The masses of the exotic isotopes ${}^{210-214}\mathrm{Ac}$ and ${}^{210-214}\mathrm{Ra}$ have been measured with a multireflection time-of-flight mass spectrograph. These isotopes were obtained in flight as fusion-evaporation products behind the gas-filled recoil ion separator GARIS-II at RIKEN. The new direct mass measurements serve as an independent and direct benchmark for existing $\alpha \text{−}\gamma$ spectroscopy data in this mass region. Further, new mass anchor points are set for U and Np nuclei close to the $N=126$ shell closure for a future benchmark of the $Z=92$ subshell for neutron-deficient heavy isotopes. Our mass results are in general in good agreement with the previously indirectly determined mass values. Together with the measurement data, reasons for possible mass ambiguities from decay-data links between ground states are discussed.

• Received 9 January 2018
• Revised 19 April 2018

DOI:https://doi.org/10.1103/PhysRevC.97.064306