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R. Schuch

Publications and source records attributed to R. Schuch.

7 recordsLinked to original sources

Rate coefficients for dielectronic recombination of N-like Ne

Dielectronic recombination (DR) for the process Ne$^{3+}$ + e$^{-}$ $\rightarrow$ Ne$^{2+}$ was investigated in a merged-beams arrangement at the heavy-ion storage ring CRYRING@ESR. The energy-dependent DR rate coefficient, $\alpha(E)$ was measured over the electron-ion collision energy range from 0 to 25 eV. The measurements cover the complete set of DR resonance series associated with $2s\to2p$ core excitations. The primary ion beam is estimated to have consisted of $44\%$ of the ions in the ground state, with the remainder distributed among long-lived metastable levels. In addition to the measurements we carried out quantum mechanical calculations of DR cross sections. The theoretical treatment includes contributions from the ground and excited metastable initial levels, weighted according to the estimated beam composition. From the experimental energy-resolved spectra, we derive a temperature dependent DR plasma recombination rate coefficient $\alpha_\mathrm{exp}(T)$ (PRRC). In the temperature domain where Ne$^{3+}$ is abundant in collisionally ionized plasmas, the present results show a good agreement with the present and with previous theoretical predictions. In the low-temperature regime characteristic for photoionized plasmas, the experimentally derived DR plasma rate coefficient is slightly larger than the published theoretical ones and does not agree within the experimental uncertainties. Parametrized fits of the experimentally derived DR PRRC are presented in order to facilitate an easy inclusion into astrophysical modelling codes.

physics.atom-ph

Testing strong-field QED to second-order in the highly correlated atomic system berylliumlike Pb78+ by electron-ion recombination spectroscopy

A low-energy storage ring with an ultracold electron cooler has been coupled with a heavy-ion accelerator facilitating high-resolution electron-ion collision spectroscopy of the heaviest few-electron ions. In the present work resonant electron-ion recombination of berylliumlike Pb$^{78+}$ ions was measured in the collision-energy range 9.3-16.5eV and a value of 244.937(30) eV is derived for the Pb$^{78+}$($2s^2\;^1S_0 - 2s\,2p\;^3P_1$) excitation energy. This result agrees with the most recent (less accurate) theoretical value of 244.942(52) eV [Malyshev et al., Physical Review A 110, 062824 (2024)], which has been calculated by applying strong-field QED rigorously up to the second order. The present investigation suggests that further technical improvements can potentially increase the experimental accuracy by an order of magnitude.

physics.atom-ph

X-ray emission associated with radiative recombination for Pb$^{82+}$ ions at threshold energies

For bare lead ions, decelerated to the low beam energy of 10 MeV/u, the x-ray emission associated with radiative recombination (RR) at "cold collision" conditions has been studied at the electron cooler of CRYRING@ESR at GSI-Darmstadt. Utilizing dedicated x-ray detection chambers installed at 0° and 180° observation geometry, we observed for the very first time for stored ions the full x-ray emission spectrum associated with RR under electron cooling conditions. Most remarkably, no line distortion effects due to delayed emission are present in the well resolved spectra, spanning over a wide range of x-ray energies (from about 5 to 100 keV) which enable to identify fine-structure resolved Lyman, Balmer as well as Paschen x-ray lines along with the RR transitions into the K-, L and M-shell of the ions. To compare with theory, an elaborate theoretical model has been applied. By considering the relativistic atomic structure of Pb$^{81+}$, this model is based on a sophisticated computation of the initial population distribution via RR for all atomic levels up to Rydberg states with principal quantum number $n=$ 165 in combination with cascade calculations based on time-dependent rate equations. Within the statistical accuracy, the experimental x-ray line emission is in very good agreement with the results of the theoretical model applied. Most notably, this comparison sheds light on the contribution of prompt and delayed X-ray emission (up to 70 ns) to the observed X-ray spectra, originating in particular from Yrast transitions into inner shells.

physics.atom-ph

A new mass value for 7Li

A high-accuracy mass measurement of 7Li was performed with the Smiletrap Penning trap mass spectrometer via a cyclotron frequency comparison of Li3+ and H2+. A new atomic mass value of 7Li has been determined to be 7.016,003,425,6,(45)u with a relative uncertainty of 0.63 ppb. It has uncovered a discrepancy as large as 14 sigma (1.1 micro u) deviation relative to the literature value given in the Atomic-Mass Evaluation AME 2003. The importance of the improved and revised 7Li mass value, for calibration purposes in nuclear-charge radii and atomic mass measurements of the neutron halos 9Li and 11Li, is discussed.

nucl-ex

HITRAP: A facility at GSI for highly charged ions

An overview and status report of the new trapping facility for highly charged ions at the Gesellschaft fuer Schwerionenforschung is presented. The construction of this facility started in 2005 and is expected to be completed in 2008. Once operational, highly charged ions will be loaded from the experimental storage ring ESR into the HITRAP facility, where they are decelerated and cooled. The kinetic energy of the initially fast ions is reduced by more than fourteen orders of magnitude and their thermal energy is cooled to cryogenic temperatures. The cold ions are then delivered to a broad range of atomic physics experiments.

physics.atom-ph

Dielectronic Resonance Method for Measuring Isotope Shifts

Longstanding problems in the comparison of very accurate hyperfine-shift measurements to theory were partly overcome by precise measurements on few-electron highly-charged ions. Still the agreement between theory and experiment is unsatisfactory. In this paper, we present a radically new way of precisely measuring hyperfine shifts, and demonstrate its effectiveness in the case of the hyperfine shift of $4s\_{1/2}$ and $4p\_{1/2}$ in $^{207}\mathrm{Pb}^{53+}$. It is based on the precise detection of dielectronic resonances that occur in electron-ion recombination at very low energy. This allows us to determine the hyperfine constant to around 0.6 meV accuracy which is on the order of 10%.

physics.atom-ph

Experimental N V and Ne VIII low-temperature dielectronic recombination rate coefficients

The dielectronic recombination rate coefficients of N V and Ne VIII ions have been measured at a heavy-ion storage ring. The investigated energy ranges covered all dielectronic recombination resonances attached to 2s -> 2p (Delta n=0) core excitations. The rate coefficients in a plasma are derived and parameterized by using a convenient fit formula. The experimentally derived rate coefficients are compared with theoretical data by Colgan et al. (2004, A&A, 417, 1183) and Nahar & Pradhan (1997, ApJ, 111, 339) as well as with the recommended rate coefficients by Mazzotta et al. (1998, A&A, 133, 403). The data of Colgan et al. and Nahar & Pradhan reproduce the experiment very well over the temperature ranges where N V and Ne VIII are expected to exist in photoionized as well as in collisionally ionized plasmas. In contrast, the recommendation of Mazzotta et al. agrees with the experimental rate coefficient only in the temperature range of collisional ionization. At lower temperatures it deviates from the measured rate coefficient by orders of magnitude. In addition the influence of external electric fields with field strengths up to 1300 V/cm on the dielectronic recombination rate coefficient has been investigated.

astro-ph