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Molina, F. et al, Rubio, B., Agramunt, J., Algora, A., Domingo-Pardo, C., Gadea, A., et al. (2015). T-z =-1 -> 0 beta decays of Ni-54, Fe-50, Cr-46, and Ti-42 and comparison with mirror (He-3,t) measurements. Phys. Rev. C, 91(1), 014301–19pp.
Abstract: We have studied the beta decay of the T-z = -1, f(7/2) shell nuclei Ni-54, Fe-50, Cr-46, and Ti-42 produced in fragmentation reactions. The proton separation energies in the daughter T-z = 0 nuclei are relatively large (approximate to 4-5 MeV) so studies of the. rays are essential. The experiments were performed at GSI as part of the Stopped-beam campaign with the RISING setup consisting of 15 Euroball Cluster Ge detectors. From the newly obtained high precision beta-decay half-lives, excitation energies, and beta branching ratios, we were able to extract Fermi and Gamow-Teller transition strengths in these beta decays. With these improved results it was possible to compare in detail the Gamow-Teller (GT) transition strengths observed in beta decay including a sensitivity limit with the strengths of the T-z = +1 to T-z = 0 transitions derived from high resolution (He-3,t) reactions on the mirror target nuclei at RCNP, Osaka. The accumulated B(GT) strength obtained from both experiments looks very similar although the charge exchange reaction provides information on a broader energy range. Using the “merged analysis” one can obtain a full picture of the B(GT) over the full Q(beta) range. Looking at the individual transitions some differences are observed, especially for the weak transitions. Their possible origins are discussed.
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Molina, F., Aguilera, P., Romero-Barrientos, J., Arellano, H. F., Agramunt, J., Medel, J., et al. (2017). Energy distribution of the neutron flux measurements at the Chilean Reactor RECH-1 using multi-foil neutron activation and the Expectation Maximization unfolding algorithm. Appl. Radiat. Isot., 129, 28–34.
Abstract: We present a methodology to obtain the energy distribution of the neutron flux of an experimental nuclear reactor, using multi-foil activation measurements and the Expectation Maximization unfolding algorithm, which is presented as an alternative to well known unfolding methods such as GRAVEL. Self-shielding flux corrections for energy bin groups were obtained using MCNP6 Monte Carlo simulations. We have made studies at the at the Dry Tube of RECH-1 obtaining fluxes of 1.5(4) x 10(13) cm(-2) s(-1) for the thermal neutron energy region, 1.9(5) x 10(12) cm(-2) s(-1) for the epithermal neutron energy region, and 4.3(11) x 10(11) cm(-2) s(-1) for the fast neutron energy region.
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Morales, A. I. et al, Agramunt, J., Algora, A., Gadea, A., Molina, F., & Rubio, B. (2011). Synthesis of N=127 isotones through (p,n) charge-exchange reactions induced by relativistic (208)Pb projectiles. Phys. Rev. C, 84(1), 011601–5pp.
Abstract: The production cross sections of four N = 127 isotones ((207)Hg, (206)Au, (205)Pt, and (204)Ir) have been measured using (p,n) charge-exchange reactions, induced in collisions of a (208)Pb primary beam at 1 A GeV with a Be target. These data allow one to investigate the use of a reaction mechanism to extend the limits of the chart of nuclides toward the important r-process nuclei in the region of the third peak of elemental abundance distribution.
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Morales, A. I. et al, Algora, A., Rubio, B., Orrigo, S. E. A., Agramunt, J., Gelletly, W., et al. (2017). Simultaneous investigation of the T=1(J(pi)=0(+)) and T=0(J(pi)=9(+)) beta decays in Br-70. Phys. Rev. C, 95(6), 064327–11pp.
Abstract: The beta decay of the odd-odd nucleus Br-70 has been investigated with the BigRIPS and EURICA setups at the Radioactive Ion Beam Factory (RIBF) of the RIKEN Nishina Center. The T = 0(J(pi) = 9(+)) and T = 1(J(pi) = 0(+)) isomers have both been produced in in-flight fragmentation of Kr-78 with ratios of 41.6(8)% and 58.4(8)%, respectively. A half-life of t(1/2) = 2157(-49)(+53) ms has been measured for the J pi = 9(+) isomer from gamma-ray time decay analysis. Based on this result, we provide a new value of the half-life for the J pi = 0(+) ground state of Br-70, t(1/2) = 78.42 +/- 0.51 ms, which is slightly more precise, and in excellent agreement, with the best measurement reported hitherto in the literature. For this decay, we provide the first estimate of the total branching fraction decaying through the 2(1)(+) state in the daughter nucleus Se-70, R(2(1)(+)) = 1.3 +/- 1.1%. We also report four new low-intensity gamma-ray transitions at 661, 1103, 1561, and 1749 keV following the beta decay of the J pi = 9(+) isomer. Based on their coincidence relationships, we tentatively propose two new excited states at 3945 and 4752 keV in 70Se with most probable spins and parities of J(pi) = (6(+)) and (8(+)), respectively. The observed structure is interpreted with the help of shell-model calculations, which predict a complex interplay between oblate and prolate configurations at low excitation energies.
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Nacher, E., Rubio, B., Algora, A., Cano-Ott, D., Tain, J. L., Gadea, A., et al. (2016). Observations of the Gamow-Teller resonance in the rare-earth nuclei above Gd-146 populated in beta decay. Phys. Rev. C, 93(1), 014308–13pp.
Abstract: The rare-earth region of the nuclear table around the quasi-doubly magic nucleus Gd-146 is one of the very few places in which the Gamow-Teller (GT) resonance can be populated in beta decay. The appropriate technique to study such a phenomenon is total absorption spectroscopy, thanks to which one can measure the B(GT) distribution in beta-decay experiments even when it is very fragmented and lies at high excitation energy in the daughter nucleus. Results on the GT resonance measured in the beta decay of the odd-Z, N = 83 nuclei Tb-148, Ho-150, and Tm-152 are presented in this work and compared with shell-model calculations. The tail of the resonance is clearly observed up to the limit imposed by the Q value. This observation is important in the context of the understanding of the “quenching” of the GT strength.
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