Precise Mass Measurement of the $^{149}$La-$^{149}$Ce-$^{149}$Pr isobaric chain

TL;DR

This study presents highly precise mass measurements of the isotopes $^{149}$La, $^{149}$Ce, and $^{149}$Pr using Penning trap techniques, revealing significant differences from previous data and refining nuclear mass models.

Contribution

The paper provides the first high-precision mass measurements of these isotopes with a phase-imaging ion-cyclotron-resonance technique, improving accuracy and confirming results with independent methods.

Findings

Mass excess of $^{149}$La differs by 221 keV from recent measurements.

Mass excesses of $^{149}$Ce and $^{149}$Pr are determined with eight-fold improved precision.

Results are consistent with some previous data and validated by independent measurements.

Abstract

Penning trap mass measurements of $^{149}$La, $^{149}$Ce, and $^{149}$Pr were performed with the Canadian Penning Trap (CPT) at the CARIBU facility of Argonne National Laboratory using the phase-imaging ion-cyclotron-resonance technique. The resulting mass excess of $^{149}$La differs by 221 keV from a recent JYFLTRAP measurement, resulting in a significant change in the profile of the two-neutron separation energy for that isotopic chain. The mass excesses of $^{149}$Ce and $^{149}$Pr are determined with an eight-fold improvement in precision compared to previous time-of-flight ion-cyclotron-resonance measurements; the $^{149}$Ce value is consistent with AME2020, while the $^{149}$Pr mass excess is lower by 17.5 keV. The mass excesses of $^{149}$La and $^{149}$Pr reported in this work have been confirmed recently by a measurement with a multi-reflection time-of-flight mass spectrometer coupled to a $\beta$-time of flight detector at RIKEN, providing further validation of the present results.