C. Biedermann

Properties of cold ions produced by synchrotron radiation and by charged particle impact

Argon recoil ions produced by beams of 0.8 MeV/u Cl/sup 5 +/ have been detected by time-of-flight (TOF) techniques in coincidence with the loss of from one to five projectile electrons. Recoil-ion energies have been determined to be more than an order of magnitude higher than those of highly-charged ions produced by unmonochromatized synchrotron radiation. Charge-state distributions, however, show similarities, suggesting that loss of projectile electrons corresponds, in some cases, to inner-shell target ionization producing vacancy cascades. In an essential improvement to the usual multinomial description of ionization in the independent-electron-ejection model, we find the inclusion of Auger vacancy cascades significantly alters the description of the recoil ion spectra corresponding to projectile-electron loss. These conclusions are consistent with impact parameters inferred from determinations of mean recoil energy. 11 refs., 5 figs.

Production of highly-charged recoil-ion beams at very low energy

Abstract An apparatus for production of an intense, charge-state separated, recoil-ion beam of very low energy and good collimation has been constructed. In a test experiment, in which 30 MeV C15+ projectiles were used to produce recoil ions, the feasibility of the method was demonstrated. The mass to charge ratio of the beam is selected by means of a Wien-filter, and the beam energy can be varied between 2qeV and 1q keV with a constant charge-state resolution. Presently, the angular definition of the beam is 2.5°, but it can be impoved by at least a factor of 2. Very low energy Ar-ion beams, of intensities usable for secondary slow collision experiments, can be created for charge states ranging from one to nine. For example, beams of Ar4+ and Ar6+ of intensities 2.5 × 104 and 5 × 103 s−1, respectively, can be furnished at energies of 10 q eV, while the corresponding numbers for 2 q eV beams ar approximately five times lower.

Angular distributions for single- and double-electron capture in slow C4+-Ne collisions.

In an earlier experiment by H. Cederquist [ital et] [ital al]. [J. Phys. B 18, 3951 (1985)] an unusual [ital Q]-value distribution for true double-electron capture was reported for 400-eV C[sup 4+]-Ne collisions: a strong population of reaction channels resulting in [ital Q] values between 27 and 35 eV followed by weakly populated channels in the region 18--25 eV and then again a strong channel at [ital Q]=16 eV. The last channel is nearly degenerate in [ital Q] value with the dominant single-electron capture reaction. Here, we report measured angular distributions for scattered projectiles in single- and double-electron capture at collision energies 0.6--1.0 keV. At 0.6 keV, both single- and double-electron capture exhibit strong forward peaks for [ital Q][similar to]16 eV. The intensity for the latter, but not the former, decreases drastically when the energy is raised to 1 keV. The energy dependence of the angular distribution for double-electron capture with [ital Q][gt]20 eV can be qualitatively understood in simple terms; single-electron captures to 2[ital s] and 2[ital p] orbitals, however, yield unexpectedly wide and structured angular distributions.

Production and transport of convoy electrons in amorphous carbon foils

Abstract The production of free convoy electrons, emitted with velocities near the ion velocity in ion-solid collisions, is not well understood. Experiments concerning thickness-dependent yields have suggested the dominant mechanism for convoy production is electron loss to the continuum (ELC) in the bulk of the solid. Free electrons created in the bulk are subject to multiple elastic and inelastic scattering during transport through remaining layers of the solid. We discuss double-differential measurements of convoy electrons as a function of target thickness for fast O 5+ ion projectiles incident on carbon foils of varied thicknesses. Angular distributions confirm the ELC model for convoy production. From the radial broadening of the convoy cusps we have determined energy and angular spreading parameters due to postcollisional multiple scattering.