AGATA Collaboration(Vogt, A. et al), & Gadea, A. (2017). Isomers and high-spin structures in the N=81 isotones Xe-135 and Ba-137. Phys. Rev. C, 95(2), 024316–17pp.
Abstract: The high-spin structures and isomers of the N = 81 isotones Xe-135 and Ba-137 are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in Xe-136+ U-238 and (ii) Xe-136+ Pb-208 MNT reactions employing the high-resolution Advanced Gamma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (iii) in the Xe-136+ Pt-198 MNT reaction employing the gamma-ray array GAMMASPHERE in combination with the gas-detector array CHICO, and (iv) via a B-11+ Te-130 fusion-evaporation reaction with the HORUS gamma-ray array at the University of Cologne. The high-spin level schemes of Xe-135 and Ba-137 are considerably extended to higher energies. The 2058-keV (19/2(-)) state in Xe-135 is identified as an isomer, closing a gap in the systematics along the N = 81 isotones. Its half-life is measured to be 9.0(9) ns, corresponding to a reduced transition probability of B(E2,19/2(-) -> 15/2(-)) = 0.52(6) W.u. The experimentally deduced reduced transition probabilities of the isomeric states are compared to shell-model predictions. Latest shell-model calculations reproduce the experimental findings generally well and provide guidance to the interpretation of the new levels.
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AGATA Collaboration(Klintefjord, M. et al), Gadea, A., & Perez-Vidal, R. M. (2017). Measurement of lifetimes in Fe-62,Fe-64, Co-61,Co-63, and Mn-59. Phys. Rev. C, 95(2), 024312–11pp.
Abstract: Lifetimes of the 4(1)(+) states in Fe-62,Fe-64 and the 11/2(1)(-) states in Co-61,Co-63 and Mn-59 were measured at the Grand Accelerateur National d'Ions Lourds (GANIL) facility by using the Advanced Gamma Tracking Array (AGATA) and the large-acceptance variable mode spectrometer (VAMOS++). The states were populated through multinucleon transfer reactions with a U-238 beam impinging on a Ni-64 target, and lifetimes in the picosecond range were measured by using the recoil distance Doppler shift method. The data show an increase of collectivity in the iron isotopes approaching N = 40. The reduction of the subshell gap between the nu 2p(1/2) and nu 1g(9/2) orbitals leads to an increased population of the quasi-SU(3) pair (nu 1g(9/2), nu 2d(5/2)), which causes an increase in quadrupole collectivity. This is not observed for the cobalt isotopes withN < 40 for which the neutron subshell gap is larger due to the repulsive monopole component of the tensor nucleon-nucleon interaction. The extracted experimental B(E2) values are compared with large-scale shell-model calculations and with beyond-mean-field calculations with the Gogny D1S interaction. A good agreement between calculations and experimental values is found, and the results demonstrate in particular the spectroscopic quality of the Lenzi, Nowacki, Poves, and Sieja (LNPS) shell-model interaction.
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Mijatovic, T., Szilner, S., Corradi, L., Montanari, D., Pollarolo, G., Fioretto, E., et al. (2016). Multinucleon transfer reactions in the Ar-40+Pb-208 system. Phys. Rev. C, 94(6), 064616–7pp.
Abstract: We measured multinucleon transfer reactions in the Ar-40 + Pb-208 system at an energy close to the Coulomb barrier, by employing the PRISMA magnetic spectrometer. We extracted differential and total cross sections of the different transfer channels, with a careful investigation of the total kinetic energy loss distributions. Comparisons between different systems having the same Pb-208 target and with projectiles going from neutron-poor to neutron-rich nuclei, i.e., Ca-40, Ni-58, and Ar-40, as well as between the data and GRAZING calculations have been carried out. The neutron-rich (stable) Ar-40 beam allowed us to get access to the channels involving proton pickup, whose behavior in connection with the production of neutron-rich heavy partner has been outlined.
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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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Montanari, D. et al, & Gadea, A. (2016). Pair neutron transfer in Ni-60+Sn-116 probed via gamma-particle coincidences. Phys. Rev. C, 93(5), 054623–6pp.
Abstract: We performed a gamma-particle coincidence experiment for the Ni-60 + Sn-116 system to investigate whether the population of the two-neutron pickup channel leading to Ni-62 is mainly concentrated in the ground-state transition, as has been found in a previous work [D. Montanari et al., Phys. Rev. Lett. 113, 052501 (2014)]. The experiment has been performed by employing the PRISMA magnetic spectrometer coupled to the Advanced Gamma Tracking Array (AGATA) demonstrator. The strength distribution of excited states corresponding to the inelastic, one-and two-neutron transfer channels has been extracted. We found that in the two-neutron transfer channel the strength to excited states corresponds to a fraction (less than 24%) of the total, consistent with the previously obtained results that the 2n channel is dominated by the ground-state to ground-state transition.
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AGATA Collaboration(Vogt, A. et al), & Gadea, A. (2016). High-spin structure of Xe-134. Phys. Rev. C, 93(5), 054325–12pp.
Abstract: Detailed spectroscopic information on the N similar to 82 nuclei is necessary to benchmark shell-model calculations in the region. The nuclear structure above long-lived isomers in Xe-134 is investigated after multinucleon transfer (MNT) and actinide fission. Xenon-134 was populated as (i) a transfer product in Xe-136 + U-238 and Xe-136 + Pb-208 MNT reactions and (ii) as a fission product in the Xe-136 + U-238 reaction employing the high-resolution Advanced Gamma Tracking Array (AGATA). Trajectory reconstruction has been applied for the complete identification of beamlike transfer products with the magnetic spectrometer PRISMA. The Xe-136 + Pt-198 MNT reaction was studied with the gamma-ray spectrometer GAMMASPHERE in combination with the gas detector array Compact Heavy Ion Counter (CHICO). Several high-spin states in Xe-134 on top of the two long-lived isomers are discovered based on gamma gamma-coincidence relationships and information on the gamma-ray angular distributions as well as excitation energies from the total kinetic energy loss and fission fragments. The revised level scheme of Xe-134 is extended up to an
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AGATA Collaboration(Krzysiek, M. et al), & Gadea, A. (2016). Pygmy dipole resonance in Ce-140 via inelastic scattering of O-17. Phys. Rev. C, 93(4), 044330–8pp.
Abstract: The gamma decay from the high-lying states of Ce-140 excited via inelastic scattering of O-17 at a bombarding energy of 340 MeV was measured using the high-resolution AGATA-demonstrator array in coincidence with scattered ions detected in two segmented Delta E-E silicon detectors. Angular distributions of scattered ions and emitted gamma rays were measured, as well as their differential cross sections. The excitation of 1(-) states below the neutron separation energy is similar to the one obtained in reactions with the alpha isoscalar probe. The comparison between the experimental differential cross sections and the corresponding predictions using the distorted-wave Born approximation allowed us to extract the isoscalar component of identified 1(-) pygmy states. For this analysis the form factor obtained by folding microscopically calculated transition densities and optical potentials was used.
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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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Nacher, E., Rubio, B., Algora, A., Cano-Ott, D., Tain, J. L., Gadea, A., et al. (2016). Observations of the Gamow-Teller resonance in the rare-earth nuclei above Gd-146 populated in beta decay. Phys. Rev. C, 93(1), 014308–13pp.
Abstract: The rare-earth region of the nuclear table around the quasi-doubly magic nucleus Gd-146 is one of the very few places in which the Gamow-Teller (GT) resonance can be populated in beta decay. The appropriate technique to study such a phenomenon is total absorption spectroscopy, thanks to which one can measure the B(GT) distribution in beta-decay experiments even when it is very fragmented and lies at high excitation energy in the daughter nucleus. Results on the GT resonance measured in the beta decay of the odd-Z, N = 83 nuclei Tb-148, Ho-150, and Tm-152 are presented in this work and compared with shell-model calculations. The tail of the resonance is clearly observed up to the limit imposed by the Q value. This observation is important in the context of the understanding of the “quenching” of the GT strength.
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Stahl, C. et al., & Gadea, A. (2015). Population of the 2(ms)(+) mixed-symmetry state of Ba-140 with the alpha-transfer reaction. Phys. Rev. C, 92(4), 044324–7pp.
Abstract: Background: Identification of proton-neutron mixed-symmetric one-quadrupole phonon excitations (the 2(ms)(+) states) of atomic nuclei provides information on the isovector part of the residual nucleon-nucleon interaction. It was predicted that the 2(ms)(+) state of particular nuclei close to the U(5) limit of the interacting boson model, in particular Ba-140, should be considerably populated by alpha-transfer reactions [C. E. Alonso et al., Phys. Rev. C 78, 017301 (2008)]. Purpose: We aim at the identification of the 2(ms)(+) mixed-symmetry state (MSS) of radioactive Ba-140 and investigate its population by the alpha-transfer reaction as a suitable tool to selectively populate MSSs and as a potential new signature for its mixed-symmetric character. Method: A gamma-ray spectroscopy experiment was performed in inverse kinematics in order to populate the 2(ms)(+) state of Ba-140 by alpha-transfer from a C-nat target on Xe-136 beam ions. The population of the candidate for the 2(ms)(+) state of Ba-140 was measured relative to the population of the 2(1)(+) state. Results: The candidate for the 2(ms)(+) state of Ba-140 was populated by a transfer three times weaker than predicted. Another 2(+) state that can be ruled out as the MSS was in turn as strongly populated by the a transfer as predicted for the MSS. Conclusions: The relative population of 2(+) states by alpha-transfer cannot serve as a new signature for MSSs, since other 2(+) states are also strongly populated. Nevertheless, the substantial population of the MSS candidate of Ba-140 by alpha transfer qualifies this type of reaction as suitable tool to excite MSSs and study their electromagnetic decay properties.
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