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Fujita, Y., Rubio, B., Molina, F., Adachi, T., Fujita, H., Blank, B., et al. (2016). The Tz = ±1 → 0 and ±2 →±1 Mirror Gamow–Teller transitions in pf-shell nuclei. Acta Phys. Pol. B, 47(3), 867–881.
Abstract: Gamow-Teller (GT) transitions are the most common weak-interaction processes in the Universe. They play important roles in various processes of nucleosynthesis, for example, in the rapid proton-capture process (rp-process). In the pf-shell region, the rp-process runs through neutron-deficient nuclei with T-z = -2, -1, and 0 mainly by means of GT and Fermi transitions, where T-z is the z component of isospin T defined by T-z = (N = Z)/2. Under the assumption of isospin symmetry, mirror nuclei with reversed Z and N numbers, and thus with opposite signs of T-z, have the same structure. Therefore, symmetry is also expected for the GT transitions starting from and ending up in mirror nuclei. We have been studying the T-z = -2 -> -1 and -1 -> 0 GT transitions in beta decays, while those from stable T-z = +2 and +1 nuclei by means of hadronic (He-3; t) charge-exchange (CE) reactions. The results from these studies are compared in order to examine the mirror-symmetry structure in nuclei. In addition, these results are combined for the better understanding of GT transitions in the pf-shell region.
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Caballero-Folch, R. et al, Agramunt, J., Tain, J. L., Algora, A., Domingo-Pardo, C., Guadilla, V., et al. (2018). First determination of beta-delayed multiple neutron emission beyond A=100 through direct neutron measurement: The P-2n value of Sb-136. Phys. Rev. C, 98(3), 034310–10pp.
Abstract: Background: beta-delayed multiple neutron emission has been observed for some nuclei with A <= 100 being the Rb-100 the heaviest beta 2n emitter measured to date. So far only 25 P-2n values have been determined for the approximate to 300 nuclei that may decay in this way. Accordingly it is of interest to measure P-2n values for the other possible multiple neutron emitters throughout the chart of the nuclides. It is of particular interest to make such a measurement for nuclei with A > 100 to test the predictions of theoretical models and simulation tools for the decays of heavy nuclei in the region of very neutron-rich nuclei. In addition the decay properties of these nuclei are fundamental for the understanding of astrophysical nucleosynthesis processes such as the r-process and safety inputs for nuclear reactors. Purpose: To determine for the first time the two-neutron branching ratio the P-2n value for Sb-136 through a direct neutron measurement and to provide precise P-1n values for Sb-136 and Te-136. Method: A pure beam of each isotope of interest was provided by the JYFLTRAP Penning trap at the Ion Guide Isotope Separator On-Line (IGISOL) facility of the University of Jyvaskyla Finland. The purified ions were implanted into a moving tape at the end of the beam line. The detection setup consisted of a plastic scintillator placed right behind the implantation point after the tape to register the beta decays and the BELEN detector based on neutron counters embedded in a polyethylene matrix. The analysis was based on the study of the beta- and neutron-growth-and-decay curves and the beta-one-neutron and beta-two-neutron time correlations which allowed us the determination of the neutron branching ratios. Results: The P-2n value of Sb-136 was found to be 0.14(3)% and the measured P-1n values for Sb-136 and Te-136 were found to be 32.2(15)% and 1.47(6)% respectively. Conclusions: The measured P-2n value is a factor 44 smaller than predicted by the finite-range droplet model plus the quasiparticle random-phase approximation (FRDM+QRPA) model used for r-process calculations.
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Moreno, O., Sarriguren, P., Algora, A., Fraile, L. M., & Orrigo, S. E. A. (2022). Bulk and decay properties of neutron-deficient odd-mass Hg isotopes near A=185. Phys. Rev. C, 106(3), 034317–11pp.
Abstract: Ground and isomeric states of the neutron-deficient odd-A isotopes 183Hg, 185Hg, and 187Hg are described from a microscopic calculation based on a self-consistent, axially deformed Hartree-Fock mean field with the Skyrme functional and pairing within BCS approximation. For each equilibrium shape and different odd-neutron states, results on mean-square charge radii and magnetic dipole moments are given and analyzed in the context of their sensitivity to the nuclear deformation and to the spin and parity. Spin-isospin correlations within proton-neutron quasiparticle random phase approximation are then introduced in the nuclear states to obtain the distributions of Gamow-Teller strength and the beta+/EC half-lives of these isotopes, whose measurements are planned at ISOLDE-CERN using total absorption gamma-ray spectroscopy techniques.
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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.
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XENON Collaboration(Aprile, E. et al), & Orrigo, S. E. A. (2017). Search for two-neutrino double electron capture of Xe-124 with XENON100. Phys. Rev. C, 95(2), 024605–6pp.
Abstract: Two-neutrino double electron capture is a rare nuclear decay where two electrons are simultaneously captured from the atomic shell. For Xe-124 this process has not yet been observed and its detection would provide a new reference for nuclear matrix element calculations. We have conducted a search for two-neutrino double electron capture from the K shell of 124Xe using 7636 kg d of data from the XENON100 dark matter detector. Using a Bayesian analysis we observed no significant excess above background, leading to a lower 90% credibility limit on the half-life T-1/2 > 6.5 x 10(20) yr. We have also evaluated the sensitivity of the XENON1T experiment, which is currently being commissioned, and found a sensitivity of T-1/2 > 6.1 x 10(22) yr after an exposure of 2 t yr.
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