Resonant recombination at ion storage rings: a conceptual alternative for isotope shift and hyperfine studies

Abstract

Sharp resonant structures in the cross section of the atomic electron-ion collision process of dielectronic recombination are exploited to study isotope shifts and hyperfine interaction of heavy highly-charged ions. This novel approach provides a conceptual alternative to existing methods. In this contribution, we present a series of measurements, which we performed at the heavy ion storage ring ESR of the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany. In a first experiment the stable isotopes A = 142 and A = 150 of three-electron neodymium ^ANd^57 + were studied. Isotope shifts of dielectronic resonances associated with 2s − 2p _j (j = 1/2, 3/2) transitions were extracted from the measured data. The evaluation of the energy shift was performed within a full QED framework and yielded a change in the mean-square charge radius of $^{142,150}\delta \langle r^2 \rangle = -1.36(1)(3)$ fm². At GSI, in addition to the investigation of stable isotopes unstable species can be artificially synthesized and studied. Radioisotopes produced in-flight from fragmentation of a ²³⁸U primary beam were injected into the ESR and were subsequently separated by their mass-to-charge ratio. This enabled us to perform first DR experiments with the exotic nuclei ²³⁷U^89 + (Z = 92 )and ²³⁴Pa^88 + (Z = 91).