We report the mass measurements of neutron-rich isotopes produced via spontaneous fission of ${ }^{ 252}$Cf using a multi-reflection time-of-flight mass spectrograph. The mass of ${ }^{ 155}$Ce is determined experimentally for the first time. A discrepancy between the experimental and literature values was found for the mass of ${ }^{ 127}$Sb, which was previously deduced through indirect measurements. In comparison with several theoretical predictions, both the values and the trend of the mass excesses of ${ }^{ 152-155}$Ce cannot be consistently explained. The wide-range and simultaneous mass measurements of the multi-reflection time-of-flight mass spectrograph enable us to cross-check the existing mass data, and the conflict between the measured time-of-flight ratio and the extracted mass would imply the necessity of reexamining them.
Categories: nucl-ex