D. Protic

Applications of position sensitive germanium detectors for X-ray spectroscopy of highly charged heavy ions

The spectroscopy of atomic transitions in the hard X-ray regime above 15 keV utilizing position-sensitive solid state detectors is discussed. Special emphasis is given to the current detector developments for X-ray spectroscopy of heavy ions at the ESR storage ring where applications for precision spectroscopy as well as for polarization studies are of particular interest. For both cases, the advantages and new possibilities which are opened up by position and energy resolving solid state detectors are illustrated by the presentation of first experiments.

Multi-element readout of structured HPGe-detectors for high-resolution x-ray spectroscopy using CUBE-preamplifiers

Very recently we have shown that CUBE-preamplifiers developed by XGLab s.r.l. can be used for the readout of single elements of thick structured planar HPGe- and Si(Li)-detectors produced by SEMIKON [1]. In this paper we will present the results of a simultaneous multi-element readout of structured detectors using the same preamplifiers for measuring high-energy x-rays (more than 100 keV) with a comparable energy resolution as for the single-element readout. Several high-purity germanium detectors (HPGe-detectors) with different position sensitive structures on one detector contact have been used for the first tests. In addition to that we have modified an existing 16-pixel HPGe-polarimeter from GSI-Darmstadt with the new readout. The detector elements (7 mm × 7 mm each, arranged in a 4 × 4 matrix) are connected to CUBE-preamplifiers used in pulse-reset mode. The technological progress achieved with this detector system resulting in a significant improved energy resolution will contribute a lot to much more precise polarization measurements of x-rays emitted from atom-ion collisions which are part of the physics program of the SPARC collaboration (Stored Particles Atomic Physics Research Collaboration) at GSI and the future FAIR accelerator facility (Facility for Antiproton and Ion Research).

A 2D position sensitive germanium detector for spectroscopy and polarimetry of high-energetic x-rays

We report on a first prototype 2D μ-strip germanium detector, developed at IKP-Julich, and its performance test at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. Beside an accurate determination of the detector response function, the polarization sensitivity has been addressed in this study. For this purpose photon beams at energies of 60 keV and 210 keV have been used.

Polarized tunable monoenergetic x-rays produced by radiative electron capture into the K-shell of Xe54+

Many physical processes such as bremsstrahlung, synchrotron radiaton and radiative recombination produce polarized X-rays. However, only a few facilities are able to deliver tunable monoenergetic high quality beams of almost completely polarized X-rays to the user. We used radiative electron capture (REC) into the K-shell of bare xenon to produce tunable and highly linearly polarized X-rays in a storage ring environment (Fig. 1) which we confirmed by a dedicated compton polarimeter.

Polarization Measurements of Radiative Electron Capture Transitions in Highly Charged Ions

A dedicated Si(Li) Compton polarimeter combining energy and time resolution with a large detection area of 64×64u2009mm2 and a two dimensional position resolution of 2 mm has been used for the first time to study the polarization of x‐rays emitted via radiative electron capture (REC) into the K and L‐shell of heavy highly charged ions. First data for the collision system 96.6 MeV/u U92+→H2 are presented. The angular distribution of the Compton scattered photons inside the detector indicates that both K‐ and L‐REC processes lead to the emission of strongly linearly polarized light.

Recent Developments for the Investigation of Ground-State Transitions in Heavy One-Electron Ions

Accurate investigations of the structure of one- and few-electron ions in the high-Z regime provide unique possibilities for testing fundamental theories underlaying our present understanding of of the physics of extremely electro-magnetic strong fields. In this review, we concentrate on x-ray spectroscpic investigations of the ground-state transition energies in H-like uranium (heaviest stable element available) by using the intense beams of cooled heavy ions provided by the storage ring ESR at GSI. Such experiments allow for a precise study of the ground-state binding-energies in high-Z H-like ions where relativistic and QED effects are strongest. The most recent experiment is presented where the deceleration capability of the ESR storage ring was exploited for x-ray spectroscopy at the ESR electron cooler. In addition, we discuss the ongoing developments for a new generation of ground-state Lamb shift experiments aiming on a precision of 1 eV or even better. In particular, emphasis will be given to the dedicated crystal spectrometer (FOCAL) in combination with state of the art 2D position-sensitive solid state detectors, allowing for energy and time resolved x-ray imaging.

Recent experimental developments for the Lamb shift investigation in heavy ions

The latest commissioning experiment of a two arm transmission crystal x-ray spectrometer along with high-performance position-sensitive microstrip germanium detectors is presented. The goal of the experiment was to observe with high resolution the Ly-α-transitions of H-like Pb81+produced in collisions with Kr atoms. Due to a photon e.ciency of only 10−8 the position sensitivity as well as the energy and time resolution of segmented solid state Germanium detectors are absolutely essential for experiments using crystal x-ray spectrometers dealing with beams of heavy ions. A detector system with the desired properties has become available through a collaboration with the Forschungszentrum Julich.

Two-dimensional microstrip germanium detector for X-ray spectroscopy of highly charged heavy ions

New possibilities are opened utilizing position-sensitive germanium detectors in the X-ray spectroscopy of highly charged heavy ions at GSI-Darmstadt. The recent experiments revealed the need for two-dimensional strip detectors with their inherent advantages concerning spectroscopy and imaging capabilities as well as polarization sensitivity. For the first prototype a germanium diode (70 mm /spl times/ 41 mm, 11 mm thick) with a boron implanted contact and an amorphous Ge contact was prepared. A 128 strip structure on an area of 32 mm /spl times/ 56 mm with a pitch of 250 /spl mu/m on the front contact (implanted) and 48 strip structure with a pitch of 1167 /spl mu/m on the rear contact (amorphous Ge) are realized with the help of plasma etching. The detector is mounted in a cryostat which will enable any orientation of the detector in respect to a photon source. The results of laboratory tests and first applications at the ESR storage ring in Darmstadt are presented.

Experimental Developments for the Lamb Shift Investigation in Heavy Ions (abstract)

Novel high‐resolution spectrometer setups are presently commissioned for X‐ray experiments at the Experimental Storage Ring (ESR) at GSI, Darmstadt, aiming at an accurate determination of QED corrections in the critical field limit via an accurate determination of the ground‐state binding energy in a high‐Z, H‐like ion. Until now for H‐like uranium, an accuracy of 1% could be reached in an experiment performed at the electron cooler, due to the deceleration capability of the ESR. A further improvement by almost one order of magnitude is envisaged by a transmission x‐ray spectrometer setup in the FOcusing Compensated Asymmetric Laue (FOCAL) geometry, as well as by the implementation of high‐resolution microcalorimeter devices.Here we report on the latest commissioning experiment of a two‐arm transmission X‐ray spectrometer, along with high‐performance position‐sensitive microstrip germanium detectors. Due to a photon efficiency of only 10−8, the position sensitivity, as well as the energy and time resoluti...

X-ray spectroscopy of highly charged ions: application of position sensitive germanium detectors

Segmented and position sensitive germanium detector systems play an important role for future X-ray spectroscopy experiments with highly charged heavy ions. The unique properties of such systems are millimeter to sub-millimeter spatial resolution as well as a good time and energy resolution for the hard X-ray regime above 15 keV. When dealing with fast moving heavy ions at accelerators or storage rings, this spatial resolution guarantees for a suppression of Doppler broadening without a loss of detection efficiency. Another example is the combination with a focusing crystal spectrometer, where a position-segmented detector permits the measurement of an energy spectrum wide enough to investigate the interesting energy regime simultaneously. In addition, good energy resolution enables discrimination against background events of the recorded spectra arising from various sources. Very recently such a micro-strip detector system, developed at the Forschungszentrum Julich, with a position resolution of close to 200 /spl mu/m has become available An additional important feature of such detector systems is their sensitivity to the photon polarization at energies above 50 keV. By means of such detection devices, the polarization of atomic transitions in highly charged heavy ions can be addressed experimentally with high accuracy.