When logged in, additional information is available in some parts of the website.

Publications by
Dr. Günter Weber

All publications of HI Jena

2019

M. Vockert, G. Weber, H. Bräuning, A. Surzhykov, C. Brandau, S. Fritzsche, S. Geyer, S. Hagmann, S. Hess, C. Kozhuharov, R. Märtin, N. Petridis, R. Hess, S. Trotsenko, Yu. A. Litvinov, J. Glorius, A. Gumberidze, M. Steck, S. Litvinov, T. Gassner, P.-M. Hillenbrand, M. Lestinsky, F. Nolden, M. S. Sanjari, U. Popp, C. Trageser, D. F. A. Winters, U. Spillmann, T. Krings, and Th. Stöhlker
Radiative electron capture as a tunable source of highly linearly polarized x rays
Phyical Review A 99, 052702 (2019)

Abstract: The radiative electron capture (REC) into the K shell of bare Xe ions colliding with a hydrogen gas target has been investigated. In this study, the degree of linear polarization of the K-REC radiation was measured and compared with rigorous relativistic calculations as well as with the previous results recorded for U92+. Owing to the improved detector technology, a significant gain in precision of the present polarization measurement is achieved compared to the previously published results. The obtained data confirms that for medium-Z ions such as Xe, the REC process is a source of highly polarized x rays which can easily be tuned with respect to the degree of linear polarization and the photon energy. We argue, in particular, that for relatively low energies the photons emitted under large angles are almost fully linear polarized.

2018

T. Gassner, M. Trassinelli, R. Heß, U. Spillmann, D. Banas, K.-H. Blumenhagen, F. Bosch, C. Brandau, W. Chen, C. Dimopoulou, E. Förster, R. Grisenti, A. Gumberidze, S. Hagmann, P.-M. Hillenbrand, P. Indelicato, P. Jagodzinski, T. Kämpfer, Ch. Kozhuharov, M. Lestinsky, D. Liesen, Yu. A. Litvinov, R. Loetzsch, B. Manil, R. Märtin, F. Nolden, N. Petridis, M. S. Sanjari, K. Schulze, M. Schwemlein, A. Simionovici, M. Steck, Th. Stöhlker, C. I. Szabo, S. Trotsenko, I. Uschmann, G. Weber, O. Wehrhan, N. Winckler, D. Winters, N. Winters, E. Ziegler, and H. Beyer
Wavelength-dispersive spectroscopy in the hard x-ray regime of a heavy highly-charged ion: the 1s Lamb shift in hydrogen-like gold
New Journal of Physics 20, 073033 (2018)

Abstract: Accurate spectroscopy of highly-charged high-Z ions in a storage ring is demonstrated to be feasible by the use of specially adapted crystal optics. The method has been applied for the measurement of the is Lamb shift in hydrogen-like gold (Au78+) in a storage ring through spectroscopy of the Lyman x-rays. This measurement represents the first result obtained for a high-Z element using high-resolution wavelength-dispersive spectroscopy in the hard x-ray regime, paving the way for sensitivity to higher-order QED effects.

M. Vockert, G. Weber, U. Spillmann, T. Krings, and Th. Stöhlker
Polarization reconstruction algorithm for a Compton polarimeter
Journal of Physics: Conference Series 1024, 012041 (2018)

Abstract: We present the technique of Compton polarimetry using X-ray detectors based on double-sided segmented semiconductor crystals that were developed within the SPARC collaboration. In addition, we discuss the polarization reconstruction algorithm with particular emphasis on systematic deviations between the observed detector response and our model function for the Compton scattering distribution inside the detector.

2017

M. Vockert, G. Weber, U. Spillmann, T. Krings, M. Herdrich, and Th. Stöhlker
Commissioning of a Si(Li) Compton polarimeter with improved energy resolution
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 408, 313 (2017)

Abstract: Abstract On the basis of a double-side segmented Si(Li) crystal a new Compton polarimeter was developed within the SPARC collaboration. The new detector is equipped with a cryogenic first stage of the preamplifiers to improve the energy resolution compared to previous detectors with preamplifiers operating at room temperature. We present first results from a commissioning measurement of the new instrument at the ESR storage ring of GSI in Darmstadt, Germany and contrast it with the performance of an precursor polarimeter system.

M. Herdrich, G. Weber, A. Gumberidze, Z. Wu, and Th. Stöhlker
Fast calculator for X-ray emission due to Radiative Recombination and Radiative Electron Capture in relativistic heavy-ion atom collisions
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 408, 294 (2017)

Abstract: Abstract In experiments with highly charged, fast heavy ions the Radiative Recombination (RR) and Radiative Electron Capture (REC) processes have significant cross sections in an energy range of up to a few GeV / u . They are some of the most important charge changing processes in collisions of heavy ions with atoms and electrons, leading to the emission of a photon along with the formation of the ground and excited atomic states. Hence, for the understanding and planning of experiments, in particular for X-ray spectroscopy studies, at accelerator ring facilities, such as FAIR, it is crucial to have a good knowledge of these cross sections and the associated radiation characteristics. In the frame of this work a fast calculator, named RECAL, for the RR and REC process is presented and its capabilities are demonstrated with the analysis of a recently conducted experiment at the Experimental Storage Ring (ESR) at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Germany. A method is presented to determine unknown X-ray emission cross sections via normalization of the recorded spectra to REC cross sections calculated by RECAL.

2016

M. Drągowski, M. Wlodarczyk, G. Weber, J. Ciborowski, J. Enders, Y. Fritzsche, and A. Poliszczuk
Monte Carlo study of the effective Sherman function for electron polarimetry
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 389, 48 (2016)

Abstract: The PEBSI Monte Carlo simulation was upgraded towards usefulness for electron Mott polarimetry. The description of Mott scattering was improved and polarisation transfer in Moller scattering was included in the code. An improved agreement was achieved between the simulation and available experimental data for a 100 keV polarised electron beam scattering off gold foils of various thicknesses. The dependence of the effective Sherman function on scattering angle and target thickness, as well as the method of finding optimal conditions for Mott polarimetry measurements were analysed.

K.-H. Blumenhagen, S. Fritzsche, T. Gassner, A. Gumberidze, R. Märtin, N. Schell, D. Seipt, U. Spillmann, A. Surzhykov, S. Trotsenko, G. Weber, V. A. Yerokhin, and Th. Stöhlker
Polarization transfer in Rayleigh scattering of hard x-rays
New Journal of Physics 18, 103034 (2016)

Abstract: We report on the first elastic hard x-ray scattering experiment where the linear polarization characteristics of both the incident and the scattered radiation were observed. Rayleigh scattering was investigated in a relativistic regime by using a high- Z target material, namely gold, and a photon energy of 175 keV. Although the incident synchrotron radiation was nearly 100% linearly polarized, at a scattering angle of θ=90° we observed a strong depolarization for the scattered photons with a degree of linear polarization of +27% ± 12% only. This finding agrees with second-order quantum electrodynamics calculations of Rayleigh scattering, when taking into account a small polarization impurity of the incident photon beam which was determined to be close to 98%. The latter value was obtained independently from the elastic scattering by analyzing photons that were Compton-scattered in the target. Moreover, our results indicate that when relying on state-of-the-art theory, Rayleigh scattering could provide a very accurate method to diagnose polarization impurities in a broad region of hard x-ray energies.

M. Lestinsky, V. Andrianov, B. Aurand, V. Bagnoud, D. Bernhardt, H. Beyer, S. Bishop, K. Blaum, A. Bleile, At. Borovik, F. Bosch, C. Bostock, C. Brandau, A. Bräuning-Demian, I. Bray, T. Davinson, B. Ebinger, A. Echler, P. Egelhof, A. Ehresmann, M. Engström, C. Enss, N. Ferreira, D. Fischer, A. Fleischmann, E. Förster, S. Fritzsche, R. Geithner, S. Geyer, J. Glorius, K. Göbel, O. Gorda, J. Goullon, P. Grabitz, R. Grisenti, A. Gumberidze, S. Hagmann, M. Heil, A. Heinz, F. Herfurth, R. Heß, P.-M. Hillenbrand, R. Hubele, P. Indelicato, A. Källberg, O. Kester, O. Kiselev, A. Knie, C. Kozhuharov, S. Kraft-Bermuth, T. Kühl, G. Lane, Y. Litvinov, D. Liesen, X. Ma, R. Märtin, R. Moshammer, A. Müller, S. Namba, P. Neumayer, T. Nilsson, W. Nörtershäuser, G. G. Paulus, N. Petridis, M. Reed, R. Reifarth, P. Reiß, J. Rothhardt, R. Sanchez, M. Sanjari, S. Schippers, H. Schmidt, D. Schneider, P. Scholz, R. Schuch, M. Schulz, V. Shabaev, A. Simonsson, J. Sjöholm, Ö. Skeppstedt, K. Sonnabend, U. Spillmann, K. Stiebing, M. Steck, T. Stöhlker, A. Surzhykov, S. Torilov, E. Träbert, M. Trassinelli, S. Trotsenko, X. Tu, I. Uschmann, P. Walker, G. Weber, D. Winters, P. Woods, H. Zhao, and Y. Zhang
Physics book: CRYRING@ESR
European Physical Journal Special Topics 225, 797 (2016)

Abstract: The exploration of the unique properties of stored and cooled beams of highly-charged ions as provided by heavy-ion storage rings has opened novel and fascinating research opportunities in the realm of atomic and nuclear physics research. Since the late 1980s, pioneering work has been performed at the CRYRING at Stockholm and at the Test Storage Ring (TSR) at Heidelberg. For the heaviest ions in the highest charge-states, a real quantum jump was achieved in the early 1990s by the commissioning of the Experimental Storage Ring (ESR) at GSI Helmholtzzentrum für Schwerionenforschung (GSI) in Darmstadt where challenging experiments on the electron dynamics in the strong field regime as well as nuclear physics studies on exotic nuclei and at the borderline to atomic physics were performed. Meanwhile also at Lanzhou a heavy-ion storage ring has been taken in operation, exploiting the unique research opportunities in particular for medium-heavy ions and exotic nuclei.

P.-M. Hillenbrand, S. Hagmann, J. M. Monti, R. D. Rivarola, K.-H. Blumenhagen, C. Brandau, W. Chen, R. D. DuBois, A. Gumberidze, D. L. Guo, M. Lestinsky, Yu. A. Litvinov, A. Müller, S. Schippers, U. Spillmann, S. Trotsenko, G. Weber, and Th. Stöhlker
Strong asymmetry of the electron-loss-to-continuum cusp of multielectron U²⁸⁺ projectiles in near-relativistic collisions with gaseous targets
Phyical Review A 93, 042709 (2016)

Abstract: The process of electron-loss to the continuum (ELC) has been studied for the collision systems U28+ -> H2 at a collision energy of 50 MeV/u, U28+ -> N2 at 30 MeV/u, and U28+ -> Xe at 50 MeV/u. The energy distributions of cusp electrons emitted at an angle of 0∘ with respect to the projectile beam were measured using a magnetic forward-angle electron spectrometer. For these collision systems far from equilibrium charge state, a significantly asymmetric cusp shape is observed. The experimental results are compared to calculations based on first-order perturbation theory, which predict an almost symmetric cusp shape. Some possible reasons for this discrepancy are discussed.

C. Hahn, G. Weber, R. Märtin, S. Höfer, T. Kämpfer, and Th. Stöhlker
CdTe Timepix detectors for single-photon spectroscopy and linear polarimetry of high-flux hard x-ray radiation
Review of Scientific Instruments 87, 043106 (2016)

Abstract: Single-photon spectroscopy of pulsed, high-intensity sources of hard X-rays — such as laser-generated plasmas — is often hampered by the pileup of several photons absorbed by the unsegmented, large-volume sensors routinely used for the detection of high-energy radiation. Detectors based on the Timepix chip, with a segmentation pitch of 55 μm and the possibility to be equipped with high-Zsensor chips, constitute an attractive alternative to commonly used passive solutions such as image plates. In this report, we present energy calibration and characterization measurements of such devices. The achievable energy resolution is comparable to that of scintillators for γ spectroscopy. Moreover, we also introduce a simple two-detector Compton polarimeter setup with a polarimeter quality of (98 ± 1)%. Finally, a proof-of-principle polarimetry experiment is discussed, where we studied the linear polarization of bremsstrahlung emitted by a laser-driven plasma and found an indication of the X-raypolarization direction depending on the polarization state of the incident laser pulse.

2015

S. Trotsenko, A. Gumberidze, Y. Gao, C. Kozhuharov, S. Fritzsche, H. F. Beyer, S. Hagmann, P.-M. Hillenbrand, N. Petridis, U. Spillmann, A. Surzhykov, D. B. Thorn, G. Weber, and T. Stöhlker
Experimental study of the dielectronic recombination into Li-like uranium
Physica Scripta 2015, 014024 (2015)

Abstract: We have measured the x-rays following 116.15 MeV/u U⁸⁹⁺ collisions with H 2 at 35°, 90°, 120° and 150° observation angles with regard to the ion beam direction. From our experimental spectra combined with radiative electron capture calculations, we obtain angular distribution of characteristic x-rays L to K following the resonance transfer and excitation. Our result shows a good qualitative agreement with theoretical predictions.

K.-H. Blumenhagen, U. Spillmann, T. Gaßner, A. Gumberidze, R. Märtin, N. Schell, S. Trotsenko, G. Weber, and T. Stöhlker
Identification and reduction of unwanted stray radiation using an energy- and position-sensitive Compton polarimeter
Physica Scripta 2015, 014032 (2015)

Abstract: In this work, we report on an experiment that investigated the elastic scattering of linearly polarized 175 keV photons on a gold target. A combined measurement of the angular distribution and the linear polarization of the scattered photons was performed using standard germanium detectors and a double-sided Si(Li) strip polarimeter. Since the data analysis is still in progress, we will show results in forthcoming papers and present here how the polarimeter was used to identify a lack of shielding during the experiment.

D. Hengstler, M. Keller, C. Schötz, J. Geist, M. Krantz, S. Kempf, L. Gastaldo, A. Fleischmann, T. Gassner, G. Weber, R. Märtin, Th. Stöhlker, and C. Enss
Towards FAIR: first measurements of metallic magnetic calorimeters for high-resolution x-ray spectroscopy at GSI
Physica Scripta 2015, 014054 (2015)

Abstract: Metallic magnetic calorimeters are energy dispersive particle detectors that are operated at temperatures below 100 mK. Applied to x-ray spectroscopy they combine the high energy resolution of crystal spectrometers with the large energy bandwidth of semiconductor detectors. After the absorption of a photon its energy is converted into heat. A paramagnetic alloy converts the temperature change into a change of magnetization that is read out by a sensitive superconducting quantum interference device magnetometer. With such a metallic magnetic calorimeter we performed two successful measurements at the internal gas target of the experimental storage ring at GSI. In the first beamtime lithium-like Au-ions were targeted on a N2 and a Xe gas target, respectively. In the second beamtime we observed a projectile beam of bare Xe ions interacting with a Xe gas target. In both experiments we achieved an energy resolution below 60 eV from 0 keV to 60 keV . We were able to detect K-lines of Xe ions of different charge states, including the Lyman series up to Ly-η and could resolve the Ly-β-doublet in H-like Xe.

B. Marx-Glowna, K. Schulze, I. Uschmann, T. Kämpfer, G. Weber, C. Hahn, H.-C. Wille, K. Schlage, R. Röhlsberger, E. Förster, Th. Stöhlker, and G. Paulus
Influence of higher harmonics of the undulator in X-ray polarimetry and crystal monochromator design
Journal of Synchrotron Radiation 22, 1151 (2015)

Abstract: The spectrum of the undulator radiation of beamline P01 at Petra III has been measured after passing a multiple reflection channel-cut polarimeter. Odd and even harmonics up to the 15th order, as well as Compton peaks which were produced by the high harmonics in the spectrum, could been measured. These additional contributions can have a tremendous influence on the performance of the polarimeter and have to be taken into account for further polarimeter designs.

B. Mei, T. Aumann, S. Bishop, K. Blaum, K. Boretzky, F. Bosch, C. Brandau, H. Bräuning, T. Davinson, I. Dillmann, C. Dimopoulou, O. Ershova, Z. Fülöp, H. Geissel, J. Glorius, G. Gyürky, M. Heil, F. Käppeler, A. Kelic-Heil, C. Kozhuharov, C. Langer, T. Le Bleis, Y. Litvinov, G. Lotay, J. Marganiec, G. Münzenberg, F. Nolden, N. Petridis, R. Plag, U. Popp, G. Rastrepina, R. Reifarth, B. Riese, C. Rigollet, C. Scheidenberger, H. Simon, K. Sonnabend, M. Steck, T. Stöhlker, T. Szücs, K. Sümmerer, G. Weber, H. Weick, D. Winters, N. Winters, P. Woods, and Q. Zhong
First measurement of the ⁹⁶Ru(p,γ)⁹⁷Rh cross section for the p process with a storage ring
Physical Review C 92, 035803 (2015)

Abstract: This work presents a direct measurement of the ⁹⁶Ru(p,γ)⁹⁷Rh cross section via a novel technique using a storage ring, which opens opportunities for reaction measurements on unstable nuclei. A proof-of-principle experiment was performed at the storage ring ESR at GSI in Darmstadt, where circulating ⁹⁶Ru ions interacted repeatedly with a hydrogen target. The ⁹⁶Ru(p,γ)⁹⁷Rh cross section between 9 and 11 MeV has been determined using two independent normalization methods. As key ingredients in Hauser-Feshbach calculations, the γ-ray strength function as well as the level density model can be pinned down with the measured (p,γ) cross section. Furthermore, the proton optical potential can be optimized after the uncertainties from the γ-ray strength function and the level density have been removed. As a result, a constrained ⁹⁶Ru(p,γ)⁹⁷Rh reaction rate over a wide temperature range is recommended for p-process network calculations.

G. Weber, H. Bräuning, A. Surzhykov, C. Brandau, S. Fritzsche, S. Geyer, R. E. Grisenti, S. Hagmann, C. Hahn, R. Hess, S. Hess, C. Kozhuharov, M. Kühnel, R. Märtin, N. Petridis, U. Spillmann, S. Trotsenko, D. F. A. Winters, and Th. Stöhlker
Combined linear polarization and angular distribution measurements of x-rays for precise determination of multipole-mixing in characteristic transitions of high- Z systems
Journal of Physics B: Atomic, Molecular and Optical Physics 48, 144031 (2015)

Abstract: By applying novel-type position sensitive x-ray detectors as Compton polarimeters we recently performed a study of the linear polarization of Lyman-α₁ radiation following radiative electron capture into initially bare uranium ions. It was found that a model-independent determination of the ratio of the E1 and M2 transition amplitudes, and consequently of the corresponding transition rates, is feasible by combining the linear polarization data with a measurement of the angular distribution of the emitted radiation. In this work a detailed description of the underlying experimental technique for combined measurements of the linear polarization and the angular distribution of characteristic transitions in high-Z ions is presented. Special emphasis is given to the application of two, two-dimensional position-sensitive x-ray detectors for Compton polarimetry of hard x-rays. Moreover, we demonstrate the polarimeter efficiency of such detector systems can be significantly improved if events, where the charge is spread over neighboring segments, are reconstructed to be used in the polarization analysis.

A. Gumberidze, D. B. Thorn, C. J. Fontes, B. Najjari, H. L. Zhang, A. Surzhykov, A. Voitkiv, S. Fritzsche, D. Banaś, H. Beyer, W. Chen, R. D. DuBois, S. Geyer, R. E. Grisenti, S. Hagmann, M. Hegewald, S. Hess, C. Kozhuharov, R. Märtin, N. Petridis, R. Reuschl, A. Simon, U. Spillmann, M. Trassinelli, S. Trotsenko, G. Weber, D. F. A. Winters, N. Winters, D. Yu, and Th. Stöhlker
Ground-state excitation of heavy highly-charged ions
Journal of Physics B: Atomic, Molecular and Optical Physics 48, 144006 (2015)

Abstract: We have studied the excitation of H-like and He-like uranium (U^91+ and U^90+ ) in relativistic collisions with gaseous targets by observing the subsequent x-ray emission. The experiment was conducted at the ESR storage ring of the GSI accelerator facility in Darmstadt, Germany. The measurements were performed with a newly developed multi-phase target at different collision energies. This enabled us to explore the proton (nucleus) impact excitation as well as the electron impact excitation processes in the relativistic collisions. The large fine-structure splitting in uranium allowed us to unambiguously resolve excitation to different L-shell levels. Moreover, information about the population of different magnetic sublevels has been obtained via an angular differential study of the decay photons associated with the subsequent de-excitation process. The experimental results are compared with calculations performed within the relativistic framework including excitation mechanisms due to both protons (nucleus) and electrons.

H. F. Beyer, T. Gassner, M. Trassinelli, R. Heß, U. Spillmann, D. Banaś, K.-H. Blumenhagen, F. Bosch, C. Brandau, W. Chen, C. Dimopoulou, E. Förster, R. E. Grisenti, A. Gumberidze, S. Hagmann, P.-M. Hillenbrand, P. Indelicato, P. Jagodzinski, T. Kämpfer, C. Kozhuharov, M. Lestinsky, D. Liesen, Y. A. Litvinov, R. Loetzsch, B. Manil, R. Märtin, F. Nolden, N. Petridis, M. S. Sanjari, K. S. Schulze, M. Schwemlein, A. Simionovici, M. Steck, Th. Stöhlker, C. I. Szabo, S. Trotsenko, I. Uschmann, G. Weber, O. Wehrhan, N. Winckler, D. F. A. Winters, N. Winters, and E. Ziegler
Crystal optics for precision x-ray spectroscopy on highly charged ions—conception and proof
Journal of Physics B: Atomic, Molecular and Optical Physics 48, 144010 (2015)

Abstract: The experimental investigation of quantum-electrodydamic contributions to the binding energies of inner shells of highly charged heavy ions requires an accurate spectroscopy in the region of hard x-rays suitable at a limited source strength. For this purpose the focusing compensated asymmetric Laue crystal optics has been developed and a twin-spectrometer assembly has been built and commissioned at the experimental storage ring of the GSI Helmholtzzentrum Darmstadt. We characterize the crystal optics and demonstrate the usefulness of the instrumentation for accurate spectroscopy of both stationary and fast moving x-ray sources. The experimental procedures discussed here may also be applied for other spectroscopic studies where a transition from conventional germanium x-ray detectors to crystal spectrometers seems too demanding because of low source intensity.

G. Weber, H. Ding, M. O. Herdrich, and A. Surzhykov
Towards a fast calculator for the radiation characteristics of radiative recombination and radiative electron capture
Journal of Physics: Conference Series 599, 012040 (2015)

Abstract: The radiative capture of free electrons (radiative recombination) and bound electrons (radiative electron capture) are among the most important charge changing processes for fast, highly-charged ions. While total cross sections can be obtained by an approximate formula with reasonable accuracy, the estimation of angular distributions and polarization properties of the emitted radiation requires a fully relativistic treatment that is numerical expensive. Therefore we recently started the development of a fast calculator for these radiation characteristics. The program is based on a grid of rigorously calculated data points for free- electron capture into bare ions, between which interpolation is performed to obtain radiation characteristics for specific collision systems. Also capture into few-electron systems is taken into account in an approximate way. We present first results from this development.

G. Weber, M. Herdrich, R. DuBois, P.-M. Hillenbrand, H. Beyer, L. Bozyk, T. Gassner, R. Grisenti, S. Hagmann, Y. Litvinov, F. Nolden, N. Petridis, M. Sanjari, D. Winters, and Th. Stöhlker
Total projectile electron loss cross sections of U²⁸⁺ ions in collisions with gaseous targets ranging from hydrogen to krypton
Physical Review ST - Accelerators and Beams 18, 034403 (2015)

Abstract: Beam lifetimes of stored U^(28+) ions with kinetic energies of 30 and 50  MeV/u, respectively, were measured in the experimental storage ring of the GSI accelerator facility. By using the internal gas target station of the experimental storage ring, it was possible to obtain total projectile electron loss cross sections for collisions with several gaseous targets ranging from hydrogen to krypton from the beam lifetime data. The resulting experimental cross sections are compared to predictions by two theoretical approaches, namely the CTMC method and a combination of the DEPOSIT code and the RICODE program.

T. Krings, U. Spillmann, D. Protić, C. Roß, Th. Stöhlker, G. Weber, L. Bombelli, R. Alberti, and T. Frizzi
Multi-element readout of structured HPGe-detectors for high-resolution x-ray spectroscopy using CUBE-preamplifiers
Journal of Instrumentation 10, C02043 (2015)

Abstract: 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).

K.-H. Blumenhagen, A. Gumberidze, R. Märtin, N. Schell, U. Spillmann, G. Weber, and Th. Stöhlker
Characterization of a double-sided Si(Li) strip Compton polarimeter
Journal of Physics: Conference Series 583, 012043 (2015)

Abstract: The response of a double-sided segmented Si(Li) detector system has been investigated. The detector has been irradiated with a collimated, highly linearly polarized beam of 53.2 keV photons from the synchrotron radiation source PETRA III at DESY. The detector was mounted on a platform that could be moved with μm precision thus allowing for a defined beam position on the detector surface. In this paper, the effects of the isolation gaps (gap width = 50 μm) between adjacent segments (strips) were studied, in particular with respect to the effect of charge sharing. The fraction of such charge sharing events increases from about 5% (beam hits center of a strip) to over 50% when the beam is focused just on a gap. The fraction of reconstructed Compton scattering events, which is interesting for Compton polarimetry, amounts to about 3% with the beam impinging at a strip center and 2.8% on average. It can therefore be concluded that events related to charge sharing do not critically degrade the performance of the detector as a Compton polarimter.

G. Weber, K.-H. Blumenhagen, H. Bräuning, H. Ding, S. Fritzsche, S. Hess, R. Märtin, U. Spillmann, A. Surzhykov, S. Trotsenko, D. F. A. Winters, V. A. Yerokhin, and T. Stöhlker
Compton polarimetry using double-sided segmented x-ray detectors
Journal of Physics: Conference Series 583, 012041 (2015)

Abstract: Hard x-ray polarimetry of radiation emitted in collisions of heavy ions, electrons or photons with matter provides detailed information on the collision dynamics as well as of the atomic structure in the presence of extreme field strengths. Moreover, it also opens a route for polarization diagnosis of spin-polarized ion and electron beams which, for example, might be useful in future parity non-conservation studies. Owing to recent progress in the development of highly segmented solid-state detectors, a novel type of polarimeter for the hard x-ray regime has become available. Applied as Compton polarimeters, two-dimensional position-sensitive x-ray detectors now allow for precise and efficient measurements of x-ray linear polarization properties. In this report recent polarimetry studies using such detector systems are reviewed.

2013

N. Winters, A. Warczak, J. A. Tanis, T. Gassner, A. Gumberidze, S. Hagmann, P. M. Hillenbrand, C. Kozhuharov, N. Petridis, R. Reuschl, M. Schwemlein, D. Sierpowski, U. Spillmann, R. Strzalka, S. Trotsenko, G. Weber, D. F. A. Winters, Z. Yin, and Th. Stöhlker
A study of radiative double electron capture in bare chromium ions at the ESR
Physica Scripta 2013, 014048 (2013)

Abstract: Radiative double electron capture is a fundamental atomic process which should be observed in collisions of bare ions with atoms, albeit with a much smaller cross-section than single radiative electron capture. A new experiment—to observe this rare process under single-collision conditions—has been performed at the internal gas jet target of the experimental storage ring at GSI in Darmstadt. X-ray spectra associated with single and double charge exchange have been observed in 30 MeV u^(−1) collisions of bare chromium ions (Cr^(24+)) with helium and nitrogen target gases.

V. A. Yerokhin, A. Surzhykov, R. Märtin, S. Tashenov, and G. Weber
Bremsstrahlung of polarized positrons scattered off atoms
Physica Scripta 2013, 014072 (2013)

Abstract: The leading-order positron–atom bremsstrahlung is investigated within the rigorous relativistic approach based on the partial-wave representation of the Dirac wave functions in the external atomic field. Approximating the atomic target by an effective local potential, we calculate the Stokes parameters of the emitted photon for different polarizations of the initial positron. The results for positron–atom bremsstrahlung are compared with analogous data for the electron–atom bremsstrahlung.

U. Spillmann, K. H. Blumenhagen, E. Badura, M. Balzer, H. Bräuning, J. Hoffmann, K. Koch, N. Kurz, R. Märtin, S. Minami, W. Ott, Th. Stöhlker, G. Weber, and M. Weber
Employing digital pulse processing electronics for the readout of a Si(Li)—Compton—polarimeter for the SPARC collaboration
Physica Scripta 2013, 014103 (2013)

Abstract: The future x-ray spectroscopy and polarimetry experiment program of the SPARC collaboration at GSI and FAIR relies strongly on the availability of two-dimensional position-sensitive, energy- and time-dispersive thick semiconductor detector systems, including the appropriate signal processing electronics. To meet these demands, the development of a compact and scalable data acquisition system that has higher rate acceptance compared to commercial VME electronics by employing digital pulse processing electronics was started.

K. H. Blumenhagen, E. Badura, H. Bräuning, J. Hoffmann, K. Koch, N. Kurz, R. Märtin, S. Minami, W. Ott, U. Spillmann, Th. Stöhlker, G. Weber, and M. Weber
Fully digital readout of segmented solid state detectors
Physica Scripta 2013, 014102 (2013)

Abstract: In this work, the digital readout of semiconductor detectors in combination with digital filters was investigated. Both non-segmented high-purity germanium and segmented planar lithium-drifted silicon detectors were used. In each case, photons from a stationary americium ((241)^Am) gamma source were detected. The resulting preamplifier output pulses were digitized at a fixed sampling frequency and stored entirely. Digital filters were applied to the stored waveforms to extract time and energy information. The performance of different digital filters was compared. The optimum energy resolution obtained was comparable with the value resulting from an analogue readout system based on standard nuclear instrumentation module and versatile module Europe bus electronics.

C. Brandau, C. Kozhuharov, A. Müller, D. Bernhardt, D. Banas, F. Bosch, F. J. Currell, C. Dimopoulou, A. Gumberidze, S. Hagmann, P.-M. Hillenbrand, M. Heil, M. Lestinsky, Y. A. Litvinov, R. Märtin, F. Nolden, R. Reuschl, S. Sanjari, S. Schippers, D. Schneider, D. Shubina, H. Simon, U. Spillmann, Z. Stachura, M. Steck, Th. Stöhlker, G. Weber, M. Wiedeking, N. Winckler, and D. F. A. Winters
Probing nuclear properties by resonant atomic collisions between electrons and ions
Physica Scripta 2013, 014050 (2013)

Abstract: The utilization of the resonant atomic electron–ion collision process of dielectronic recombination (DR) as a tool to probe nuclear properties via isotope shifts and hyperfine effects is discussed. Based on DR, this resonance reaction spectroscopy at electron coolers of heavy-ion storage rings denotes a versatile approach to access nuclear parameters such as charge radius, spin, magnetic moment or lifetimes of long-lived excited nuclear states (isomers). The high sensitivity of DR allows for experiments with artificially synthesized rare isotopes and isomers. Recent experimental progress in the preparation of such exotic species at the ESR storage ring in Darmstadt is presented. The DR technique is exemplified for the case of (234)^Pa^(88+) (Z = 91).

R. Märtin, G. Weber, R. Barday, Y. Fritzsche, J. Enders, U. Spillmann, and Th. Stöhlker
Target-thickness effects in electron–atom bremsstrahlung
Physica Scripta 2013, 014070 (2013)

Abstract: We report on a study of target-thickness effects on the degree of the linear polarization as well as on the emission probability of bremsstrahlung arising in the collision of 100 keV electrons with thin gold targets. For this purpose an experiment at the electron source SPIN at the TU Darmstadt as well as Monte Carlo simulations have been performed. The results indicate that for high- Z targets the degree of linear polarization is significantly altered by straggling of the electrons inside the target.

A. Gumberidze, D. Thorn, C. Fontes, B. Najjari, H. Zhang, A. Surzhykov, A. Voitkiv, S. Fritzsche, D. Banaś, H. Beyer, W. Chen, R. DuBois, S. Geyer, R. Grisenti, S. Hagmann, M. Hegewald, S. Hess, C. Kozhuharov, R. Märtin, I. Orban, N. Petridis, R. Reuschl, A. Simon, U. Spillmann, M. Trassinelli, S. Trotsenko, G. Weber, D. Winters, N. Winters, D. Yu, and Th. Stöhlker
Electron- and Proton-Impact Excitation of Hydrogenlike Uranium in Relativistic Collisions
Physical Review Letters 110, 213201 (2013)

Abstract: The K shell excitation of H-like uranium (U91+) in relativistic collisions with different gaseous targets has been studied at the experimental storage ring at GSI Darmstadt. By performing measurements with different targets as well as with different collision energies, we were able to observe for the first time the effect of electron-impact excitation (EIE) process in the heaviest hydrogenlike ion. The large fine-structure splitting in H-like uranium allowed us to unambiguously resolve excitation into different L shell levels. State-of-the-art calculations performed within the relativistic framework which include excitation mechanisms due to both protons (nucleus) and electrons are in good agreement with the experimental findings. Moreover, our experimental data clearly demonstrate the importance of including the generalized Breit interaction in the treatment of the EIE process.

2012

V. Yerokhin, A. Surzhykov, R. Märtin, S. Tashenov, and G. Weber
Comparative study of the electron-atom and positron-atom bremsstrahlung
Phyical Review A 86, 032708 (2012)

Abstract: Fully relativistic treatment of the electron-atom and positron-atom bremsstrahlung is reported. The calculation is based on the partial-wave expansion of the Dirac scattering states in an external atomic field. A comparison of the electron and positron bremsstrahlung is presented for the single and double differential cross sections and the Stokes parameters of the emitted photon. It is demonstrated that the electron-positron symmetry of the bremsstrahlung spectra, which is nearly exact in the nonrelativistic regime, is to a large extent removed by the relativistic effects.

R. Märtin, G. Weber, R. Barday, Y. Fritzsche, U. Spillmann, W. Chen, R. D. DuBois, J. Enders, M. Hegewald, S. Hess, A. Surzhykov, D. B. Thorn, S. Trotsenko, M. Wagner, D. F. A. Winters, V. A. Yerokhin, and Th. Stöhlker
Polarization Transfer of Bremsstrahlung Arising from Spin-Polarized Electrons
Physical Review Letters 108, 26480 (2012)

Abstract: We report on a study of the polarization transfer between transversely polarized incident electrons and the emitted x rays for electron-atom bremsstrahlung. By means of Compton polarimetry we performed for the first time an energy-differential measurement of the complete properties of bremsstrahlung emission related to linear polarization, i.e., the degree of linear polarization as well as the orientation of the polarization axis. For the high-energy end of the bremsstrahlung continuum the experimental results for both observables show a high sensitivity on the initial electron spin polarization and prove that the polarization orientation is virtually independent of the photon energy.

G. Weber, H. Bräuning, S. Fritzsche, A. Gumberidze, R. Märtin, R. Reuschl, M. Schwemlein, U. Spillmann, A. Surzhykov, D. F. A. Winters, and Th. Stöhlker
Compton polarimeters for the study of hard X-rays arising from energetic collisions of electrons and ions with matter
AIP Conference Proceedings 1438, 73 (2012)

Abstract: Novel position-sensitive x-ray detectors are presented that, when applied as Compton polarimeters, enable precise and efficient linear polarization studies of hard x-rays up to several 100 keV. We give an analytical formula which yields a rough estimate of the polarimeter efficiencies of such detector systems. Moreover, we briefly summarize a recent linear polarization measurement of the Lyman-α1 radiation in a H-like high-Z system, namely U91+.

G. Weber, R. Märtin, A. Surzhykov, M. Yasuda, V. A. Yerokhin, and Th. Stöhlker
PEBSI – A Monte Carlo simulator for bremsstrahlung arising from electrons colliding with thin solid-state targets
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 279, 155 (2012)

Abstract: We present a Monte Carlo code dedicated to the simulation of bremsstrahlung arising in collisions of polarized electrons with thin target foils. The program consists of an electron transport algorithm taking into account elastic electron-nucleus scattering and inelastic collisions with target electrons as well as a treatment of polarized-electron bremsstrahlung emission. Good agreement is found between the predictions of the electron transport code and data stemming from other simulation programs and experiments. In addition, we present first results from the bremsstrahlung simulation which indicate a significant decrease in the degree of linear polarization of bremsstrahlung even for the thinnest gold targets considered.

V. P. Shevelko, M. S. Litsarev, Th. Stöhlker, H. Tawara, I. Y. Tolstikhina, and G. Weber
Electron Loss and Capture Processes in Collisions of Heavy Many-Electron Ions with Neutral Atoms
in: V. Shevelko and H. Tawara (ed.): Atomic Processes in Basic and Applied Physics (Springer Berlin Heidelberg) (2012)

Abstract: The present status and properties of charge-changing processes—electron capture and electron loss—are considered for heavy many-electron ions colliding with neutral atoms over a wide energy range E = 10 keV/u–100 GeV/u. The role of single- and multiple-electron charge-changing processes is discussed, and a brief description of available computer codes for calculation of the corresponding cross sections is presented. Experimental data for electron-loss and capture cross sections for germanium, xenon, lead, and uranium ions colliding with H, N, Ne, Ar, and Xe targets are given in comparison with numerical calculations applying different theoretical models as well as semiempirical formulae.

2011

A. Gumberidze, Th. Stöhlker, D. Banaś, H. F. Beyer, C. Brandau, H. Bräuning, S. Geyer, S. Hagmann, S. Hess, P. Indelicato, P. Jagodziński, C. Kozhuharov, A. Kumar, D. Liesen, R. Märtin, R. Reuschl, S. Salem, A. Simon, U. Spillmann, M. Trassinelli, S. Trotsenko, G. Weber, and D. F. A. Winters
Precision studies of fundamental atomic structure with heaviest few-electron ions
Hyperfine Interactions 199, 59 (2011)

Abstract: One- and few-electron ions traditionally serve as an important testing ground for fundamental atomic structure theories and for the effects of QED, relativity and electron correlation. In the domain of high nuclear charges, new opportunities open up for precise testing and consolidating of the present understanding of the atomic structure in the regime of extreme electromagnetic fields. In this review, the current progress in experimental investigations of the heaviest H- and He-like systems at GSI Darmstadt is presented together with the planned future developments.

R. Märtin, R. Barday, D. Jakubassa-Amundsen, J. Enders, Y. Poltoratska, U. Spillmann, A. Surzhykov, G. Weber, V. A. Yerokhin, and Th. Stöhlker
Polarization Of The High-Energy End Of The Electron-Nucleus Bremsstrahlung In Electron-Atom Collisions
AIP Conference Proceedings 1336, 94 (2011)

Abstract: The linear polarization of bremsstrahlung radiation emitted in collisions of spin‐polarized and unpolarized electrons with carbon and gold targets has been measured for an incident kinetic energy of 100 keV. We present preliminary results for the degree of linear polarization for incident unpolarized electrons as a function of bremsstrahlung photon energy.

Th. Stöhlker, H. F. Beyer, A. Bräuning-Demian, C. Brandau, A. Gumberidze, R. E. Grisenti, S. Hagmann, F. Herfurth, Ch. Kozhuharov, Th. Kühl, D. Liesen, Yu. Litvinov, R. Märtin, W. Nörtershäuser, O. Kester, N. Petridis, W. Quint, U. Schramm, R. Schuch, U. Spillmann, S. Trotsenko, and G. Weber
SPARC: The Stored Particle Atomic Research Collaboration At FAIR
AIP Conference Proceedings 1336, 132 (2011)

Abstract: 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.

V. P. Shevelko, I. L. Beigman, M. S. Litsarev, H. Tawara, I. Yu. Tolstikhina, and G. Weber
Charge-changing processes in collisions of heavy many-electron ions with neutral atoms
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 269, 1455 (2011)

Abstract: Some features of charge-changing processes, namely, electron capture (EC) and electron loss (EL), are considered for heavy many-electron ions colliding with neutral atoms in a wide range of ion energy E = 10 keV/u – 100 GeV/u. The discussion is based on cross-section calculations performed by available computer codes, namely, CAPTURE, DEPOSIT and RICODE. The RICODE (Relativistic Ionization CODE), which provides calculation of single-electron loss cross sections in the relativistic energy regime, was recently created on the basis of the relativistic Born approximation and is described in the Appendix A. In addition, a semi-empirical formula for single-electron loss cross sections is suggested based on properties of the Born approximation and numerical calculations by the RICODE program. To cover also the low and intermediate collision energies, EL cross sections are obtained by the recently created DEPOSIT code which provides calculation of single- and multiple-electron as well as the total cross sections. Based on the results obtained by these codes, recommended capture and loss cross sections for heavy ions like xenon, uranium and lead ions colliding with neutral atoms are presented over a wide energy range.

M. Trassinelli, A. Kumar, H. F. Beyer, P. Indelicato, R. Märtin, R. Reuschl, Y. S. Kozhedub, C. Brandau, H. Bräuning, S. Geyer, A. Gumberidze, S. Hess, P. Jagodzinski, C. Kozhuharov, D. Liesen, U. Spillmann, S. Trotsenko, G. Weber, D. F. A. Winters, and Th. Stöhlker
Differential energy measurement between He- and Li-like uranium intra-shell transitions
Physica Scripta T144, 014003 (2011)

Abstract: We present the first clear identification and highly accurate measurement of the intra-shell transition 1s2p^3P_2 → 1s2s^3S_1 of He-like uranium performed via x-ray spectroscopy. The present experiment was conducted at the gas-jet target of the ESR storage ring in GSI (Darmstadt, Germany), where a Bragg spectrometer, with a bent germanium crystal, and a Ge(i) detector were mounted. Using the ESR deceleration capabilities, we performed a differential measurement between the 1s2p^3P_2→1s2s^3S_1 He-like U transition energy, at 4510 eV, and the 1s^2 2p^2P_(3/2) → 1s^2 2s^2S_(1/2) Li-like U transition energy, at 4460 eV. By a proper choice of the ion velocities, the x-ray energies from the He- and Li-like ions could be measured, in the laboratory frame, at the same photon energy. This allowed for a drastic reduction of experimental systematic uncertainties, principally due to the Doppler effect, and for a comparison with theory without the uncertainties arising from one-photon quantum electrodynamics predictions and nuclear size corrections.

G. Weber, H. Bräuning, R. Märtin, U. Spillmann, and Th. Stöhlker
Monte Carlo simulations for the characterization of position-sensitive x-ray detectors dedicated to Compton polarimetry
Physica Scripta T144, 014034 (2011)

Abstract: We present here a Monte Carlo program based on the EGS5 package for modeling the detector response of position-sensitive x-ray detectors. The program is used to estimate the polarimeter quality of two novel detector systems applied in Compton polarimetry. The validity of the underlying physical models is verified by comparing the simulation output to experimental data obtained at the experimental storage ring, ESR.

D. B. Thorn, A. Gumberidze, S. Trotsenko, D. Banas, H. Beyer, C. J. Bostock, I. Bray, W. Chen, R. DuBois, C. J. Fontes, S. Fritzsche, D. V. Fursa, R. Grisenti, S. Geyer, S. Hagmann, S. Hess, M. Hegewald, C. Kozhuharov, R. Märtin, I. Orban, N. Petridis, R. Reuschl, A. Simon, U. Spillmann, A. Surzhykov, M. Trassinelli, G. Weber, D. F. A. Winters, N. Winters, H. L. Zhang, and Th. Stöhlker
Polarization and anisotropic emission of K-shell radiation from heavy few electron ions
Canadian Journal of Physics 89, 513 (2011)

Abstract: The population of magnetic sublevels in hydrogen-like uranium ions has been investigated in relativistic ion–atom collisions by observing the subsequent X-ray emission. Using the gas target at the experimental storage ring facility we observed the angular emission of Lyman-α radiation from hydrogen-like uranium ions. The alignment parameter for three different interaction energies was measured and found to agree well with theory. In addition, the use of different gas targets allowed for the electron-impact excitation process to be observed.

A. Kumar, S. Trotsenko, A. V. Volotka, D. Banas, H. F. Beyer, H. Bräuning, S. Fritzsche, A. Gumberidze, S. Hagmann, S. Hess, C. Kozhuharov, R. Reuschl, U. Spillmann, M. Trassinelli, G. Weber, and Th. Stöhlker
Spectral distribution of the 2S → 1S two-photon transition in atoms and few-electron ions
Pramana - Journal of Physics 76, 331 (2011)

Abstract: The two-photon decay of the 2S state to the ground state in dressed atoms and one- or two-electron ions has been studied for several decades. Relativistic calculations have shown an Z-dependence of the spectral shape of this two-photon transition in one- or two-electron ions. We have measured the spectral distribution of the 1s2s 1^S_0 → 1s2 1^S_0 two-photon transition in He-like tin at the ESR storage ring using a new approach for such experiments. In this method, relativistic collisions of initially Li-like projectiles with a gaseous target were used to populate exclusively the first excited state, 1s2s, of He-like tin, which provided a clean two-photon spectrum. The measured two-photon spectral distribution was compared with fully relativistic calculations. The obtained results show very good agreement with the calculations for He-like tin.

2010

G. Weber, H. Bräuning, A. Surzhykov, C. Brandau, S. Fritzsche, S. Geyer, S. Hagmann, S. Hess, C. Kozhuharov, R. Märtin, N. Petridis, R. Reuschl, U. Spillmann, S. Trotsenko, D. F. A. Winters, and Th. Stöhlker
Direct Determination of the Magnetic Quadrupole Contribution to the Lyman-alpha(1) Transition in a Hydrogenlike Ion
Physical Review Letters 105, 243002 (2010)

Abstract: We report the observation of an interference between the electric dipole (E1) and the magnetic quadrupole (M2) amplitudes for the linear polarization of the Ly-alpha(1) (2p(3/2) -> 1s(1/2)) radiation of hydrogenlike uranium. This multipole mixing arises from the coupling of the ion to different multipole components of the radiation field. Our observation indicates a significant depolarization of the Ly-alpha(1) radiation due to the E1-M2 amplitude mixing. It proves that a combined measurement of the linear polarization and of the angular distribution enables a very precise determination of the ratio of the E1 and the M2 transition amplitudes and the corresponding transition rates without any assumptions concerning the population mechanism for the 2p(3/2) state.

V. P. Shevelko, Th. Stöhlker, H. Tawara, I. Yu. Tolstikhina, and G. Weber
Electron capture in intermediate-to-fast heavy ion collisions with neutral atoms
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 268, 2611 (2010)

Abstract: Electron capture processes of heavy ions, like Ge(q+), Xe(q+). Pb(q+), and U(q+), respectively, with the charge q approximate to 10-40, occurring in collisions with gaseous targets are considered in the E = 0.1-100 MeV/u projectile energy range. Calculations of single-electron capture cross sections are performed using the CDW and the CAPTURE computer codes These are compared with available experimental data and CTMC (Classical-Trajectory Monte Carlo) calculations. Although the overall agreement is found to be within a factor of two, In some cases of heavy many-electron projectiles, e g. U(28+) + N(2), Ar collisions, experimental cross sections at high energies are far smaller than theoretical predictions Moreover, for these collision systems the observed energy dependencies are quite different from each other. Possible reasons for this behavior and how the theoretical models can be improved are discussed.

G. Weber, H. Bräuning, S. Hess, R. Märtin, U. Spillmann, and Th. Stöhlker
Performance of a position sensitive Si(Li) x-ray detector dedicated to Compton polarimetry of stored and trapped highly-charged ions
Journal of Instrumentation 5, C07010 (2010)

Abstract: We report on a novel two-dimensional position sensitive Si(Li) detector dedicated to Compton polarimetry of x-ray radiation arising from highly-charged ions. The performance of the detector system was evaluated in ion-atom collision experiments at the ESR storage ringe at GSI, Darmstadt. Based on the data obtained, the polarimeter efficiency is estimated in this work.

Q. Zhong, T. Aumann, S. Bishop, K. Blaum, K. Boretzky, F. Bosch, H. Bräuning, C. Brandau, T. Davinson, I. Dillmann, O. Ershova, H. Geissel, G. Gyürky, M. Heil, F. Käppeler, A. Kelić, C. Kozhuharov, C. Langer, T. L. Bleis, Y. A. Litvinov, G. Lotay, J. Marganiec, N. Petridis, R. Plag, U. Popp, R. Reifarth, B. Riese, C. Rigollet, C. Scheidenberger, H. Simon, Th. Stöhlker, T. Szücs, G. Weber, H. Weick, D. F. A. Winters, N. Winters, and P. J. Woods
96^Ru(p,γ)97^Rh measurement at the GSI storage ring
Journal of Physics: Conference Series 202, 012011 (2010)

Abstract: A pioneering experiment was recently performed at the Experimental Storage Ring (ESR) at GSI. Fully stripped ions of 96 Ru were injected into the storage ring and slowed down to a few MeV per nucleon. The 97 Rh ions from the 96 Ru(p,γ) reaction at a newly developed hydrogen jet target were detected with Double Sided Silicon Strip Detectors (DSSSD) mounted inside a pocket. The experiment and the status of the analysis at a beam energy of 11 MeV per nucleon will be presented.

S. Trotsenko, A. Kumar, A. V. Volotka, D. Banas, H. F. Beyer, H. Bräuning, S. Fritzsche, A. Gumberidze, S. Hagmann, S. Hess, P. Jagodzinski, C. Kozhuharov, R. Reuschl, S. Salem, A. Simon, U. Spillmann, M. Trassinelli, L. C. Tribedi, G. Weber, D. Winters, and Th. Stöhlker
Spectral Shape of the Two-Photon Decay of the 2 1S0 State in He-Like Tin
Physical Review Letters 104, 033001 (2010)

Abstract: The spectral distribution of the 1s2s 1S0→1s2 1S0 two-photon decay of He-like tin was measured using a novel approach at the gas-jet target of the ESR storage ring. Relativistic collisions of Li-like projectiles with low-density gaseous matter have been exploited to selectively populate the desired 1s2s state. Compared to conventional techniques, this approach results in a substantial gain in statistical and systematic accuracy, which allowed us to achieve for the first time a sensitivity to relativistic effects on the two-photon decay spectral shape as well as to discriminate the measured spectrum for Sn from theoretical shapes for different elements along the He-isoelectronic sequence.

2009

S. Hess, H. Bräuning, U. Spillmann, S. Geyer, S. Hagmann, C. Kozhuharov, T. Krings, A. Kumar, R. Märtin, B. E. O'Rourke, R. Reuschl, S. Trotsenko, G. Weber, D. Winters, and Th. Stöhlker
Polarized tunable monoenergetic x-rays produced by radiative electron capture into the K-shell of Xe^(54+)
Journal of Physics: Conference Series 194, 012025 (2009)

Abstract: 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.

M. Trassinelli, A. Kumar, H. F. Beyer, P. Indelicato, R. Märtin, R. Reuschl, Y. S. Kozhedub, C. Brandau, H. Bräuning, S. Geyer, A. Gumberidze, S. Hess, P. Jagodzinski, C. Kozhuharov, D. Liesen, U. Spillmann, S. Trotsenko, G. Weber, D. F. A. Winters, and Th. Stöhlker
Observation of the 2p_(3/2) → 2s_(1/2) intra-shell transition in He-like uranium
Europhysics Letters 87, 63001 (2009)

Abstract: We present the first observation of the 1s 2p^3P_2 → 1s 2s^3S_1 transition in He-like uranium. The experiment was performed at the internal gas-jet target of the ESR storage ring at GSI exploiting a Bragg crystal spectrometer and a germanium solid-state detector. Using the 1s^(2) 2p^2P_(3/2) → 1s^(2) 2s^2S_(1/2) transition in Li-like uranium as reference and the deceleration capabilities of the ESR storage ring, we obtained the first evaluation of the energy of an intra-shell transition for a He-like heavy ion.

G. Weber, C. Omet, R. D. DuBois, O. de Lucio, Th. Stöhlker, C. Brandau, A. Gumberidze, S. Hagmann, S. Hess, C. Kozhuharov, R. Reuschl, P. Spiller, U. Spillmann, M. Steck, M. Thomason, and S. Trotsenko
Beam lifetimes and ionization cross sections of U^(28+)
Physical Review Special Topics - Accelerators and Beams 12, 084201 (2009)

Abstract: Beam lifetimes of stored U^(28+) ions with energies between 10 and 180  MeV/u were measured in the heavy ion synchrotron SIS18 and in the experimental storage ring (ESR) of the GSI accelerator facility. By using the internal gas jet target of the ESR, it was possible to obtain projectile ionization cross sections for collisions with H_2 and N_2 from the lifetime data. The experimental cross sections are compared to theoretical data predicted by the n-body classical-trajectory Monte Carlo (CTMC) method of Olson et al. and to calculations of Shevelko et al. using the LOSS-R code. In addition, both theoretical approaches are probed by using the resulting cross sections as input parameters for the STRAHLSIM code, which models the beam losses and, consequently, the lifetimes in the heavy ion synchrotron SIS18. Both the cross section measurement and the SIS18 lifetime study indicate that the LOSS-R code cross sections are in better agreement with the experimental results than the n-body CTMC calculations.

S. Hess, H. Bräuning, U. Spillmann, C. Brandau, S. Geyer, S. Hagmann, M. Hegewald, C. Kozhuharov, T. Krings, A. Kumar, R. Märtin, D. Protic, B. O'Rourke, R. Reuschl, M. Trassinelli, S. Trotsenko, G. Weber, D. F. A. Winters, and Th. Stóhlker
Polarization studies of radiative electron capture into highly-charged uranium ions
Journal of Physics: Conference Series 163, 012072 (2009)

Abstract: Recent advances in the development of 2D microstrip detectors open up new possibilities for hard x-ray spectroscopy, in particular for polarization studies. These detectors make ideal Compton polarimeters, which enable us to study precisely the polarization of hard x-rays. Here, we present recent results from measurements of Radiative Electron Capture into the K-shell of highly-charged uranium ions. The experiments were performed with a novel 2D Si(Li) Compton polarimeter at the Experimental Storage Ring at GSI. Stored and cooled beams of U^(91+) and U^(92+) ions, with kinetic energies of 43 MeV/u and 96 MeV/u respectively, were crossed with a hydrogen gasjet. The preliminary data analysis shows x-rays from the K-REC process, emitted perpendicularly to the ion beam, to be strongly linearly polarized.

H. Bräuning, S. Hess, S. Geyer, U. Spillmann, Ch. Kozhuharov, Th. Krings, A. Kumar, R. Märtin, D. Protic, R. Reuschl, M. Trassinelli, S. Trotsenko, G. Weber, D. Winters, and Th. Stöhlker
Polarization Measurements of Radiative Electron Capture Transitions in Highly Charged Ions
AIP Conference Proceedings 1099, 117 (2009)

Abstract: A dedicated Si(Li) Compton polarimeter combining energy and time resolution with a large detection area of 64 × 64 mm^2 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 U^(92+) → H_2 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.

Th. Stöhlker, D. Banaś, H. Bräuning, S. Fritzsche, S. Geyer, A. Gumberidze, S. Hagmann, S. Hess, C. Kozhuharov, A. Kumar, R. Märtin, B. E. O’Rourke, R. Reuschl, U. Spillmann, A. Surzhykov, S. Tashenov, S. Trotsenko, G. Weber, and D. F. A. Winters
Polarization and angular correlation studies of X-rays emitted in relativistic ion-atom collisions
The European Physical Journal - Special Topics 169, 5 (2009)

Abstract: Particle and photon polarization phenomena occurring in collisions of relativistic ions with matter have recently attracted particular interest. Investigations of the emitted characteristic x-ray and radiative electron capture radiation has been found to be a versatile tool for probing our present understanding of the dynamics of particles in extreme electromagnetic fields. Owing to the progress in x-ray detector technology, in addition, accurate measurements of the linear polarization for hard x-ray photons as well as the determination of the polarization plane became possible. This new diagnostic tool enables one today to derive information about the polarization of the ion beams from the photon polarization features of the radiative electron capture process.

A. Kumar, S. Trotsenko, A. V. Volotka, D. Banaś, H. F. Beyer, H. Bräuning, A. Gumberidze, S. Hagmann, S. Hess, C. Kozhuharov, R. Reuschl, U. Spillmann, M. Trassinelli, G. Weber, and Th. Stöhlker
Spectral shape of the 2E1 decay from 2s state in He-like tin
The European Physical Journal - Special Topics 169, 19 (2009)

Abstract: The two-photon 2E1 transition from the singlet 2s state of heliumlike tin was measured. An alternative experimental approach was adopted in the present investigation where the two-photon emission results from the decay of the 2s state by selective K-shell ionization of Li-like tin ions in relativistic collisions with a low-Z gaseous target, which allowed for a measurement of the undistorted two-photon spectral shape. The measured 2E1 energy distribution was compared with fully relativistic calculations, which predict a Z dependence of the distribution. The preliminary results indicate the best agreement with the relativistic many body calculations for tin, and thus confirm the sensitivity on Z. Detailed data analysis is still in progress.

2007

R. DuBois, O. d. Lucio, M. Thomason, G. Weber, Th. Stöhlker, K. Beckert, P. Beller, F. Bosch, C. Brandau, A. Gumberidze, S. Hagmann, C. Kozhuharov, F. Nolden, R. Reuschl, J. Rzadkjewicz, P. Spiller, U. Spillmann, M. Steck, and S. Trotsenko
Beam lifetimes for low-charge-state heavy ions in the GSI storage rings
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 261, 230 (2007)

Abstract: Lifetimes for 10 – 50 MeV/u U28+ ions were measured for base vacuum conditions in the ESR storage ring at GSI-Darmstadt. The lifetimes are due to total electron loss from U28+ resulting from interactions with background gases in the ring. Lifetimes were also measured for interactions with H2 and N2 targets. These data provide information about the relative magnitudes and energy dependences of the stripping cross-sections resulting from interactions with H2 and N2, gases which represent the primary constituents in high and ultra-high vacuum environments.

S. Trotsenko, T. Stöhlker, D. Banas, C. Z. Dong, S. Fritzsche, A. Gumberidze, S. Hagmann, S. Hess, P. Indelicato, C. Kozhuharov, M. Nofal, R. Reuschl, J. Rzadkiewicz, U. Spillmann, A. Surzhykov, M. Trassinelli, and G. Weber
Investigation of the Decay Properties of the 1s(2s) 2 State in Li-Like Uranium
Journal of Physics: Conference Series 58, 141 (2007)

Abstract: We report on an experiment aiming for a study of the radiative decay modes of the 1s (2s)2 level in Li-like uranium. The experiment was performed of initially Be-like uranium colliding with N2 molecules at an energy of 90 MeV/u. By measuring the x-ray production associated with K-shell ionization of the projectile, a high selectivity for the production of the 1s (2s)2 level is observed.

G. Weber, T. Stöhlker, D. Banas, S. Fritzsche, A. Gumberidze, S. Hagmann, S. Hess, C. Kozhuharov, M. Nofal, U. Popp, R. Reuschl, U. Spillmann, A. Surzhykov, and S. Trotsenko
Radiative processes studied for bare uranium ions in collisions with H_2
Journal of Physics: Conference Series 58, 243 (2007)

Abstract: Radiative processes occurring in collision of decelerated bare uranium ions and molecular hydrogen are studied at the heavy-ion storage ring ESR. The combination of the deceleration technique and the narrow Compton profile of molecular hydrogen allowed us to resolve a multitude of REC transitions into the bound states of the projectile and to resolve unambiguously the tip region of primary bremsstahlung. For this purpose, a supersonic molecular hydrogen jet-target, precooled with liquid nitrogen and optimized for long-term stability, was applied.

R. Reuschl, D. Banas, H. F. Beyer, S. Chatterjee, A. Gumberidze, S. Hess, T. Krings, D. Liesen, D. Protić, U. Spillmann, T. Stöhlker, M. Trassinelli, S. Trotsenko, and G. Weber
Recent experimental developments for the Lamb shift investigation in heavy ions
Journal of Physics: Conference Series 58, 407 (2007)

Abstract: 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 Pb 81+ produced in collisions with Kr atoms. Due to a photon efficiency 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 Jülich.