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Mistry, A. K. et al, Tain, J. L., Agramunt, J., Algora, A., Guadilla, V., Morales, A. I., et al. (2022). The DESPEC setup for GSI and FAIR. Nucl. Instrum. Methods Phys. Res. A, 1033, 166662–18pp.
Abstract: The DEcay SPECtroscopy (DESPEC) setup for nuclear structure investigations was developed and commissioned at GSI, Germany in preparation for a full campaign of experiments at the FRS and Super-FRS. In this paper, we report on the first employment of the setup in the hybrid configuration with the AIDA implanter coupled to the FATIMA LaBr3(Ce) fast-timing array, and high-purity germanium detectors. Initial results are shown from the first experiments carried out with the setup. An overview of the setup and function is discussed, including technical advancements along the path.
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Goigoux, T. et al, Algora, A., Guadilla, V., Montaner-Piza, A., Morales, A. I., Orrigo, S. E. A., et al. (2016). Two-Proton Radioactivity of Kr-67. Phys. Rev. Lett., 117(16), 162501–6pp.
Abstract: In an experiment with the BigRIPS separator at the RIKEN Nishina Center, we observed two-proton (2p) emission from Kr-67. At the same time, no evidence for 2p emission of Ge-59 and Se-63, two other potential candidates for this exotic radioactivity, could be observed. This observation is in line with Q value predictions which pointed to Kr-67 as being the best new candidate among the three for two-proton radioactivity. Kr-67 is only the fourth 2p ground-state emitter to be observed with a half-life of the order of a few milliseconds. The decay energy was determined to be 1690(17) keV, the 2p emission branching ratio is 37(14)%, and the half-life of Kr-67 is 7.4(30) ms.
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Morales, A. I. et al. (2017). Type II shell evolution in A=70 isobars from the N >= 40 island of inversion. Phys. Lett. B, 765, 328–333.
Abstract: The level structures of Co-70 and Ni-70, populated from the Chi decay of Fe-70, have been investigated using beta-delayed gamma-ray spectroscopy following in-flight fission of a U-238 beam. The experimental results are compared to Monte-Carlo Shell-Model calculations including the pf + g(9/2) + d(5/2) orbitals. The strong population of a (1(+)) state at 274 keV in Co-70 is at variance with the expected excitation energy of 1 MeV from near spherical single-particle estimates. This observation indicates a dominance of prolate deformed intruder configurations in the low-lying levels, which coexist with the normal near spherical states. It is shown that the 13 decay of the neutron-rich A = 70 isobars from the new island of inversion to the Z = 28 closed-shell regime progresses in accordance with a newly reported type of shell evolution, the so-called Type II, which involves many particle-hole excitations across energy gaps.
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Yokoyama, R. et al, Tain, J. L., Algora, A., Agramunt, J., Domingo-Pardo, C., Morales, A. I., et al. (2023). β-delayed neutron emissions from N > 50 gallium isotopes. Phys. Rev. C, 108(6), 064307–15pp.
Abstract: beta-delayed gamma-neutron spectroscopy has been performed on the decay of A=84 to 87 gallium isotopes at the RI-beam Factory at the RIKEN Nishina Center using a high-efficiency array of 3He neutron counters (BRIKEN). beta-2n-gamma events were measured in the decays of all of the four isotopes for the first time, which is direct evidence for populating the excited states of two-neutron daughter nuclei. Detailed decay schemes with the gamma branching ratios were obtained for these isotopes, and the neutron emission probabilities (P-xn) were updated from the previous study. Hauser-Feshbach statistical model calculations were performed to understand the experimental branching ratios. We found that the P-1n and P-2n values are sensitive to the nuclear level densities of 1n daughter nuclei and showed that the statistical model reproduced the P-2n/P-1n ratio better when experimental levels plus shell-model level densities fit by the Gilbert-Cameron formula were used as the level-density input. We also showed the neutron and gamma branching ratios are sensitive to the ground-state spin of the parent nucleus. Our statistical model analysis suggested J <= 3 for the unknown ground-state spin of the odd-odd nucleus Ga-86, from the I gamma(4(+)-> 2(+))/I-gamma(2(+)-> 0(+)) ratio of Ga-84 and the P-2n/P-1n ratio. These results show the necessity of detailed understanding of the decay scheme, including data from neutron spectroscopy, in addition to gamma measurements of the multineutron emitters.
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