Jungclaus, A. et al, Gadea, A., & Montaner-Piza, A. (2016). First observation of gamma rays emitted from excited states south-east of Sn-132: The pi g(9/2)(-1) circle times nu f(7/2) multiplet of In-132(83). Phys. Rev. C, 93(4), 041301–6pp.
Abstract: For the first time, the gamma decay of excited states has been observed in a nucleus situated in the quadrant south-east of doubly magic Sn-132, a region in which experimental information so far is limited to ground-state properties. Six gamma rays with energies of 50, 86, 103, 227, 357, and 602 keV were observed following the beta-delayed neutron emission from Cd-133(85), populated in the projectile fission of a U-238 beam at the Radioactive Isotope Beam Factory at RIKEN within the EURICA project. The new experimental information is compared to the results of a modern realistic shell-model calculation, the first one in this region very far from stability, focusing in particular on the pi 0g(9/2)(-1) circle times nu 1f(7/2) particle-hole multiplet in In-132(83). In addition, theoretical estimates based on a scaling of the two-body matrix elements for the pi h(11/2)(-1) circle times nu g(9/2) analog multiplet in Tl-208(127), one major proton and one major neutron shell above, are presented.
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Blank, B. et al, Agramunt, J., Algora, A., Guadilla, V., Montaner-Piza, A., Morales, A. I., et al. (2016). New neutron-deficient isotopes from Kr-78 fragmentation. Phys. Rev. C, 93(6), 061301–5pp.
Abstract: In an experiment with the RIKEN projectile fragment separator called BigRIPS at the RIKEN Nishina Center, the fragmentation of a Kr-78 beam allowed the observation of new neutron-deficient isotopes at the proton drip line. Clean identification spectra could be produced and Se-63, Kr-67, and Kr-68 were identified for the first time. In addition, Ge-59 was also observed. Three of these isotopes, Ge-59, Se-63, and Kr-67, are potential candidates for ground-state two-proton radioactivity. In addition, the isotopes Ge-58, Se-62, and Kr-66 were also sought but without success. The present experiment also allowed the determination of production cross sections for some of the most exotic isotopes. These measurements confirm the trend already observed that the empirical parametrization of fragmentation cross sections, EPAX, significantly overestimates experimental cross sections in this mass region.
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Jungclaus, A. et al, Gadea, A., & Montaner-Piza, A. (2016). beta decay of semi-magic Cd-130: Revision and extension of the level scheme of In-130. Phys. Rev. C, 94(2), 024303–8pp.
Abstract: The beta decay of the semi-magic nucleus Cd-130 has been studied at the RIBF facility at the RIKEN Nishina Center. The high statistics of the present experiment allowed for a revision of the established level scheme of In-130 and the observation of additional beta feeding to high- lying core-excited states in In-130. The experimental results are compared to shell-model calculations employing a model space consisting of the full major N = 50-82 neutron and Z = 28-50 proton shells and the NA-14 interaction, and good agreement is found.
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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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Guadilla, V. et al, Algora, A., Tain, J. L., Agramunt, J., Jordan, M. D., Montaner-Piza, A., et al. (2017). Experimental study of Tc-100 beta decay with total absorption gamma-ray spectroscopy. Phys. Rev. C, 96(1), 014319–10pp.
Abstract: The beta decay of Tc-100 has been studied by using the total absorption gamma-ray spectroscopy technique at the Ion Guide Isotope Separator On-Line facility in Jyvaskyla. In this work the new Decay Total Absorption gamma-ray Spectrometer in coincidence with a cylindrical plastic beta detector has been employed. The beta intensity to the ground state obtained from the analysis is in good agreement with previous high-resolution measurements. However, differences in the feeding to the first-excited state as well as weak feeding to a new level at high excitation energy have been deduced from this experiment. Theoretical calculations performed in the quasiparticle random-phase approximation framework are also reported. Comparison of these calculations with our measurement serves as a benchmark for calculations of the double beta decay of Mo-100.
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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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Guadilla, V., Algora, A., Tain, J. L., Agramunt, J., Jordan, D., Monserrate, M., et al. (2019). Total absorption gamma-ray spectroscopy of niobium isomers. Phys. Rev. C, 100(2), 024311–15pp.
Abstract: The beta-intensity distributions of the decays of Nb-100gs,Nb-100m and Nb-102gs,Nb-102m have been determined using the total absorption gamma-ray spectroscopy technique. The JYFLTRAP double Penning trap system was employed in a campaign of challenging measurements performed with the decay total absorption gamma-ray spectrometer at the Ion Guide Isotope Separator On-Line facility in Jyvaskyla. Different strategies were applied to disentangle the isomeric states involved, lying very close in energy. The low-spin component of each niobium case was populated through the decay of the zirconium parent, which was treated as a contaminant. We have applied a method to extract this contamination, and additionally we have obtained beta-intensity distributions for these zirconium decays. The beta-strength distributions evaluated with these results were compared with calculations in a quasiparticle random-phase approximation, suggesting a prolate configuration for the ground states of Zr-100,Zr-102. The footprint of the Pandemonium effect was found when comparing our results for the analyses of the niobium isotopes with previous decay data. The beta-intensities of the decay of Nb-102m, for which there were no previous data, were obtained. A careful evaluation of the uncertainties was carried out, and the consistency of our results was validated taking advantage of the segmentation of our spectrometer. The final results were used as input in reactor summation calculations. A large impact on antineutrino spectrum calculations was already reported, and here we detail the significant impact on decay heat calculations.
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Guadilla, V. et al, Tain, J. L., Algora, A., Agramunt, J., Jordan, D., Monserrate, M., et al. (2019). Total absorption gamma-ray spectroscopy of the beta-delayed neutron emitters I-137 and Rb-95. Phys. Rev. C, 100(4), 044305–17pp.
Abstract: The decays of the beta-delayed neutron emitters( 137)I and Rb-95 have been studied with the total absorption gamma-ray spectroscopy technique. The purity of the beams provided by the JYFLTRAP Penning trap at the ion guide isotope separator on-line facility in Jyvaskyla allowed us to carry out a campaign of isotopically pure measurements with the decay total absorption gamma-ray spectrometer, a segmented detector composed of 18 NaI(T1) modules. The contamination coming from the interaction of neutrons with the spectrometer has been carefully studied, and we have tested the use of time differences between prompt gamma rays and delayed neutron interactions to eliminate this source of contamination. Due to the sensitivity of our spectrometer, we have found a significant amount of beta intensity to states above the neutron separation energy that deexcite by gamma rays, comparable to the neutron emission probability. The competition between gamma deexcitation and neutron emission has been compared with Hauser-Feshbach calculations, and it can be understood as a nuclear structure effect. In addition, we have studied the impact of the beta-intensity distributions determined in this work on reactor decay heat and reactor antineutrino spectrum summation calculations. The robustness of our results is demonstrated by a thorough study of uncertainties and with the reproduction of the spectra of the individual modules and the module-multiplicity gated spectra. This work represents the state-of-the-art of our analysis methodology for segmented total absorption spectrometers.
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Jungclaus, A. et al, & Montaner-Piza, A. (2020). Evolution of proton single-particle states in neutron-rich Sb isotopes beyond N=82. Phys. Rev. C, 102(3), 034324–11pp.
Abstract: The beta decay of the semimagic Sn isotopes Sn-136,Sn-137,Sn-138 has been studied at the Radioactive Isotope Beam Factory at the RIKEN Nishina Center. The first experimental information on excited states was obtained for Sb-137 while, in the case of Sb-136, the established excitation scheme could be extended by ten previously unidentified levels. In the decay of the most-neutron-rich isotope Sn-138, two gamma rays were observed for the first time. The new experimental results, in combination with state-of-the-art shell-model calculations, provide the first information with respect to the evolution of the Og(7/2) and 1d(5/2) proton single-particle states with increasing neutron number beyond N = 84.
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Guadilla, V. et al, Tain, J. L., Algora, A., Agramunt, J., Jordan, D., Monserrate, M., et al. (2020). Determination of beta-decay ground state feeding of nuclei of importance for reactor applications. Phys. Rev. C, 102(6), 064304–12pp.
Abstract: In beta-decay studies the determination of the decay probability to the ground state (g.s.) of the daughter nucleus often suffers from large systematic errors. The difficulty of the measurement is related to the absence of associated delayed gamma-ray emission. In this work we revisit the 4 pi gamma – beta method proposed by Greenwood and collaborators in the 1990s, which has the potential to overcome some of the experimental difficulties. Our interest is driven by the need to determine accurately the beta-intensity distributions of fission products that contribute significantly to the reactor decay heat and to the antineutrinos emitted by reactors. A number of such decays have large g.s. branches. The method is relevant for nuclear structure studies as well. Pertinent formulas are revised and extended to the special case of beta-delayed neutron emitters, and the robustness of the method is demonstrated with synthetic data. We apply it to a number of measured decays that serve as test cases and discuss the features of the method. Finally, we obtain g.s. feeding intensities with reduced uncertainty for four relevant decays that will allow future improvements in antineutrino spectrum and decay heat calculations using the summation method.
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