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Wasilewska, B. et al, & Gaudilla, V. (2022). gamma decay to the ground state from the excitations above the neutron threshold in the Pb-208(p, p ' gamma) reaction at 85 MeV. Phys. Rev. C, 105(1), 014310–7pp.
Abstract: A new measurement of gamma decay from the states above the neutron threshold in Pb-208 has been performed at Cyclotron Centre Bronowice in Krakow, Poland. The main goal of the experiment was to observe the gamma decay to the ground state from the isoscalar giant quadrupole resonance (ISGQR). To this day, the only published observation of this phenomenon dates back to the late 1980s, where gamma decay to the ground state branching ratio was reported. At variance with the existing measurement using inelastic scattering of O-17, here proton inelastic scattering is employed. In particular, data were obtained for Pb-208(p, p'gamma) at 85 MeV beam energy, where gamma rays were measured for proton scattering angles 8.9 degrees, 10.7 degrees, 12.5 degrees, and 14.3 degrees. By applying a similar analysis method as in the previous experiment, the branching ratio of ISGQR gamma decay to the ground state was extracted from the data.
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n_TOF Collaboration(Lederer-Woods, C. et al.), Domingo-Pardo, C., & Tain, J. L. (2021). Destruction of the cosmic gamma-ray emitter Al-26 in massive stars: Study of the key Al-26(n, alpha) reaction. Phys. Rev. C, 104(3), L032803–6pp.
Abstract: Neutron destruction reactions of the cosmic gamma-ray emitter Al-26 are of importance to determine the amount of Al-26 ejected into our galaxy by supernova explosions and for Al-26 production in asymptotic giant branch stars. We performed a new measurement of the Al-26(n, alpha) reaction up to 160-keV neutron energy at the neutron time-of-flight facilities n_TOF at CERN and GELINA at EC-JRC. We provide strengths for ten resonances, six of them for the first time. We use our data to calculate astrophysical reactivities for stellar temperatures up to 0.7 GK. Our results resolve a discrepancy between the two previous direct measurements of this reaction, and indicate higher stellar destruction rates than the most recently recommended reactivity.
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n_TOF Collaboration(Lederer-Woods, C. et al.), Domingo-Pardo, C., & Tain, J. L. (2021). Destruction of the cosmic gamma-ray emitter Al-26 in massive stars: Study of the key Al-26(n, p) reaction. Phys. Rev. C, 104(2), L022803–7pp.
Abstract: The Al-26(n, p) Mg-26 reaction is the key reaction impacting on the abundances of the cosmic gamma-ray emitter Al-26 produced in massive stars and impacts on the potential pollution of the early solar system with Al-26 by asymptotic giant branch stars. We performed a measurement of the Al-26(n, p) Mg-26 cross section at the high-flux beam line EAR-2 at the n_TOF facility (CERN). We report resonance strengths for eleven resonances, nine being measured for the first time, while there is only one previous measurement for the other two. Our resonance strengths are significantly lower than the only previous values available. Our cross-section data range to 150 keV neutron energy, which is sufficient for a reliable determination of astrophysical reactivities up to 0.5 GK stellar temperature.
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AGATA Collaboration(Liu, X. et al), Gadea, A., Jurado, M., Domingo-Pardo, C., Huyuk, T., & Perez-Vidal, R. M. (2021). Evidence for enhanced neutron-proton correlations from the level structure of the N = Z+1 nucleus Tc-87(43)44. Phys. Rev. C, 104(2), L021302–5pp.
Abstract: The low-lying excited states in the neutron-deficient N = Z + 1 nucleus (87)(43)Tcc(44) have been studied via the fusion-evaporation reaction Fe-54(Ar-36, 2n1p)Tc-87 at the Grand Accelerateur National d'Ions Lourds (GANIL), France. The AGATA spectrometer was used in conjunction with the auxiliary NEDA, Neutron Wall, and DIAMANT detector arrays to measure coincident prompt gamma rays, neutrons, and charged particles emitted in the reaction. A level scheme of Tc-87 from the (9/2(g.s.)(+)) state to the (33/2(1)(+)) state was established based on six mutually coincident gamma-ray transitions. The constructed level structure exhibits a rotational behavior with a sharp backbending at (h) over bar omega approximate to 0.50 MeV. A decrease in alignment frequency and increase in alignment sharpness in the odd-mass isotonic chains around N = 44 is proposed as an effect of the enhanced isoscalar neutron-proton interactions in odd-mass nuclei when approaching the N = Z line.
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Fernandez, A. et al, Gadea, A., Perez-Vidal, R. M., Jurado, M., & Domingo-Pardo, C. (2021). Reinterpretation of excited states in Po-212: Shell-model multiplets rather than alpha-cluster states. Phys. Rev. C, 104(5), 054316–19pp.
Abstract: A gamma-ray spectroscopic study of Po-212 was performed at the Grand Accelerateur National d'Ions Lourds, using the inverse kinematics alpha-transfer reaction C-12(Pb-208, Po-212) Be-8 and the AGATA spectrometer. A careful analysis based on gamma gamma coincidence relations allowed us to establish 14 new excited states in the energy range between 1.9 and 3.3 MeV. None of these states, however, can be considered as candidates for the levels with spins and parities of 1(-) and 2(-) and excitation energies below 2.1 MeV, which have been predicted by recent alpha-cluster model calculations. A systematic comparison of the experimentally established excitation scheme of Po-212 with shell-model calculations was performed. This comparison suggests that the six states with excitation energies (spins and parities) of 1744 (4(-)), 1751 (8(-)), 1787 (6(-)), 1946 (4(-)), 1986 (8(-)), and 2016 (6(-)) keV, which previously were interpreted as alpha-cluster states, may in fact be of positive parity and belong to low-lying shell-model multiplets. This reinterpretation of the structure of Po-212 is supported by experimental information with respect to the linear polarization of gamma rays, which suggests a magnetic character of the 432-keV gamma ray decaying from the state at an excitation energy of 1787 keV to the 6(1)(+) yrast state, and exclusive reaction cross sections.
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