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Fujita, H. et al, Algora, A., Estevez-Aguado, E., Molina, F., & Rubio, B. (2019). Experimental study of Gamow-Teller transitions via the high-energy-resolution O-18(He-3, t)F-18 reaction: Identification of the low-energy “super” -Gamow-Teller state. Phys. Rev. C, 100(3), 034618–13pp.
Abstract: Using the high-resolution O-18(He-3, t)F-18 reaction at 0 degrees and at 140 MeV/nucleon, Gamow-Teller (GT) transitions were studied. A high energy resolution of 31 keV was achieved by applying dispersion matching techniques. The main part of the observed GT transition strength is concentrated in the transition to the F-18 ground state (g.s.). The absolute values of the reduced GT transition strengths, B(GT), were derived up to E-x = 12 MeV assuming proportionality between the B(GT) values and the reaction cross sections at 0 degrees. The B(GT) value obtained from the beta decay of F-18 (g.s.) -> O-18 (g.s.) was used to determine the proportionality constant. A total B(GT) of 4.06(5) was found and 76(1)% of the strength is concentrated to the ground state of F-18. The obtained B(GT) values were compared with those from the O-18(p, n) F-18 reaction and the mirror symmetric beta(+) decay of Ne-18 -> F-18. The candidates for 1(+) states with isospin T = 1 were identified by comparison with the O-18(p, p') data. The results of shell-model and quasiparticle-random-phase approximation calculations suggest constructive contributions of various configurations to the F-18 ground state, suggesting that this state is the low-energy super GT state.
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Romero-Barrientos, J., Marquez Damian, J. I., Molina, F., Zambra, M., Aguilera, P., Lopez-Usquiano, F., et al. (2022). Calculation of kinetic parameters beta eff and L with modified open source Monte Carlo code OpenMC(TD). Nucl. Eng. Technol., 54(3), 811–816.
Abstract: This work presents the methodology used to expand the capabilities of the Monte Carlo code OpenMC for the calculation of reactor kinetic parameters: effective delayed neutron fraction beff and neutron generation time L. The modified code, OpenMC(Time-Dependent) or OpenMC(TD), was then used to calculate the effective delayed neutron fraction by using the prompt method, while the neutron generation time was estimated using the pulsed method, fitting L to the decay of the neutron population. OpenMC(TD) is intended to serve as an alternative for the estimation of kinetic parameters when licensed codes are not available. The results obtained are compared to experimental data and MCNP calculated values for 18 benchmark configurations.
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Jordan, D. et al, Algora, A., Tain, J. L., Rubio, B., Agramunt, J., Perez-Cerdan, A. B., et al. (2013). Total absorption study of the beta decay of Tc-102,Tc-104,Tc-105. Phys. Rev. C, 87(4), 044318–14pp.
Abstract: The beta-feeding probabilities for three important contributors to the decay heat in nuclear reactors, namely Tc-102,Tc-104,Tc-105, have been measured using the total absorption spectroscopy technique. For the measurements, sources of very high isobaric purity have been obtained using a Penning trap (JYFLTRAP). A detailed description of the data analysis is given and the results are compared with high-resolution measurements and theoretical calculations. DOI: 10.1103/PhysRevC.87.044318
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Orrigo, S. E. A. et al, Rubio, B., Gelletly, W., Agramunt, J., Algora, A., & Molina, F. (2016). beta decay of the exotic T-z =-2 nuclei Fe-48, Ni-52, and Zn-56. Phys. Rev. C, 93(4), 044336–18pp.
Abstract: The results of a study of the beta decays of three proton-rich nuclei with T-z = -2, namely Fe-48, Ni-52, and Zn-56, produced in an experiment carried out at GANIL, are reported. In all three cases we have extracted the half-lives and the total beta-delayed proton emission branching ratios. We have measured the individual beta-delayed protons and beta-delayed. rays and the branching ratios of the corresponding levels. Decay schemes have been determined for the three nuclei, and new energy levels are identified in the daughter nuclei. Competition between beta-delayed protons and. rays is observed in the de-excitation of the T = 2 isobaric analog states in all three cases. Absolute Fermi and Gamow-Teller transition strengths have been determined. The mass excesses of the nuclei under study have been deduced. In addition, we discuss in detail the data analysis taking as a test case Zn-56, where the exotic beta-delayed gamma-proton decay has been observed.
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Orrigo, S. E. A. et al, Rubio, B., Gelletly, W., Agramunt, J., Algora, A., & Molina, F. (2016). Observation of the 2(+) isomer in Co-52. Phys. Rev. C, 94(4), 044315–8pp.
Abstract: We report the first observation of the 2(+) isomer in Co-52, produced in the beta decay of the 0(+), Ni-52 ground state. We have observed three. rays at 849, 1910, and 5185 keV characterizing the beta de-excitation of the isomer. We have measured a half-life of 102(6) ms for the isomeric state. The Fermi and Gamow-Teller transition strengths for the beta decay of Co-52m to Fe-52 have been determined. We also add new information on the beta decay of the 6(+), Co-52 ground state, for which we have measured a half-life of 112(3) ms.
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Denis Bacelar, A. M. et al, Algora, A., Molina, F., & Rubio, B. (2013). The population of metastable states as a probe of relativistic-energy fragmentation reactions. Phys. Lett. B, 723(4-5), 302–306.
Abstract: Isomeric ratios have been measured for high-spin states in Po-198,200,206,208(84), At-208,209,210,211(85), Rn-210,211,212,213,214(86), Fr-208,211,212,213,214(87), Ra-210,211,212,214,215(88), and Ac-215(89) following the projectile fragmentation of a 1 AGeV U-238 beam by a Be-9 target at GSI Helmholtzzentrum fur Schwerionenforschung. The fragments were separated in the fragment separator (FRS) and identified by means of energy loss and time-of-flight techniques. They were brought to rest at the centre of the RISING gamma-ray detector array and intensities of gamma rays emitted in the decay of isomeric states with half-lives between 100 ns and 40 μs and spin values up to 55/2 (h) over bar were used to obtain the corresponding isomeric ratios. The data are compared to theoretical isomeric ratios calculated in the framework of the abrasion-ablation model. Large experimental enhancements are obtained for high-spin isomers in comparison to expected values.
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Perez-Cerdan, A. B., Rubio, B., Gelletly, W., Algora, A., Agramunt, J., Burkard, K., et al. (2011). beta decay of (78)Sr. Phys. Rev. C, 84(5), 054311–15pp.
Abstract: The gamma rays and conversion electrons emitted in the beta decay of (78)Sr to levels in (78)Rb have been studied using Ge detectors and a mini-orange spectrometer. A reliable level scheme based on the results of these experiments has been established. The properties of the levels in (78)Rb have been compared with calculations based on deformed Hartree-Fock with Skyrme interactions and pairing correlations in the BCS approximation. This has allowed an interpretation of the nature of the observed sets of levels in the odd-odd nucleus (78)Rb.
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Guess, C. J. et al, Algora, A., Estevez, E., Molina, F., & Rubio, B. (2011). The Nd-150(He-3,t) and Sm-150(t,He-3) reactions with applications to beta beta decay of Nd-150. Phys. Rev. C, 83(6), 064318–17pp.
Abstract: The Nd-150(3He,t) reaction at 140 MeV/u and Sm-150(t,He-3) reaction at 115 MeV/u were measured, populating excited states in Pm-150. The transitions studied populate intermediate states of importance for the (neutrinoless) beta beta decay of Nd-150 to Sm-150. Monopole and dipole contributions to the measured excitation-energy spectra were extracted by using multipole decomposition analyses. The experimental results were compared with theoretical calculations obtained within the framework of the quasiparticle random-phase approximation, which is one of the main methods employed for estimating the half-life of the neutrinoless beta beta decay (0 nu beta beta) of Nd-150. The present results thus provide useful information on the neutrino responses for evaluating the 0 nu beta beta and 2 nu beta beta matrix elements. The 2 nu beta beta matrix element calculated from the Gamow-Teller transitions through the lowest 1(+) state in the intermediate nucleus is maximally about half that deduced from the half-life measured in 2 nu beta beta direct counting experiments, and at least several transitions through 1+ intermediate states in Pm-150 are required to explain the 2 nu beta beta half-life. Because Gamow-Teller transitions in the Sm-150(t,3He) experiment are strongly Pauli blocked, the extraction of Gamow-Teller strengths was complicated by the excitation of the 2 (h) over bar omega, Lambda L = 0, Delta S = 1 isovector spin-flip giant monopole resonance (IVSGMR). However, the near absence of Gamow-Teller transition strength made it possible to cleanly identify this resonance, and the strength observed is consistent with the full exhaustion of the non-energy-weighted sum rule for the IVSGMR.
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Karakoc, M. et al, & Molina, F. (2014). Gamow-Teller transitions in the A=40 isoquintet of relevance for neutrino captures in Ar-40. Phys. Rev. C, 89(6), 064313–7pp.
Abstract: Background: The Gamow-Teller response of Ar-40 is important for the use of liquid argon as a medium for neutrino detection. An ambiguity about the Gamow-Teller strength for the excitation of 1(+) states at 2290 and 2730 keV in K-40 results in a significant uncertainty for neutrino capture rates. This ambiguity is caused by the large discrepancy observed between strengths extracted from Ar-40(p, n) charge-exchange data and the transition strengths for the analog transitions studied in the beta decay of Ti-40. Purpose: This study was aimed at resolving the ambiguity between the results from the Ar-40(p, n) charge-exchange and Ti-40 beta-decay data. Method: Shell-model calculations in the sd-pf shell with a new interaction (WBMB-C) were used to study differences between the structure of the transitions from Ar-40 and Ti-40. Distorted-wave Born approximation reaction calculations were used to investigate uncertainties in the extraction of Gamow-Teller strength from the Ar-40(p, n) data. New high-resolution data for the Ar-40(He-3,t) reaction were used to gain further insight into the charge-exchange reaction mechanism and to provide more information to test the validity of the shell-model calculations. Results: The shell-model calculations showed that interference between amplitudes associated with pf and sd components to the low-lying Gamow-Teller transitions, in combination with a difference in Coulomb energy shifts for Ar-40 and Ti-40, can produce the differences on the scale of those observed between the Ar-40 charge-exchange and Ti-40 beta-decay data. In combination with the difference in nuclear penetrability of the (p, n) and (He-3,t) probes, the different contributions from amplitudes associated with transitions in the pf and sd shells are likely also responsible for the observed discrepancy between the ratio of the cross sections for the low-lying 1(+) states in the Ar-40(p, n) and Ar-40(He-3,t) data. Conclusions: On the basis of this study, it is recommended to use Gamow-Teller strengths extracted from the Ar-40(p, n) data, not the Ti-40 beta-decay data, for the calculation of neutrino capture rates. Further theoretical studies are required to achieve a consistent quantitative description for the energy differences between low-lying 1(+) states in K-40 and Sc-40 and the experimentally observed Gamow-Teller strengths.
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Ganioglu, E. et al, Rubio, B., Algora, A., Estevez-Aguado, E., & Molina, F. (2016). High-resolution study of Gamow-Teller transitions in the Ti-48(He-3,t)V-48 reaction. Phys. Rev. C, 93(6), 064326–10pp.
Abstract: In this work we have studied T-z = +2 -> +1, Gamow-Teller (GT) transitions in the Ti-48(He-3, t)V-48 chargeexchange reaction at 140 MeV/nucleon and 0 degrees at the Research Center for Nuclear Physics, Osaka. From the high-resolution facility, consisting of a high-dispersion beamline and the Grand Raiden spectrometer, the spectrum had an energy resolution of 21 keV, among the best achieved. Individual GT transitions were observed and GT strength was derived for each state populated up to an excitation energy of 12 MeV. The total sum of the B(GT) strength observed in discrete states was 4.0, which is 33% of the sum-rule-limit value of 12. The results were compared with the results of shell-model calculations carried out with the GXPF1J interaction. The measured B(GT) distribution was also compared with that obtained in the (He-3, t) charge-exchange reaction on Ti-47. On the assumption of isospin symmetry the beta spectrum of the T-z = -2 nucleus Fe-48 was deduced from the observed spectrum in the Ti-48(He-3, t)V-48 reaction and this predicted spectrum was compared with the measured one.
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