Radiative electron capture into theK-, L- andM-Shell of decelerated, hydrogenic Ge projectiles

Abstract

Abstract. Radiative Electron Capture (REC) in 4 to 12MeV/u Ge31+---~H2 collisions has been studied using an X-ray/particle coincidence technique. This technique allowed a systematic investigation of K-shell REC as well as a separation of REC into the projectile L-and Mshells. The cross sections are discussed within a general scaling picture based on the reduced projecti!e velocity. PACS: 34.70. + e When a highly charged ion interacts with a neutral target atom several recombination processes are possible. Radiative Electron Capture (REC) is a recombination phenomenon in which the highly charged ion captures a target electron and emits a photon. REC of free electrons, considered as a time reversed photoeffect, has been known for a long time [1]. However, it was not until 1972 that REC of bound, quasi-free target electrons was observed [2] and studied intensively, both experimentally and theoretically [3][4][5][6][7][8][9][10][11][12][13][14][15]. Within the impulse approximation quasi-free electrons can be treated as free as long as the binding energy in the target atom can be neglected with respect to the kinetic electron energy seen in the projectile frame. Detailed knowledge of the REC process is important for an understanding of ionic states in solid matter [12,16,17], tbr a description of capture processes in high energy collisions [15"], for modelling of electron cooling processes in storage rings [18], and the estimations of lifetimes of highly charged stored ions. Very recently, the application of REC for structure studies of heavy few-electron ions has been proposed as well [19].In this letter we report on the first systematic case studies for K-, L-, and M-REC observed in collisions of highly charged, decelerated heavy ions (Ge 31 +) with a H2 gas target in the energy range 4.5 to 11.5 MeV/u. It should be noted that the simultaneous detection of all three processes in one collision system is very difficult * Supported by KBN, Poland; Grant No. 201779101 due to background in the X-ray spectra produced by inner-shell excitation or ionization, non-radiative electron capture into projectile excited states, and electron bremsstrahlung. Therefore, in order to reduce the background from competing processes, coincidences between X-Rays and projectiles which captured one electron were registered in our experiment. To date, simultaneous observation of K-, L-, and M-REC was only possible for channeling conditions at energies similar to those used in our experiment [12]. In this case small impact-parameter processes like K-shell excitation and non-radiative capture were strongly reduced.The hydrogenic Ge 3t+ projectiles, at the energies mentioned above, were produced at the UNILAC facility of GSI Darmstadt by stripping in a C foil at 11.5 MeV/u and by subsequent deceleration down to the appropriate energies [20]. The charge state analyzed beam was collimated and directed into the collision area which consisted of an open, triply differentially pumped gas target. The central part of the target of 7.5 mm length was ob...

Relativistic quantum dynamics in strong fields: photon emission from heavy, few-electron ions

“…REC into highly-charged ions has been investigated since a long time as it represents the dominant charge exchange process for bare and H-like ions in collisions with low-Z targets at high energies (Schnopper et al 1972, Spindler et al 1979, Anholt et al 1984, Stöhlker et al 1992, Stöhlker et al 1995, Vane et al 2000. In this radiative recombination (RR) process, a free or quasi-free electron is captured into a bound state of the ion under the simultaneous emission of a photon.…”

Radiative electron capture by relativistic heavy ions

“…The large discrepancy between plane-wave calculations and experiment can be remedied by multiple-scattering corrections, such as the Stöbbe formula (Stöhlker et al 1992). More generally the transition amplitude for the DWIA is given by…”

“…This feature is accompanied by a background of electronic and nuclear bremsstrahlung and, in certain cases, an intense broad structure due to emission from quasimolecular states (Greiner et al 1985). If the target atom is rather light and the projectile is highly charged and very fast (Stöhlker et al 1994(Stöhlker et al , 1995, then it is a suprising fact that electron capture via vacuum coupling is a stronger channel than potential scattering (Eichler 1990;Ichihara et al 1994;Stöhlker et al 1992;Mokler et al 1991;Deco & Rivarola 1989). An important aspect of the collision is that strong spin-orbit coupling gives rise to magnetic (spin-flip) transitions during photoemission.…”

“…An important aspect of the collision is that strong spin-orbit coupling gives rise to magnetic (spin-flip) transitions during photoemission. Although such effects are very important for high-Z collisions at high energies, the non-relativistic dipole approximation (Shakeshaft & Spruce 1979) is in fact remarkably accurate for intermediate-Z and kinetic energies up to 1 GeV u −1 (Stöhlker et al 1992). Experiments have recently been performed to measure the rate of such processes and the frequency and angular distribution of the photoemission.…”

Radiative electron capture as a tunable source of highly linearly polarized x rays

“…Radiative electron capture (REC) is known as the dominant electron-capture process in fast collisions of heavy, highly charged ions with light target atoms and has attracted a lot of attention since its discovery in the early 1970s [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. In this process, the capture of an electron from a target atom into a bound state of a projectile is accompanied by the emission of a photon that carries away the excess energy and momentum.…”