Experimental Study on the Systematic Deviation in the Conventional Isochronous Mass Spectrometry

Storage-ring-based isochronous mass spectrometry(IMS) is an effective tool for mass measurements of nuclei far from stability line. However, in the mass measurements of neutron-deficient nuclei with conventional IMS, systematic deviation of mass determination was observed when nuclei with T_z^=-1/2 and T_z^=-1 in a wide revolution time range were measured. In this work, the revolution time and velocity of stored ions were measured simultaneously by using two time-of-flight(TOF) detectors installed in a straight section of CSRe. Using these experimental information, systematic deviation in conventional IMS was investigated experimentally. The systematic deviation is found to be caused by the different asymmetric distributions of momentum of the stored ions and the non-constant storage ring energy transition parameter \gamma_\rm t^, and it can be eliminated by limiting the momentum acceptance during offline data processing. This study provides valuable reference and significant guidance for mass measurements using conventional IMS.