D. Banas

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.

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.

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.

Polarization and anisotropic emission of K-shell radiation from heavy few electron ions

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.

Investigation of the Decay Properties of the 1s(2s)2 State in Li-Like Uranium

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.

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.

Radiative processes studied for bare uranium ions in collisions with H2

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.

Radiative Electron Capture to Continuum (RECC) in 90AMeV U88+(1s22s2) + N2: the Short Wavelength Limit of Electron Nucleus Bremsstrahlung

We have investigated the relation of forward emission cusp electron spectra and bremsstrahlung for 90AMeV U88+ + N2at the internal supersonic gas jet target of the ESR storage ring of GSI. We find that x ray photons measured in coincidence with cusp electrons originate from the short wavelength limit of the electron nucleus bremsstrahlung.

Wavelength-dispersive spectroscopy in the hard x-ray regime of a heavy highly-charged ion: The 1s Lamb shift in hydrogen-like gold

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 1s Lamb shift in hydrogen-like gold (Au 78+) 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.

FOCAL - precision x-ray spectroscopy for extreme fields in high-z ions

H.F. Beyer1, D. Banaś2, K.-H. Blumenhagen8, F. Bosch1, C. Brandau4, W. Chen1, Chr. Dimopoulou1, E. Forster3,8, T. Gasner1,8, A. Gumberidze4, S. Hagmann1,5, R. Hes1, P.-M. Hillenbrand1, P. Indelicato6, P. Jagodzinski2, T. Kampfer8, Chr. Kozhuharov1, M. Lestinsky1, D. Liesen1, Yu.A. Litvinov1, R. Loetzsch8, B. Manil7, R. Martin8, F. Nolden1, N. Petridis4,5, M.S. Sanjari1,4, K.S. Schulze8, M. Schwemlein1, A. Simionovici10, U. Spillmann1, M. Steck1, Th. Stohlker1,8, C.I. Szabo6, M. Trassinelli10, S. Trotsenko8, I. Uschmann3,8, G. Weber8, O. Wehrhan3,8, N. Winckler1, D. Winters1, N. Winters1, and E. Ziegler11 1GSI Helmholtzzentrum, Darmstadt, Germany; 2Institute of Physics, Swietokrzyska Academy, Kielce, Poland; 3Inst. fur Optik und Quantenelektronik, Friedrich-Schiller-Universitat, Jena, Germany; 4Extreme Matter Institute, EMMI, GSI Helmholtzzentrum, Darmstadt, Germany; 5Institut fur Kernphysik, Goethe-Universitat, Frankfurt am Main, Germany; 6Lab. Kastler Brossel, Universite P. et M. Curie, Paris, France; 7Laboratoire de Physique des Lasers (LPL) UMR 7538 CNRS Universite Paris 13, Villetaneuse, France; 8Helmholtz-Institut Jena, Jena, Germany; 9LGIT, Observatoire des Sciences de l’Univers de Grenoble, Grenoble, France; 10Institut des Nanosciences de Paris, Universite Pierre et Marie Curie-Paris 6 and CNRS-UMR 7588, Paris, France; 11ESRF, Grenoble, France Introduction and Motivation The extraordinarily strong electric field provided by the nucleus of a very heavy one-electron ion exposed to its inner electrons is the testing ground for bound-state quantum electrodynamics (QED) in a largely unexplored domain. Experimentally the QED contribution to the 1s binding energy is accessible via a direct measurement of the K-shell transitions with sufficient accuracy. The corresponding Lyman transitions in highZ ions lie in the hard x-ray region. Previously the x-ray energy has been measured with the aid of germanium xray detectors of limited resolution [1]. The present experiment marks the leap to wavelength-dispersive spectroscopy of substantially higher spectral resolving power simultaneously coping with the low x-ray intensity.