X. Y. Ma

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.

Precision tests of QED in strong fields: experiments on hydrogen- and helium-like uranium

In this contribution, we present an experimental study carried out at GSI Darmstadt devoted to investigation of quantum electrodynamical (QED) effects for the ground states in hydrogen- and helium-like uranium. In the experiment, X-ray spectra following radiative recombination of free electrons with bare and H-like uranium ions (U92+, U91+) were measured at the electron cooler of the ESR storage ring. Utilizing clean and favorable experimental conditions present at the electron cooler, we were able to obtain very accurate values for the ground-state binding energies from the observed X-ray transitions. When compared with theory, our results provide the most stringent test of bound-state QED for one- and two-electron systems in the strong-field regime.

A Progress Report of 320 kV Multi-discipline Research Platform for Highly Charged Ions

A dedicated platform for multi-disciplinary research with highly charged ions has been constructed, and an all-permanent magnet ECR ion source was built and installed in the beamline. Five experimental terminals are established for interdisciplinary Research. The high voltage supplied to the platform has reached 320 kV. The commissioning of the platform is successful, different ion beams have been provided for experimental studies, and the current status will be reported.

Assembly and Installation of the Daya Bay Antineutrino Detectors

The Daya Bay reactor antineutrino experiment is designed to make a precision measurement of the neutrino mixing angle θ_(13), and recently made the definitive discovery of its non-zero value. It utilizes a set of eight, functionally identical antineutrino detectors to measure the reactor flux and spectrum at baselines of ~ 300–2000 m from the Daya Bay and Ling Ao Nuclear Power Plants. The Daya Bay antineutrino detectors were built in an above-ground facility and deployed side-by-side at three underground experimental sites near and far from the nuclear reactors. This configuration allows the experiment to make a precision measurement of reactor antineutrino disappearance over km-long baselines and reduces relative systematic uncertainties between detectors and nuclear reactors. This paper describes the assembly and installation of the Daya Bay antineutrino detectors.

Study of dielectronic recombination at the CSRm using lithium-like Ar15+ ions

The main cooler storage ring (CSRm) of the HIRFL facility in Lanzhou, China is equipped with an electron-cooler and denotes an ideal platform for dielectronic recombination (DR) experiments. In order to fully understand our DR experimental setup and especially the electron energy detuning system, we have performed a DR calibration experiment using the Li-like argon ions at the CSRm because Ar15+ has a simple electronic structure and the DR spectrum can be calculated with an ultra-high precision and be compared with the existing experimental data. The experiment was carried out over the center-of-mass energy range 0–32 eV that includes all DR resonance associated with 2S1/2 → 2p1/2 and most of the 2S1/2 → 2p3/2 excitations. We present the details of the experimental technique and the DR experimental resonance spectrum of the Ar15+.

Laser cooling of relativistic heavy-ion beams for FAIR

Laser cooling is a powerful technique to reduce the longitudinal momentum spread of stored relativistic ion beams. Based on successful experiments at the experimental storage ring at GSI in Darmstadt, of which we show some important results in this paper, we present our plans for laser cooling of relativistic ion beams in the future heavy-ion synchrotron SIS100 at the Facility for Antiproton and Ion Research in Darmstadt.

Double-electron capture in relativistic U92+ collisions at the ESR gas-jet target

Abstract Total cross-sections for radiative single- and double-electron capture are measured in collisions of fast highly charged ions with light target atoms. Cross-sections for non-correlated double capture are in accordance with theoretical predictions. No significant line structure at twice the single K-radiative electron capture (K-REC) photon energy was observed. Angular distributions single K-REC photons associated with single- and double-charge exchange exhibit the same pattern. The corresponding REC lines are almost by a factor of two broader for double-charge exchange than in the single capture case.

The first test experiment performed at the electron cooler of storage rings in Lanzhou

The cooler storage ring (CSR) project was launched in 2000 at the Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou. In 2007, the installation was completed and the commissioning of CSRs gained great success, a new highly precise generation of collision experiments will become accessible even for the heaviest ion species. A commissioning RR experiment was performed at the electron cooler with Ar18+ ions, the results are reported. And the further development of the experiments at cooler will be discussed.

Proposal for precision determination of 7.8 eV isomeric state in 229Th at heavy ion storage ring

The ultraviolet optical transition of the isomeric state in 229Th has attracted much attention recently due to its potential application to building an atomic/nuclear clock with ultra-high precision. However, the lowest nuclear excitation energy and the lifetime of the first excited state of 229Th were not measured directly and precisely until now, and how to precisely determine this isomer state of the 229Th is an urgent requirement. Here an experimental approach of using a technique similar to that of dielectronic recombination to measure the transition energy of the isomer state of 229Th at heavy ion storage rings is described. It is expected that the resonant transition can be found and determined with a precision better than several milli-eV.

Signatures of the projectile electron–target core elastic scattering in Ar (e, 2e) reactions at low and intermediate impact energies

The momentum distributions of the recoil ions Ar+ in Ar (e, 2e) reactions are obtained at incident electron energies from 80 to 220 eV by using the reaction microscope. The contributions of large longitudinal momentum corresponding to the large scattering angle are significant. By comparing the single differential cross sections of the Ar (e, 2e) with those of the electron–argon elastic scattering process, it is concluded that the elastic scattering between the incident electron and the target core plays an important role in the large angle ionization scattering process, and the additional phase shift introduced by the ionized electron results in the disappearance of the sharp minimum that was observed in the elastic scattering. A qualitative explanation of the bigger relative contributions of recoil ions with large longitudinal momenta in Ne (e, 2e) compared to the case in Ar (e, 2e) is given.