Precision Mass Measurements at the Storage Ring Facility in Lanzhou

The Institute of Modern Physics (IMP), Chinese Academy of Sciences (CAS), has been working on mass measurements of nuclides with Isochronous Mass Spectrometry at the Cooler-Storage Ring at the Heavy Ion Research Facility (HIRFL-CSR) in Lanzhou since 2007. Similar to the SIS-ESR facility at GSI, the HIRFL-CSR consists of the main cooler-storage ring (CSRm) and the experimental storage ring (CSRe), which are connected by the in-flight fragment separator RIBLL2. The primary beam can be accumulated and then accelerated to high energy in CSRm. The high-energy beam is fast extracted from CSRm and focused upon a beryllium target to produce fragments. After in-flight separation of the fragments in RIBLL2, the exotic nuclei of interest are injected into CSRe, which is tuned into an isochronous ion-optical mode. Beams of 36Ar, 58Ni, 78Kr, 84Kr and 112Sn have been used to produce exotic nuclides. About twenty mass excesses of proton-rich nuclei were determined directly for the first time with improved detection and data analysis techniques at CSRe. A mass resolving power of 170000 has been achieved. These mass data have been used to study nuclear structure and nuclear astrophysics, e.g., to test Isobaric Multiplet Mass Equation (IMME) with mass excess of 53Ni and to study the 64Ge waiting point in the rp-process with mass excess of 65As.