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

B. Liu, M. Brodeur, J. A. Clark, D. Ray, G. Savard, A. A. Valverde, D. P. Burdette, A. M. Houff, A. Mitra, G. E. Morgan, R. Orford, W. S. Porter, C. Quick, F. Rivero, K. S. Sharma, L. Varriano

TL;DR

This study reports high-precision PI-ICR Penning-trap mass measurements of $^{149}$La, $^{149}$Ce, and $^{149}$Pr at CARIBU, revealing a significantly more bound $^{149}$La mass than a recent JYFLTRAP result and providing eightfold improved precision for $^{149}$Ce and $^{149}$Pr. The $^{149}$La result is independently corroborated by a concurrent MR-TOF measurement, while $^{149}$Ce agrees with AME2020 and $^{149}$Pr lies modestly below AME2020 with MR-TOF validation. These measurements shift the understanding of the $A=149$ mass surface and alter the inferred $S_{2n}$ trends across the La–Ce–Pr chain, offering robust, cross-validated data essential for nuclear-structure studies near the region. The work demonstrates the effectiveness of PI-ICR with CPT and corroborates mass values through multiple, independent techniques.

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 $β$-time of flight detector at RIKEN, providing further validation of the present results.

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

TL;DR

This study reports high-precision PI-ICR Penning-trap mass measurements of La, Ce, and Pr at CARIBU, revealing a significantly more bound La mass than a recent JYFLTRAP result and providing eightfold improved precision for Ce and Pr. The La result is independently corroborated by a concurrent MR-TOF measurement, while Ce agrees with AME2020 and Pr lies modestly below AME2020 with MR-TOF validation. These measurements shift the understanding of the mass surface and alter the inferred trends across the La–Ce–Pr chain, offering robust, cross-validated data essential for nuclear-structure studies near the region. The work demonstrates the effectiveness of PI-ICR with CPT and corroborates mass values through multiple, independent techniques.

Abstract

Penning trap mass measurements of La, Ce, and 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 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 Ce and Pr are determined with an eight-fold improvement in precision compared to previous time-of-flight ion-cyclotron-resonance measurements; the Ce value is consistent with AME2020, while the Pr mass excess is lower by 17.5 keV. The mass excesses of La and Pr reported in this work have been confirmed recently by a measurement with a multi-reflection time-of-flight mass spectrometer coupled to a -time of flight detector at RIKEN, providing further validation of the present results.
Paper Structure (6 sections, 3 equations, 4 figures, 1 table)

This paper contains 6 sections, 3 equations, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. Experiment setup
  3. Measurement method
  4. Experimental details and data analysis methods
  5. Measurement results and discussion
  6. Conclusion

Figures (4)

  • Figure 1: Typical count histograms recorded during the measurement of $^{149}$La, where both $^{149}$La and $^{149}$Ce were present in the trap. The sparse counts distributed around are attributed primarily to background noise.
  • Figure 2: Measured cyclotron frequency of $^{149}$Ce as a function of accumulation time $t_\mathrm{{acc}}$ from 486 ms to 487 ms. The dashed red curve shows a sinusoidal fit of the data. The horizontal green line marks the mean cyclotron frequency extracted from the fit. The yellow shaded band represent the fit uncertainty of the mean frequency, while the wider green band is the fit uncertainty scaled by the $\sqrt{\chi^2}$=1.41 from the fit.
  • Figure 3: Mass excess difference between this work and the AME2020 AME2020 ground state for $^{149}$La, $^{149}$Ce, and $^{149}$Pr. The solid red line and red shaded bands indicate the AME2020 ground state value and uncertainty range. Results from this work are compared with all experimental data present in AME2020: 2006 Savard2006, 2003 02ShB, 1987 87GrA, 1995 95Ik03, 1967 67Va14. The measurement results from JYFLTRAP Jaries2025 and RIKEN Kimura2025 are also shown for comparison.
  • Figure 4: Two-neutron separation energies $S_{2n}$ for the isotopic chains of Ba, La, Ce, Pr, and Nd from the AME2020 AME2020. Also shown are recent JYFLTRAP results for the La chain, and CPT results Orford2019PhdOrford2022Ray2024 for the La, Ce and Pr chains. $S_{2n}$-values affected by measurements from this work are circled.