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Orrigo, S. E. A. et al, Rubio, B., Gelletly, W., Aguilera, P., Algora, A., Morales, A. I., et al. (2021). beta decay of the very neutron-deficient Ge-60 and Ge-62 nuclei. Phys. Rev. C, 103(1), 014324–12pp.
Abstract: We report here the results of a study of the beta decay of the proton-rich Ge isotopes, Ge-60 and Ge-62, produced in an experiment at the RIKEN Nishina Center. We have improved our knowledge of the half-lives of Ge-62 [73.5(1) ms] and Ge-60 [25.0(3) ms] and its daughter nucleus, Ga-60 [69.4(2) ms]. We measured individual beta-delayed proton and gamma emissions and their related branching ratios. Decay schemes and absolute Fermi and Gamow-Teller transition strengths have been determined. The mass excesses of the nuclei under study have been deduced. A total beta-delayed proton-emission branching ratio of 67(3)% has been obtained for Ge-60. New information has been obtained on the energy levels populated in Ga-60 and on the 1/2(-) excited state in the beta p daughter Zn-59. We extracted a ground state-to-ground state feeding of 85.3(3)% for the decay of Ge-62. Eight new y lines have been added to the deexcitation of levels populated in the Ga-62 daughter.
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Dombos, A. C. et al, & Algora, A. (2021). Total absorption spectroscopy of the beta decay of Zr-101,102 and Tc-109. Phys. Rev. C, 103(2), 025810–20pp.
Abstract: The beta decay of Zr-101,Zr-102 and Tc-109 was studied using the technique of total absorption spectroscopy. The experiment was performed at the National Superconducting Cyclotron Laboratory using the Summing NaI(Tl) (SuN) detector in the first-ever application of total absorption spectroscopy with a fast beam produced via projectile fragmentation. The beta-decay feeding intensity and Gamow-Teller transition strength distributions were extracted for these three decays. The extracted distributions were compared to three different quasiparticle random-phase approximation (QRPA) models based on different mean-field potentials. A comparison with calculations from one of the QRPA models was performed to learn about the ground-state shape of the parent nucleus. For Zr-101 and Zr-102, calculations assuming a pure shape configuration (oblate or prolate) were not able to reproduce the extracted distributions. These results may indicate that some type of mixture between oblate and prolate shapes is necessary to reproduce the extracted distributions. For Tc-109, a comparison of the extracted distributions with QRPA calculations suggests a dominant oblate configuration. The other two QRPA models are commonly used to provide beta-decay properties in r-process network calculations. This work shows the importance of making comparisons between the experimental and theoretical beta-decay distributions, rather than just half-lives and beta-delayed neutron emission probabilities, as close to the r-process path as possible.
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Gombas, J., DeYoung, P. A., Spyrou, A., Dombos, A. C., Algora, A., Baumann, T., et al. (2021). beta-decay feeding intensity distributions for Nb-103,Nb-104m. Phys. Rev. C, 103(3), 035803–8pp.
Abstract: The beta decays of Nb-103,Nb-104m were studied with the Summing NaI(Tl) (SuN) detector at the National Superconducting Cyclotron Laboratory. The beta-decay feeding intensity distribution I-beta(E) for each isotope was extracted by measuring gamma rays in coincidence with an emitted electron. The I-beta(E) was extracted via the total absorption spectroscopy technique. The I-beta(E) for each nucleus was compared to predictions made by the quasiparticle random-phase approximation (QRPA) model which is commonly used to calculate beta-decay properties for astrophysical applications. The main goal was to provide experimental data for neutron-rich nuclei, relevant to the astrophysical r process. In addition, the extracted beta-decay feeding intensity distributions can lead to a better understanding of nuclear structure in a region of rapid structure changes around A = 100. Finally, experimental data for Nb-104m are also of interest to antineutrino studies of nuclear reactors.
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n_TOF Collaboration(Dietz, M. et al), Domingo-Pardo, C., & Tain, J. L. (2021). Measurement of the Ge-72(n, y) cross section over a wide neutron energy range at the CERN n_TOF facility. Phys. Rev. C, 103(4), 045809–8pp.
Abstract: The Ge-72(n, gamma) cross section was measured for neutron energies up to 300 keV at the neutron time-of-flight facility n_TOF (CERN), Geneva, for the first time covering energies relevant to heavy-element synthesis in stars. The measurement was performed at the high-resolution beamline EAR-1, using an isotopically enriched (GeO2)-Ge-72 sample. The prompt capture gamma rays were detected with four liquid scintillation detectors, optimized for low neutron sensitivity. We determined resonance capture kernels up to a neutron energy of 43 keV, and averaged cross sections from 43 to 300 keV. Maxwellian-averaged cross section values were calculated from kT = 5 to 100 keV, with uncertainties between 3.2% and 7.1%. The new results significantly reduce uncertainties of abundances produced in the slow neutron capture process in massive stars.
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Moon, B. et al, & Montaner-Piza, A. (2021). Nuclear structure of Te isotopes beyond neutron magic number N=82. Phys. Rev. C, 103(3), 034320–15pp.
Abstract: Newly observed decay schemes of the nuclei Sb-137 and Sb-138 are reported. The neutron-rich Sb isotopes were produced by the in-flight fragmentation of a U-238 primary beam with an energy of 345 MeV/nucleon. Several new excited states of Te-137 with tentatively assigned spin-parities of (5/2(-)), (9/2(-)), and (7/2) have been established which play an important role in the evolution of neutron levels beyond N = 82. The study of the beta decay of Sb-138 led to a considerable extension of the level scheme of Te-138 including the identification of several nonyrast states. The structure of Te-137 and Te-138 is discussed on the basis of large-scale shell-model calculations performed using two different effective interactions.
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