L-shell ionization in near-central collisions of heavy ions with low-Zatoms

Abstract

The K␣ x-ray emission spectra of Ca, Ti, Cr, and Fe targets bombarded by 2-19-MeV/amu C, O, and Ne ions were measured by means of high-resolution crystal diffractometry. The KL N x-ray satellite lines appearing in these spectra as a result of the radiative decay of atomic states with one hole in the K shell and N in the L subshells could be resolved, and their relative intensities determined. The latter were corrected to account for the intra-atomic rearrangement processes preceding the K x-ray emission. From the values obtained the heavy ion induced L-shell vacancy distribution was then deduced for each collision. Significant deviations from the binomial distribution were observed. The discrepancies could be slightly diminished by assuming that the L-shell vacancy production is due to two uncorrelated processes: direct Coulomb ionization and target L-shell electron capture into the projectile K shell. A new KL N vacancy yield distribution model based on statistical considerations was built, which takes into account both mechanisms of vacancy production. The average direct L-shell ionization probabilities per electron related to the investigated collisions were determined by fitting this distribution to the corrected experimental L vacancy yields, employing results of three-body classical trajectory Monte Carlo ͑CTMC͒ calculations for the electron capture probabilities. The so-obtained direct ionization probabilities were found to be somewhat smaller than the ones deduced from the standard binomial distribution, especially in low-energy collisions for which electron capture is more important. It was furthermore observed that CTMC calculations significantly overestimate the direct ionization probabilities found in the present experiment. To a smaller extent, the same holds for the geometrical model predictions, whereas theoretical results from the semiclassical approximation model were found to reproduce the experimental data better.

M shell ionization of Ar induced in near-central collisions with MeV protons

“…The validity of the independent-electron approximation for the description of multiple inner-shell ionization was discussed in these works. More recent studies addressing L shell ionization of low and mid-Z atoms in collisions with light [13][14][15][16] and heavy ions [17][18][19] put a lot of effort into extracting original vacancy yields by taking into account the effects of rearrangement of the inner-shell vacancies prior to x-ray emission as well as changes in the fluorescence yield due to multiply ionized states. These primary vacancy yield were then used to extract accurate L shell ionization probabilities, which were compared extensively to various theoretical predictions.…”

A wide-band, high-resolution vacuum flat crystal spectrometer for LEAF facility

“…However, the formation of 𝐾-shell hollow atoms by ion-atom collisions is frequently accompanied by the generation of spectator vacancies in the 𝐿 or higher shells, resulting in a multiplex angular momentum coupling scheme and diverse binding energies of the transition electrons, leading to changes in transition energy, intensity ratio, and fluorescence yield of x-rays [20]. For example, each spectator 𝐿-shell vacancy of argon ions enhances the 𝐾𝛼 ℎ and 𝐾𝛼𝛼 energy by about 20 eV and 40 eV, respectively [21].…”

Structure of single KL0–, double KL1–, and triple KL2 − ionization in Mg, Al, and Si targets induced by photons, and their absorption spectra

“…The study of the satellite lines is extremely cru-cial in atomic physics, since they provide information on excitation dynamics, relaxation, and other effects that influence the x-ray emission process. Regarding K transitions, several works were carried out to investigate satellite emissions induced by photon [1][2][3][4][5][6][7][8][9][10][11][12][13][14], proton and heavy-ion [15][16][17][18][19][20][21][22][23][24][25], and electron [26][27][28][29][30][31][32][33][34] impact, although most of them were focused on a few particular elements or transitions.…”