Subshell-selective x-ray studies of radiative recombination ofU92+ions with electrons for very low relative energies

Abstract

Radiative recombination (RR) into the K shell and L subshells of U 92+ ions interacting with cooling electrons has been studied in an x-ray RR experiment at the electron cooler of the Experimental Storage Ring at GSI. The measured radiative recombination rate coefficients for electron-ion relative energies in the range 0-1000 meV demonstrate the importance of relativistic effects. The observed asymmetry of the measured K-RR x-ray emission with respect to the cooling energy, i.e., zero average relative velocity (v rel = 0), are explained by fully relativistic RR calculations. With our new approach, we show that the study of the angular distribution of RR photons for different relative energies opens new perspectives for detailed understanding of the RR of ions with cooling electrons in cold magnetized plasma.

Physics book: CRYRING@ESR

“…Storage rings for heavy ions provide unique conditions for x-ray spectroscopy of photonic transitions involving the interaction of high-Z few electron ions with particle probes, such as atoms in a gas target or with electron beams (Stöhlker et al, 1995(Stöhlker et al, , 1998Rzadkiewicz et al, 2006;Gumberidze et al, 2010;Reuschl et al, 2008;Eichler and Stöhlker, 2007;Nofal et al, 2007). The high luminosity of storage rings along with very clean, almost background free experimental conditions are a prerequisite for the success of these studies where elementary and fundamental dynamical processes (Stöhlker et al, 1995;Gumberidze et al, 2010;Reuschl et al, 2008;Eichler and Stöhlker, 2007;Nofal et al, 2007;Banaś et al, 2015) as well as the structure properties of high-Z one-and few-electron ions have been addressed in a broad range of experiments by applying various techniques, e.g. angular distribution studies (Stöhlker et al, 1997;Stöhlker et al, 1999Stöhlker et al, , 2001, polarimetry (Tashenov et al, 2006(Tashenov et al, , 2014Weber et al, 2010;Märtin et al, 2012), and precision x-ray spectroscopy (Stöhlker et al, 1993;Beyer et al, 1995;Stöhlker et al, 2000;Gumberidze et al, 2005Gumberidze et al, , 2004Trassinelli et al, 2009;Beyer et al, 2004;Chatterjee et al, 2006;Trotsenko et al, 2010).…”

“…QED effects whose evaluation has been recently completed following very extensive theoretical work (Yerokhin and Shabaev, 2015). A highly desired experimental scenario would be quite similar to the experimental scheme which has been applied very successfully for the study of the 1s-Lamb Shift at the ESR electron cooler (Beyer et al, 1995;Gumberidze et al, 2005) (see also Figure 2.2) except that, besides 0 spectroscopy, photon detection at 180 (Banaś et al, 2015) will be added. Therefore, the new approach includes the combination of 0 and 180 spectroscopy at the electron cooler for strongly decelerated ions at energies close to 10 MeV/u.…”

“…The interaction of HCI beams with atomic or molecular beams (Rzadkiewicz et al, 2006;Gumberidze et al, 2010, Section 2.1.1) or free electrons (Section 2. 1.3 Gumberidze et al, 2005;Banaś et al, 2015) has been successfully studied by means of x-ray spectroscopy in order to investigate fundamental interactions such as, e.g., radiative electron capture and its time-reversed counterpart, i.e., the photoelectric effect, in highly charged systems. In addition, beam-foil spectroscopy in the x-ray regime has proven to be a powerful tool for the measurement of dipole transition rates and corresponding lifetimes of excited states (Toleikis et al, 2004, Section 2.1.4).…”

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

“…Further detailed experimental studies of this process for low-to mid-Z ions in various electronic configurations [3][4][5][6][7] and even manyelectron ions at high-Z [8,9] have been facilitated, in particular, by the advancement of ion storage rings employ-ing electron cooler devices (such as ASTRID, CRYRING, and TSR). For the heaviest ion species these studies were extended at the electron cooler of the ESR ion storage ring [10][11][12][13]. Moreover, at high relative collision energies, complementary studies have been performed at Electron Beam Ion Trap devices (EBIT) [14,15].…”

“…Moreover, recently, even quantum electrodynamics (QED) contributions have been taken into account in the description of the RR process [24,25]. Here, we would like to stress that even though RR has been studied quite intensively over decades and many interesting insights have been gained into various aspects of this process, there are still certain experimental observations which are not yet fully understood [5,7,10,11,13,26].…”