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Wrede, C., Sjue, S. K. L., Garcia, A., Swanson, H. E., Ahmad, I., Algora, A., et al. (2013). Electron capture on In-116 and implications for nuclear structure related to double-beta decay. Phys. Rev. C, 87(3), 031303–5pp.
Abstract: The electron capture decay branch of In-116 has been measured to be [2.46 +/- 0.44(stat.) +/- 0.39(syst.)] x 10(-4) using Penning trap-assisted decay spectroscopy. The corresponding Gamow-Teller transition strength is shown to be compatible with the most recent value extracted from the (p, n) charge-exchange reaction, providing a resolution to longstanding discrepancies. This transition can now be used as a reliable benchmark for nuclear-structure calculations of the matrix element for the neutrinoless double-beta decay of Cd-116 and other nuclides.
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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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Fujita, Y. et al, Algora, A., Estevez-Aguado, E., Molina, F., & Rubio, B. (2013). High-resolution study of T-z =+2 ->+1 Gamow-Teller transitions in the Ca-44(3He,t)Sc-44 reaction. Phys. Rev. C, 88(1), 014308–18pp.
Abstract: In order to study the Gamow-Teller (GT) transitions from the T-z = +2 nucleus Ca-44 to the T-z = +1 nucleus Sc-44, where T-z is the z component of isospin T, we performed the (p, n)-type (He-3, t) charge-exchange (CE) reaction at 140 MeV/nucleon and the scattering angles 0 degrees and 2.5 degrees. An energy resolution of 28 keV, that was realized by applying matching techniques to the magnetic spectrometer system, allowed the study of fragmented states. The GT transition strengths, B(GT), were derived up to the excitation energy (E-x) of 13.7 MeV assuming the proportionality between cross sections and B(GT) values. The total sum of B(GT) values in discrete states was 3.7, which was 31% of the sum-rule-limit value of 12. Shell model calculations using the GXPF1J interaction could reproduce the gross features of the experimental B(GT) distribution, but not the fragmentation of the strength. By introducing the concepts of isospin, properties of isospin analogous transitions and states were investigated. (i) Assuming isospin symmetry, the T-z = +2 -> +1 and T-z = -2 -> -1 mirror GT transitions should have the same properties, where the latter can be studied in the beta decay of Cr-44 to V-44. First, we confirmed that the beta-decay half-life T-1/2 of Cr-44 can be reproduced using the B(GT) distribution from the Ca-44(He-3, t) measurement. Then, the 0 degrees, (3He, t) spectrum was modified to deduce the “beta-decay spectrum” and it was compared with the delayed-proton spectrum from the Cr-44 beta decay. The two spectra were mostly in agreement for the GT excitations, but suppression of the proton decay was found for the T = 2 isobaric analog state (IAS). (ii) Starting from the T = 2 ground state of 44Ca, the (3He, t) can excite GT states (state populated by GT transitions) with T = 1, 2, and 3. On the other hand, the Ca-44(p, p') reaction can excite spin-M1 states (states populated by spin-M1 transitions) with T = 2 and 3 that are analogous to the T = 2 and 3 GT states, respectively. By comparing the spectra from these two reactions, a T value of 2 is suggested for several GT states in the E-x = 11.5-13.7 MeV region. (iii) It has been suggested that the T = 2, J(pi) = 0(+) double isobaric analog state (DIAS) at 9.338 MeV in the T-z = 0 nucleus Ti-44 forms an isospin-mixed doublet with a subsidiary 0(+) state at 9.298 MeV. Since no corresponding state was found in the T-z = +1 nucleus Sc-44, we suggest T = 0 for the subsidiary state.
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Perez-Cerdan, A. B., Rubio, B., Gelletly, W., Algora, A., Agramunt, J., Nacher, E., et al. (2013). Deformation of Sr and Rb isotopes close to the N = Z line via beta-decay studies using the total absorption technique. Phys. Rev. C, 88(1), 014324–15pp.
Abstract: A study of the Gamow-Teller strength distributions B(GT) in the beta decay of Sr-78 and Rb-76,Rb-78 has been made using a total absorption spectrometer (TAS). Following the success in deducing the sign of the deformation for Sr-76, a similar approach is adopted for Sr-78 based on a comparison of the measured B(GT) with quasiparticle random-phase approximation calculations. This work confirms its previously expected prolate deformation in the ground state. Conclusions about the structure of the odd-odd Rb-76,Rb-78 isotopes have been drawn based on their measured B(GT) distributions.
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Morales, A. I. et al, Algora, A., Molina, F., & Rubio, B. (2013). beta-delayed gamma-ray spectroscopy of Au-203,Au-204 and Pt200-202. Phys. Rev. C, 88(1), 014319–12pp.
Abstract: The beta decay of five heavy, neutron-rich nuclei, Pt-203,Pt-204 and Ir200-202, has been investigated following relativistic cold fragmentation reactions of lead projectiles using the FRS + RISING setup at GSI. This paper reports on the study of the low-lying states in the decay daughter nuclei Au-203,Au-204 and Pt200-202. The characteristic gamma rays for each nucleus have been determined using beta-delayed gamma-ray spectroscopy. Tentative level schemes, relative intensities, and apparent beta feedings are provided. These data are compared with shell-model calculations, which indicate a substantial contribution to the total beta strength from high-energy first-forbidden beta-decay transitions in this mass region.
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Mason, P. J. R. et al, & Algora, A. (2013). Half-life of the yrast 2(+) state in W-188: Evolution of deformation and collectivity in neutron-rich tungsten isotopes. Phys. Rev. C, 88(4), 044301–6pp.
Abstract: The half-life of the yrast I-pi = 2(+) state in the neutron-rich nucleus W-188 has been measured using fast-timing techniques with the HPGe and LaBr3:Ce array at the National Institute of Physics and Nuclear Engineering, Bucharest. The resulting value of t(1/2) = 0.87(12) ns is equivalent to a reduced transition probability of B(E2;2(1)(+) -> 0(1)(+)) = 85(12) W.u. for this transition. The B(E2;2(1)(+) -> 0(1)(+)) is compared to neighboring tungsten isotopes and nuclei in the Hf, Os, and Pt isotopic chains. Woods-Saxon potential energy surface (PES) calculations have been performed for nuclei in the tungsten isotopic chain and predict prolate deformed minima with rapidly increasing gamma softness for W184-192 and an oblate minimum for W-194.
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AGATA Collaboration(Modamio, V. et al), Gadea, A., Algora, A., & Huyuk, T. (2013). Lifetime measurements in neutron-rich Co-63,Co-65 isotopes using the AGATA demonstrator. Phys. Rev. C, 88(4), 044326–6pp.
Abstract: Lifetimes of the low-lying (11/2(-)) states in Co-63,Co-65 have been measured employing the recoil distance doppler shift method (RDDS) with the AGATA gamma-ray array and the PRISMA mass spectrometer. These nuclei were populated via a multinucleon transfer reaction by bombarding a U-238 target with a beam of Ni-64. The experimental B(E2) reduced transition probabilities for Co-63,Co-65 are well reproduced by large-scale shell-model calculations that predict a constant trend of the B(E2) values up to the N = 40 Co-67 isotope.
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Stanja, J. et al, Agramunt, J., & Algora, A. (2013). Mass spectrometry and decay spectroscopy of isomers across the Z=82 shell closure. Phys. Rev. C, 88(5), 054304–7pp.
Abstract: Recent results from a measurement campaign studying the isomerism in neutron-deficient Tl isotopes are presented. The measurements make use of a nuclear spectroscopy setup coupled to the high-resolution Penningtrap mass spectrometer ISOLTRAP at CERN's radioactive ion-beam facility ISOLDE. The mass values of Tl-190,Tl-194 are improved and a mass-spin-state assignment is carried out. An additional mass measurement of the grandparent nuclide At-198 allows the deduction of the spin-state ordering in Tl-190. As a result, the excitation energies of the isomers in both Tl isotopes are determined for the first time to Eex(Tl-194) = 260(15) keV and E-ex(Tl-190) = 89(12) keV. Furthermore, this allows anchoring of the ground-state and isomer masses of Bi-194, Fr-202, and Ac-206, which are linked by two independent a-decay chains.
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Morales, A. I. et al, Gadea, A., & Algora, A. (2014). beta-decay studies of neutron-rich Tl, Pb, and Bi isotopes. Phys. Rev. C, 89(1), 014324–13pp.
Abstract: The fragmentation of relativistic uranium projectiles has been exploited at the Gesellschaft fur Schwerionenforschung laboratory to investigate the beta decay of neutron-rich nuclei just beyond Pb-208. This paper reports on beta-delayed gamma decays of Tl211-213, Pb-215, and Bi215-219 de-exciting states in the daughters Pb211-213, Bi-215, and Po215-219. The resulting partial level schemes, proposed with the help of systematics and shell-model calculations, are presented. The role of allowed Gamow-Teller and first-forbidden beta transitions in this mass region is discussed.
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Sarriguren, P., Algora, A., & Pereira, J. (2014). Gamow-Teller response in deformed even and odd neutron-rich Zr and Mo isotopes. Phys. Rev. C, 89(3), 034311–13pp.
Abstract: beta-decay properties of neutron-rich Zr and Mo isotopes are investigated within a microscopic theoretical approach based on the proton-neutron quasiparticle random-phase approximation. The underlying mean field is described self-consistently from deformed Skyrme Hartree-Fock calculations with pairing correlations. Residual separable particle-hole and particle-particle forces are also included in the formalism. The structural evolution in these isotopic chains including both even and odd isotopes is analyzed in terms of the equilibrium deformed shapes. Gamow-Teller strength distributions, beta-decay half-lives, and beta-delayed neutron-emission probabilities are studied, stressing their relevance to describe the path of the nucleosynthesis rapid neutron capture process.
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