Perez-Vidal, R. M. et al, Gadea, A., Jurado, M., Domingo-Pardo, C., & Huyuk, T. (2022). Evidence of Partial Seniority Conservation in the pi g9/2 Shell for the N=50 Isotones. Phys. Rev. Lett., 129(11), 112501–7pp.
Abstract: The reduced transition probabilities for the 4+1 -2+1 and 2+1 -0+1 transitions in 92Mo and 94Ru and for the 4+1 -2+1 and 6+1 -4+1 transitions in 90Zr have been determined in this experiment making use of a multinucleon transfer reaction. These results have been interpreted on the basis of realistic shell-model calculations in the f5=2, p3=2, p1=2, and g9=2 proton valence space. Only the combination of extensive lifetime information and large scale shell-model calculations allowed the extent of the seniority conservation in the N = 50 g9=2 orbital to be understood. The conclusion is that seniority is largely conserved in the first 71g9=2 orbital.
|
Orrigo, S. E. A. et al, Rubio, B., Agramunt, J., Algora, A., & Molina, F. (2014). Observation of the beta-Delayed gamma-Proton Decay of Zn-56 and its Impact on the Gamow-Teller Strength Evaluation. Phys. Rev. Lett., 112(22), 222501–5pp.
Abstract: We report the observation of a very exotic decay mode at the proton drip line, the beta-delayed gamma-proton decay, clearly seen in the beta decay of the T-z = -2 nucleus Zn-56. Three gamma-proton sequences have been observed after the beta decay. Here this decay mode, already observed in the sd shell, is seen for the first time in the f p shell. Both. and proton decays have been taken into account in the estimation of the Fermi and Gamow-Teller strengths. Evidence for fragmentation of the Fermi strength due to strong isospin mixing is found.
|
n_TOF Collaboration(Lederer, C. et al), Domingo-Pardo, C., Giubrone, G., & Tain, J. L. (2013). Neutron Capture Cross Section of Unstable Ni-63: Implications for Stellar Nucleosynthesis. Phys. Rev. Lett., 110(2), 022501–5pp.
Abstract: The Ni-63(n, gamma) cross section has been measured for the first time at the neutron time-of-flight facility n_TOF at CERN from thermal neutron energies up to 200 keV. In total, capture kernels of 12 (new) resonances were determined. Maxwellian averaged cross sections were calculated for thermal energies from kT = 5-100 keV with uncertainties around 20%. Stellar model calculations for a 25M(circle dot) star show that the new data have a significant effect on the s-process production of Cu-63, Ni-64, and Zn-64 in massive stars, allowing stronger constraints on the Cu yields from explosive nucleosynthesis in the subsequent supernova.
|
n_TOF Collaboration(Guerrero, C. et al), Domingo-Pardo, C., & Tain, J. L. (2020). Neutron Capture on the s-Process Branching Point Tm-171 via Time-of-Flight and Activation. Phys. Rev. Lett., 125(14), 142701–8pp.
Abstract: The neutron capture cross sections of several unstable nuclides acting as branching points in the s process are crucial for stellar nucleosynthesis studies. The unstable Tm-171 (t(1/2) = 1.92 yr) is part of the branching around mass A similar to 170 but its neutron capture cross section as a function of the neutron energy is not known to date. In this work, following the production for the first time of more than 5 mg of Tm-171 at the high-flux reactor Institut Laue-Langevin in France, a sample was produced at the Paul Scherrer Institute in Switzerland. Two complementary experiments were carried out at the neutron time-of-flight facility (nTOF) at CERN in Switzerland and at the SARAF liquid lithium target facility at Soreq Nuclear Research Center in Israel by time of flight and activation, respectively. The result of the time -of-flight experiment consists of the first ever set of resonance parameters and the corresponding average resonance parameters, allowing us to make an estimation of the Maxwellian-averaged cross sections (MACS) by extrapolation. The activation measurement provides a direct and more precise measurement of the MACS at 30 keV: 384 (40) mb, with which the estimation from the nTOF data agree at the limit of 1 standard deviation. This value is 2.6 times lower than the JEFF-3.3 and ENDF/B-VIII evaluations, 25% lower than that of the Bao et al. compilation, and 1.6 times larger than the value recommended in the KAlloNiS (v1) database, based on the only previous experiment. Our result affects the nucleosynthesis at the A similar to 170 branching, namely, the Yb-171 abundance increases in the material lost by asymptotic giant branch stars, providing a better match to the available pre-solar SiC grain measurements compared to the calculations based on the current JEFF-3.3 model-based evaluation.
|
n_TOF Collaboration(Damone, L. et al), Domingo-Pardo, C., Tain, J. L., & Tarifeño-Saldivia, A. (2018). Be-7 (n,p)Li-7 Reaction and the Cosmological Lithium Problem: Measurement of the Cross Section in a Wide Energy Range at n_TOF at CERN. Phys. Rev. Lett., 121(4), 042701–7pp.
Abstract: We report on the measurement of the Be-7(n,p)Li-7 cross section from thermal to approximately 325 keV neutron energy, performed in the high-flux experimental area (EAR2) of the n_TOF facility at CERN. This reaction plays a key role in the lithium yield of the big bang nucleosynthesis (BBN) for standard cosmology. The only two previous time-of-flight measurements performed on this reaction did not cover the energy window of interest for BBN, and they showed a large discrepancy between each other. The measurement was performed with a Si telescope and a high-purity sample produced by implantation of a Be-7 ion beam at the ISOLDE facility at CERN. While a significantly higher cross section is found at low energy, relative to current evaluations, in the region of BBN interest, the present results are consistent with the values inferred from the time-reversal Li-7(p,n)Be-7 reaction, thus yielding only a relatively minor improvement on the so-called cosmological lithium problem. The relevance of these results on the near-threshold neutron production in the p + Li-7 reaction is also discussed.
|
