alpha particles, and carbon ions has been investigated. The results show that the fraction of K?? x-rays emitted in the presence of an L-shell vacancy (a) decreases with increasing projectile velocity above a projectile to L-shell electron velocity ration 1, (b) decreases with increasing target atomic number, and (c) increases with projectile charge. The projectile velocity dependence is in fairly good agreement with the simplified classical multiple ionization model. Systematic measurements of the dependence of K??/K?? x-ray intensity rations on target atomic number (19 [less than or equal to] Z [less than or equal to] 47), and on the projectile energy and charge have been carried out. The results were compared with Hartree-Fock-Slater calculations of radiative transition probabilities and found to be consistent with the intensity ratios expected for atoms multiply ionized in the L- and M-shells. Using the information obtained on simultaneous K-plus-L-shell ionization, the energy dependence of the simultaneous M-shell ionization probability was deduced and found to be in good agreement with the simplified classical multiple ionization model. Fission fragments from the spontaneous fission of ???ü???Cf were used to study x-ray spectra for ion-atom collisions involving very heavy projectiles. Spectral measurements of K, Ni, and Br K x-rays and Au L x-rays were carried out and compared with spectra resulting from excitation by alpha particles and photons. The large energy shifts and relative intensity differences observed in the fission fragment excited spectra are similar in character to those observed in fast carbon ion bombardments. Multiple L- and M-shell vacancy configurations together with high ionic charge states are required to reproduce the measured x-ray energy shifts with HFS calculations.