New mass anchor points for neutron-deficient heavy nuclei from direct mass measurements of radium and actinium isotopes

TL;DR

This study provides new direct mass measurements of radium and actinium isotopes, establishing anchor points for nuclear models and benchmarks near the N=126 shell closure, with results generally confirming previous indirect data.

Contribution

It presents the first direct mass measurements of specific radium and actinium isotopes, offering new benchmarks for nuclear structure near the N=126 shell closure.

Findings

Mass measurements agree with previous indirect data

New anchor points for U and Np nuclei near N=126

Discussion of potential mass ambiguities from decay data

Abstract

The masses of the exotic isotopes $^{210-214}$Ac and $^{210-214}$Ra have been measured with a multi-reflection 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 $\alpha$-$\gamma$ 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 $Z=92$ sub-shell 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.