H. Schmidt-Böcking

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%.

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.

Trajectory, binding and relativistic effects in the K-shell ionization process investigated by particle-photon coincidences

Abstract The influence of the projectile trajectory on the K-shell ionization probability has been investigated by proton and deuteron impact on Ni and Ag by using particle-photon coincidence techniques. Good agreement with calculations in first order peturbation theory is obtained also at very large scattering angles, where higher multipole transitions and the recoil effect have an important influence on the ionization probability. The importance of the increased K-electron binding energy due to the influence of the projectile nuclear charge is demonstrated in the Ne on Ni and Cl on Pb collision systems. Even in the Cl on Pb collision system good agreement is obtained between the first order peturbation theory and experiment, if relativistic united-atom wave functions are used for the 1s electrons.

The determination of the differential energy loss of heavy ions backscattered from an infinitely thick solid target

Abstract A method is described to determine the differential energy loss of heavy ions from the spectrum of heavy ions elastically scattered from an infinitely thick target. Data over a fairly wide energy range can be obtained from a single measurement by a recursive and iterative calculation. The data obtained in this way for 16 O ions in Ni and Au targets are compared to those from other measurements. They differ by less than 5% over the whole energy range investigated (7–35 MeV). The same method also allows the calculation of the elastic or inelastic cross section from known energy loss applying the recurrence formula inversely.

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.

Electronic Sputtering and Desorption Effects in TOF-SIMS Studies Using Slow Highly Charged Ions like Au69+

Secondary ion yields from highly oriented pyrolytic graphite (HOPG) and SiO{sub 2} (native oxide on float zone silicon) targets at impact of slow (v {approx} 0.3 v{sub bohr}) highly charged ions have been measured by Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). A direct comparison of collisional and electronic effects in secondary ion production using a beam of charge state equilibrated 300 keV Xe{sup 1+} shows a secondary ion yield increase with incident ion charge of {>=}100.

Interference effects in K vacancy transfer of hydrogenlike S ions colliding with Ar

The impact-parameter-dependent K-shell to K-shell vacancy transfer probability has been investigated for 4.7, 7.9, 16, 32 and 90 MeV S15+-Ar collisions by measuring S and Ar K X-ray particle coincidences. With low-energy H-like S beams (obtained by poststripping S at 108 MeV and decelerating with the Heidelberg RF linac), oscillating Ar K vacancy probabilities as a function of impact parameter were measured. This structure can be interpreted as constructive and destructive interference of the transfer amplitudes on incoming and outgoing parts of the trajectory. Thus measurement of the height as well as the phase of the coupling amplitude allows for a very sensitive test of different coupling models. The interference maxima and minima could be related to values of the phase integral over the 2 p sigma -1 s sigma energy difference from which information about this energy difference could be obtained.

Experimental Determination of the Production Mechanism for Noncharacteristic Radiation in Swift Heavy-Ion Collisions*

Absolute differential cross sections of non-characteristic radiation emitted in energetic heavy-ion collisions (EP=3.92–48 MeV,Z=11–22) can only be explained in the framework of quasimolecular radiation. All other processes, particularly bremsstrahlung mechanisms are found to be negligible. For high projectile and photon energies the one-step quasimolecular radiation is dominant in solid targets, whereas the two-step process contributes mainly at low projectile and photon energies.