H. Tawara

Coster-Kronig electrons from the autoionizing Rydberg states of 2 MeV u(-1) Si5+ ions excited through a thin C-foil target

Several peaks have been observed, in the electron energy range up to 20 eV, due to Coster-Kronig electrons from the autoionizing Rydberg states emitted from 2 MeV u-1 Si5+ ions excited through a carbon foil. To obtain a better understanding of these low-energy electron spectra and their production mechanisms, we synthesize the expected electron spectrum which is compared with the observed electron spectrum. Two theoretical methods, namely the perturbation theory of Z-expansion (MZ code) and the multiconfiguration Hartree-Fock method (Cowan code), are used to calculate the necessary Auger electron energies and emission rates. It has been found that the 1s22pnl-1s22s 2S and 1s22s2pnl-1s22s2 1S decays give the most significant contributions to the observed electron spectrum from threshold up to the 20 eV region. The synthetic electron spectra have also been found to reproduce the observed electron spectra quite nicely when the charge distributions of the projectile Si ions after thin carbon foils are taken into account.

Projectile charge state dependence of binary electron production for 1 MeV u-1 Auq+ (q=12-37) ion impact on He

The absolute cross section for the production of binary encounter electrons has been studied at zero degree for highly charged, clothed ions. Experimental and theoretical results for 1 MeV u-1 Auq+ (q=12-37) colliding with helium are presented. It is found experimentally that as the charge state of the incident ion is increased (1) the binary peak magnitude increases, (2) the electron energy at which the peak occurs decreases, and (3) the peak broadens. Classical trajectory Monte Carlo (CTMC) calculations are found to give good account for the magnitude and the shift to lower electron energy of the peak. The continuum distorted wave-eikonal initial state (CDW-EIS) approximation is shown to yield cross sections which are much smaller in magnitude than the experiments, but to reproduce well the relative magnitudes and shapes of the peaks for these ions. It is noted that the increase in the binary peak magnitude with increasing ionic charge state is in distinction to previous measurements which showed enhancement of the binary peak with decreasing charge state for clothed ions.

Radiative Electron Capture for F8+ and F9+ Ions in Collisions with a He Gas Target

The x rays from the radiative electron capture (REC) to the projectile K-shell were investigated for F8+ and F9+ ions incident on the He target atoms in the projectile energy range from 15 to 40 MeV. The peak energies of the K-REC x-ray spectra were found to decrease linearly with a decrease of the projectile energies as expected and extrapolated to the correct ls binding energies at zero velocity. According to theory the distribution width, ¿REC, of the REC energies should be independent of the binding energy of electrons in the projectile ions. However, it is found that ¿REC for F8+ ions is systematically smaller by 20% than that for F9+ ions. The measured REC cross sections for F9+ ions are slightly larger than twice those for F8+ ions and the total REC cross sections for F8+ and F9+ ions were found to be more than three orders of magnitude smaller than the total electron capture cross sections and the capture cross sections into excited states.

Stripping energy dependence of a B3+(1s2 1S,1s2s 3S) beam metastable fraction

The fraction of metastable ions in the B3+(1s2 1S,1s2s 3S) beam was measured as a function of the stripping energy in the range of 0.85 to 9 MeV. This was done by comparing the electron yield of the two final states formed in the collision of B3+ on hydrogen; the 1s2s2p 4P formed by capture from the metastable 1s2s 3S component of the beam and 1s2p2 2D formed by resonant transfer excitation from the ground-state 1s2 1S component of the beam. The double differential cross sections for 1s2s2p 4P and 1s2p2 2D lines were then calculated. The stripping energy was converted to the ratio of projectile velocity to the K-shell electron velocity, vp/vk, which allows using our findings for other He-like ions. It was found that at vp/vk=0.3 no metastable ions are produced. The maximum of the metastable fraction was observed when the stripping foil-projectile relative velocity was near the K-shell electron velocity. The collisionally produced electrons emitted in the forward direction were detected with the new parace...

X-ray satellite lines from doubly excited states of heavy ions with few electrons produced in ion-atom collisions

Abstract Observation and analyses of the satellite X-ray lines from some doubly excited states of fluorine ions with few electrons in ion-atom collisions are reported. The cross sections for production of these doubly excited states for F6+ and F7+ ions in collisions with He atoms are on the order of 10−20 − 10−21 cm2 at the impact energy of 15 MeV.