| Atomic nuclei are many-body quantum systems composed of two distinct types of fermion: proton and neutron. Mass is one of the fundamental properties of that system, and it reflects the total complex effect of strong, weak and electromagnetic interactions among nucleons. Hence, nuclear mass plays an essential role in our understanding of nuclear structure and the origin of elements in the cosmos. However,the precision mass measurements of exotic nuclei far away from the β-stability line are strongly restricted by their low production rates and short half-lives. Isochronous Mass Spectrometry(IMS), based on a heavy-ion storage ring, has been proven to be a powerful tool for mass measurement of exotic nuclei.In this thesis, the first IMS experiment of neutron-rich nuclides conducted at HIRFL-CSR was reported. In the IMS experiment, the primary beam of86Kr28+was accumulated and accelerated to an energy of 460.65 Me V/u in the synchrotron CSRm.The86Kr28+ions were fast extracted and focused on a ～ 15 mm thick beryllium target which was placed at the entrance of the RIBLL2(an in-flight fragment separator).The hot fragments, produced via projectile fragmentation of86Kr28+, were separated by the RIBLL2 and then injected and stored in the experimental cooler storage ring CSRe. A time-of-flight(TOF) detector, which was installed in the CSRe, was applied to measure the revolution time of the stored ions. The mass values of the nuclides of interest were calibrated from the revolution time spectrum.The resolving power of IMS was weakened by the instabilities of magnetic fields which cause small shifts of the entire revolution time spectrum measured for different injections. In our data analysis, a new method called weighted-shift correction wasused to minimize the effect of such instabilities, and thus the resulting mass resolving power(m/?m)≈ 8.2 × 104 was achieved. Masses of 16 nuclides were remeasured with uncertainty comparable with the corresponding values reported in AME12. Most of our results are in good agreement with the literature ones at the 1σ confidence level except four nuclides52-54 Sc and56 Ti. With our new results, the large increasing in binding energy of53 Sc and54Sc suggest the persistence of new neutron magic number N=32 in Sc isotopes, and the N = 32 shell closure strength in Sc isotopes is comparable with the one in Ca isotopes.We also investigate the performance of the IMS using the exist experimental results. The six-dimension phase-space linear transmission theory was employed to simulate the motion of stored ions in the CSRe. Base on the simulation work, we reproduced the result of a former IMS experiment for58 Ni projectile fragments. Moreover, the large systematic deviation in the calibration procedure for that experiment was found to be caused by the disparity of injected moment distribution shape and the difference of energy loss in detector for different ion-species.To reduce the systematic deviation and to improve the mass resolving power, we realize the concept of an isochronous mass spectrometry(IMS) applying two time-offlight(TOF) detectors that was originated many years ago at GSI. The corresponding method for data analysis was also discussed in detail. The new data analyisis method was applied to a series of simulated data. The results showed that the IMS with two TOF detectors can improve the mass resolving power without limiting the acceptance of the ring. Comparing to the IMS with only one TOF detector, the mass resolving power of the upgraded IMS with two TOF detectors can be significantly improved especially for the nuclei with Lorentz factor γ far away from transition point γtof the storage ring. The mass resolving power of the IMS with two TOF detectors is dominantly limited by the performance of the two TOF detectors. |
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