R. Schuch

A position sensitive parallel plate avalanche detector for heavy-ion X-ray coincidence measurements

Abstract A position sensitive parallel plate avalanche detector has been developed as particle detector for heavy-ion X-ray coincidence measurements. With 20 MeV Ne ions the detector can handle counting rates of more than 2 × 106 particles/s on an area of 0.1 mm2 and it has a position sensitivity of 0.35 mm. The detector has a ring geometry allowing to detect simultaneously particles over an impact-parameter range bmax ≈ 100bmin solution Δb/b ≈ ±5%.

Experiments with highly-charged ions in the storage ring TSR

Experiments with merged electron and ion beams at the Heidelberg Test Storage Ring (TSR) are described. The experimental conditions of radiative and dielectronic recombination measurements are discussed. Results are presented for the radiative recombination rates of bare C and Cl nuclei, and for the dielectronic recombination of H-like, He-like, and Li-like ions up to charge 26.

Analysis of time-spectra from coincidence measurements with high stop-rates☆

Abstract The development of new types of particle detectors makes possible coincidence measurements of low probabilities with very high particle stop-rates (>MHz). A consequence of a high stop-rate is, however, a loss of true coincidences, which are included in the random background. This effect becomes more severe if the position channels of a position-sensitive particle detector are used to stop a single TAC (time-to-amplitude-converter). An analytical description of time-spectra is developed and tested by a simulated coincidence experiment. A procedure is described, which can be used to determine the contents of the time-peak and to correct for the loss of the true coincidence.

Measurement of the total cross sections for electron capture of 2.0-7.5 MeV H+ in H, H2 and He

The total cross sections for electron capture of protons in atomic and molecular hydrogen and in helium gas targets are measured in the high proton velocity regime of 2.0, 3.5, 5.0 and 7.5 MeV. The results are compared with first- and higher-order perturbation theories (Oppenheimer-Brinkmann-Kramers, true first Born approximation, eikonal approximation, continuum distorted wave, strong potential Born, strong potential Born full peaking) for electron capture and are found to be in good agreement with the CDW, EA and TFBA approximations.

SPARC: The Stored Particle Atomic Research Collaboration At FAIR

The future international accelerator Facility for Antiproton and Ion Research (FAIR) encompasses 4 scientific pillars containing at this time 14 approved technical proposals worked out by more than 2000 scientists from all over the world. They offer a wide range of new and challenging opportunities for atomic physics research in the realm of highly‐charged heavy ions and exotic nuclei. As one of the backbones of the Atomic, Plasma Physics and Applications (APPA) pillar, the Stored Particle Atomic Physics Research Collaboration (SPARC) has organized tasks and activities in various working groups for which we will present a concise survey on their current status.

Systematic study of impact parameter dependent K-vacancy probabilities in near symmetric gas- and solid-target collision systems

K-vacancy production probabilitiesPK(b) were measured with gas and solid targets byK-x-ray particle coincidences (impact parameterb is determined by the particle detection angle) in the region of light (ZP≃ZT≃10) up to intermediate heavy (ZP≃ZT≃36) collision systems. The measuredPK(b) reveal a very strong difference in shape between solid and gas targets independent ofZ. Only thePK(b) measured with gas targets and those measured with solid targets at very small impact parameters show reasonable good agreement with the 2pπx-2pσ rotational coupling model. At largeb thePK(b) from solid targets are strongly influenced by a multiple collision effect, where projectileL-vacancies seem to be produced in collisions beforeK-vacancy production. However, this effect cannot be understood just by a two collision process whereL-vacancy production and 2pπx-2pσ rotational coupling occurs in consecutive collisions.

The quasimolecular 1sσ orbital in collision systemsα(Z1+Z2)≳1, its excitation and spectroscopy

An analytical formula for the excitation probability of the quasimolecular 1sσ orbital as a function of the impact parameterb is derived for collision systems withα(Z1+Z2)≳1. This formula describes well all existing experimental data for those collision systems except for the heaviest system Pb+Cm (Z1+Z2=178) at impact parametersb≲40 fm. It is discussed in which way energies of the quasimolecular 1sσ orbital can be extracted from experimental 1sσ vacancy production data.

The contribution ofK-electron capture for the production of highly charged Ne recoil ions by 156 MeV bromine impact

The recoil ion production cross sections in 2MeV/amu Brn++Ne0→Brn′++Neq+ were measured using a projectile ion — recoil ion coincidence technique where the final charge states of both collisions partners were detected simultaneously. Multiple ionization was found to be the dominant process for the production of low charge state recoil ions whereas the production of highly charged recoil ions is accompanied by electron capture from the Nek-shell. The derived ratio of single to double Ne-k electron capture probabilities indicates deviations from a binomial statistics distribution.

Double electron capture of He2+ from He at high velocity

The double electron capture process by He2+ ions in collisions with helium is studied in the high velocity regime with the measurement of total cross sections at 1.5, 4 and 6 MeV beam energy and angular differential cross sections for 1.5 MeV. The experimental results compare well with theoretical calculations which include correlation effects in the initial and final He ground states for the derivation of the capture amplitude in a continuum distorted-wave approximation.

Atomic physics at the Heidelberg Test Storage Ring (TSR)

Abstract A brief description of the Heavy-Ion Test Storage Ring (TSR) presently being built at the Max-Planck Institut in Heidelberg is given. It will be able to store ions injected from the tandem postaccelerator combination up to ∼ 30 MeV/nucleon for a charge to mass ratio of 0.5. One of the main purposes of the TSR will be the study of electron cooling. Some atomic physics experiments are discussed using the electron cooling device which provides an electron-ion collision facility with good energy resolution and ion beams of high currents and low emittances. Here the possibilities for measurements of spontaneous and laser-induced radiative recombination and dielectronic recombination in the electron cooling section are discussed.