Mass Measurement of 27^{27}P for Improved Type-I X-ray Burst Modeling

Light curves are the primary observable of type-I x-ray bursts. Computational x-ray burst models must match simulations to observed light curves. Most of the error in simulated curves comes from uncertainties in $rp$ process reaction rates, which can be reduced via precision mass measurements of neutron-deficient isotopes in the $rp$ process path. We perform a precise atomic mass measurement of $^{27}$P and use this new measurement to update existing type-I x-ray burst models to produce an improved light curve. High-precision Penning trap mass spectrometry was used to determine the atomic mass of $^{27}$P. Modules for Experiments in Stellar Astrophysics (MESA) was then used to simulate x-ray bursts using a 1D multi-zone model to produce updated light curves. The mass excess of $^{27}$P was measured to be -670.7$\pm$ 0.6 keV, a fourteen-fold precision increase over the mass reported in AME2020. The $^{26}$Si($p, \gamma$)$^{27}$P and reverse photodisintegration reaction rates have been determined to a higher precision based on the new, high precision mass measurement of $^{27}$P, and MESA light curves generated using these rates. Changes in the mass of $^{27}$P seem to have minimal effect on XRB light curves, even in burster systems tailored to maximize impact. The mass of $^{27}$P does not play a significant role in x-ray burst light curves. It is important to understand that more advanced models don't just provide more precise results, but often qualitatively different ones. This result brings us a step closer to being able to extract stellar parameters from individual x-ray burst observations. In addition, the Isobaric Multiplet Mass Equation (IMME) has been validated for the $A=27, T=3/2$ quartet, but only after including a small, theoretically predicted cubic term and utilizing an updated excitation energy for the $T=3/2$ isobaric analogue state of $^{27}$Si.Comment: 8 pages, 7 figure

Measurements and computational analysis of the natural decay of Lu 176

Background: Mainly because of its long half-life and despite its scientific relevance, spectroscopic measurements of Lu176 forbidden β decays are very limited and lack formulation of shape factors. A direct precise measurement of its Q value is also presently unreported. In addition, the description of forbidden decays provides interesting challenges for nuclear theory. The comparison of precise experimental results with theoretical calculations for these decays can help to test underlying models and can aid the interpretation of data from other experiments. Purpose: Perform the first precision measurements of Lu176β-decay spectra and attempt the observation of its electron capture decays, as well as perform the first precision direct measurement of the Lu176β-decay Q value. Compare the shape of the precisely determined experimental β spectra to theoretical calculations, and compare the end point energy to that obtained from an independent Q value measurement. Method: The Lu176β-decay spectra measurements and the search for electron capture decays were performed with an experimental setup that employed lutetium-containing scintillator crystals and a NaI(Tl) spectrometer for coincidence counting. The β decay Q value was determined via high-precision Penning trap mass spectrometry (PTMS) with the LEBIT facility at the National Superconducting Cyclotron Laboratory. The β-spectrum calculations were performed within the Fermi theory formalism with nuclear structure effects calculated using a shell model approach. Results: Both β transitions of Lu176 were experimentally observed and corresponding shape factors formulated in their entire energy ranges. The search for electron capture decay branches led to an experimental upper limit of 6.3×10-6 relative to its β decays. The Lu176β-decay and electron capture Q values were measured using PTMS to be 1193.0(6) and 108.9(8) keV, respectively. This enabled precise β end point energies of 596.2(6) and 195.3(6) keV to be determined for the primary and secondary β decays, respectively. The conserved vector current hypothesis was applied to calculate the relativistic vector matrix elements. The β-spectrum shape was shown to significantly depend on the Coulomb displacement energy and on the value of the axial vector coupling constant gA, which was extracted according to different assumptions. Conclusion: The implemented self-scintillation method has provided unmatched observations of Lu176, independently validated by the first direct measurements of its β-decay Q value by Penning trap mass spectrometry. Theoretical study of the main β transition led to the extraction of very different effective gA and log10f values, showing that a high-precision description of this transition would require a realistic nuclear structure with nucleus deformation. </p

Direct determination of the 138^{138}La β-decay Q value using Penning trap mass spectrometry

International audienceBackground: The understanding and description of forbidden decays provides interesting challenges for nuclear theory. These calculations could help to test underlying nuclear models and interpret experimental data. Purpose: Compare a direct measurement of the La138β-decay Q value with the β-decay spectrum end-point energy measured by Quarati et al. using LaBr3 detectors [Appl. Radiat. Isot. 108, 30 (2016)ARISEF0969-804310.1016/j.apradiso.2015.11.080]. Use new precise measurements of the La138β-decay and electron capture (EC) Q values to improve theoretical calculations of the β-decay spectrum and EC probabilities. Method: High-precision Penning trap mass spectrometry was used to measure cyclotron frequency ratios of La138, Ce138, and Ba138 ions from which β-decay and EC Q values for La138 were obtained. Results: The La138β-decay and EC Q values were measured to be Qβ=1052.42(41) keV and QEC=1748.41(34) keV, improving the precision compared to the values obtained in the most recent atomic mass evaluation [Wang , Chin. Phys. C 41, 030003 (2017)1674-113710.1088/1674-1137/41/3/030003] by an order of magnitude. These results are used for improved calculations of the La138β-decay shape factor and EC probabilities. New determinations for the Ce138 2EC Q value and the atomic masses of La138, Ce138, and Ba138 are also reported. Conclusion: The La138β-decay Q value measured by Quarati et al. is in excellent agreement with our new result, which is an order of magnitude more precise. Uncertainties in the shape factor calculations for La138β decay using our new Q value are reduced by an order of magnitude. Uncertainties in the EC probability ratios are also reduced and show improved agreement with experimental data

Direct determination of the la 138 β -decay Q value using Penning trap mass spectrometry

Background: The understanding and description of forbidden decays provides interesting challenges for nuclear theory. These calculations could help to test underlying nuclear models and interpret experimental data. Purpose: Compare a direct measurement of the La138β-decay Q value with the β-decay spectrum end-point energy measured by Quarati et al. using LaBr3 detectors [Appl. Radiat. Isot. 108, 30 (2016)ARISEF0969-804310.1016/j.apradiso.2015.11.080]. Use new precise measurements of the La138β-decay and electron capture (EC) Q values to improve theoretical calculations of the β-decay spectrum and EC probabilities. Method: High-precision Penning trap mass spectrometry was used to measure cyclotron frequency ratios of La138, Ce138, and Ba138 ions from which β-decay and EC Q values for La138 were obtained. Results: The La138β-decay and EC Q values were measured to be Qβ=1052.42(41) keV and QEC=1748.41(34) keV, improving the precision compared to the values obtained in the most recent atomic mass evaluation [Wang, Chin. Phys. C 41, 030003 (2017)1674-113710.1088/1674-1137/41/3/030003] by an order of magnitude. These results are used for improved calculations of the La138β-decay shape factor and EC probabilities. New determinations for the Ce138 2EC Q value and the atomic masses of La138, Ce138, and Ba138 are also reported. Conclusion: The La138β-decay Q value measured by Quarati et al. is in excellent agreement with our new result, which is an order of magnitude more precise. Uncertainties in the shape factor calculations for La138β decay using our new Q value are reduced by an order of magnitude. Uncertainties in the EC probability ratios are also reduced and show improved agreement with experimental data.RST/Luminescence Material

Measurements and computational analysis on the natural decay of 176^{176}Lu

International audienceBackground: Mainly because of its long half-life and despite its scientific relevance, spectroscopic measurements of 176Lu beta decays are very limited and lack formulation of shape factors. Direct measurement of its Q-value is also presently unreported. In addition, the description of forbidden decays provides interesting challenges for nuclear theory. The comparison of precise experimental results with theoretical calculations for these decays can help to test underlying models and can aid the interpretation of data from other experiments.Purpose: Perform the first precision measurement of 176Lu beta-decay spectrum and attempt the observation of its electron capture decays, as well as perform the first precision direct measurement of the 176Lu beta-decay Q-value. Compare the shape of the precisely determined experimental beta-spectrum to theoretical calculations, and compare the end-point energy to that obtained from an independent Q-value measurement.Method: The 176Lu beta-decay spectra and the search for electron capture decays were measured with an experimental set-up that employed lutetium-based scintillator crystals and an NaI(Tl) spectrometer for coincidence counting. The beta-decay Q-value was determined via high-precision Penning trap mass spectrometry (PTMS) with the LEBIT facility at the National Superconducting Cyclotron Laboratory. The beta-spectrum calculations were performed within the Fermi theory formalism with nuclear structure effects calculated using a shell model approach.Results: Both beta transitions of 176Lu were experimentally observed and corresponding shape factors formulated in their entire energy ranges. Search for electron captures decay branches led to an experimental upper limit of 6.3x10-6 compared to its beta decays. The 176Lu beta-decay and electron capture Q-values were measured using PTMS to be 1193.0(6) keV and 108.9(8) keV, respectively. This enabled precise beta end-point energies of 596.2(6) keV and 195.3(6) keV for the primary and secondary beta-decays, respectively, to be determined. The conserved vector current hypothesis was applied to calculate the relativistic vector matrix elements. The beta-spectrum shape was shown to significantly depend on the Coulomb displacement energy and on the value of the axial vector coupling constant gA, which was extracted according to different assumptions

Precision mass measurements of neutron-rich Co isotopes beyond N = 40

The region near Z=28, N=40 is a subject of great interest for nuclear structure studies due to spectroscopic signatures in $^{68}$Ni suggesting a subshell closure at N=40. Trends in nuclear masses and their derivatives provide a complementary approach to shell structure investigations via separation energies. Penning trap mass spectrometry has provided precise measurements for a number of nuclei in this region, however a complete picture of the mass surfaces has so far been limited by the large uncertainty remaining for nuclei with N > 40 along the iron and cobalt chains. Here we present the first Penning trap measurements of $^{68,69}$Co, performed at the Low-Energy Beam and Ion Trap facility at the National Superconducting Cyclotron Laboratory. In addition, we perform ab initio calculations of ground state and two-neutron separation energies of cobalt isotopes with the valence-space in-medium similarity renormalization group approach based on a particular set of two- and three-nucleon forces which predict saturation in infinite matter. We discuss the importance of these measurements and calculations for understanding the evolution of nuclear structure near $^{68}$Ni.Comment: 7 pages, 6 figure

High-precision mass measurements of the isomeric and ground states of 44^{44}V : Improving constraints on the isobaric multiplet mass equation parameters of the A=44 , 0+^+ quintet

Background: The quadratic isobaric multiplet mass equation (IMME) has been very successful at predicting the masses of isobaric analog states in the same multiplet, while its coefficients are known to follow specific trends as functions of mass number. The Atomic Mass Evaluation 2016 [Chin. Phys. C 41, 030003 (2017)]1674-113710.1088/1674-1137/41/3/030003 V44 mass value results in an anomalous negative c coefficient for the IMME quadratic term; a consequence of large uncertainty and an unresolved isomeric state. The b and c coefficients can provide useful constraints for construction of the isospin-nonconserving Hamiltonians for the pf shell. In addition, the excitation energy of the 0+,T=2 level in V44 is currently unknown. This state can be used to constrain the mass of the more exotic Cr44. Purpose: The aim of the experimental campaign was to perform high-precision mass measurements to resolve the difference between V44 isomeric and ground states, to test the IMME using the new ground state mass value and to provide necessary ingredients for the future identification of the 0+, T=2 state in V44. Method: High-precision Penning trap mass spectrometry was performed at LEBIT, located at the National Superconducting Cyclotron Laboratory, to measure the cyclotron frequency ratios of [VO44g,m]+ versus [SCO32]+, a well-known reference mass, to extract both the isomeric and ground state masses of V44. Results: The mass excess of the ground and isomeric states in V44 were measured to be −23804.9(80) keV/c2 and −23537.0(55) keV/c2, respectively. This yielded a new proton separation energy of Sp=1773(10) keV. Conclusion: The new values of the ground state and isomeric state masses of V44 have been used to deduce the IMME b and c coefficients of the lowest 2+ and 6+ triplets in A=44. The 2+c coefficient is now verified with the IMME trend for lowest multiplets and is in good agreement with the shell-model predictions using charge-dependent Hamiltonians. The mirror energy differences were determined between V44 and Sc44, in line with isospin-symmetry for this multiplet. The new value of the proton separation energy determined, to an uncertainty of 10 keV, will be important for the determination of the 0+, T=2 state in V44 and, consequently, for prediction of the mass excess of Cr44