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AGATA Collaboration(Hadynska-Klek, K. et al), & Gadea, A. (2016). Superdeformed and Triaxial States in Ca-42. Phys. Rev. Lett., 117(6), 062501–7pp.
Abstract: Shape parameters of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in Ca-42 were determined from E2 matrix elements measured in the first low-energy Coulomb excitation experiment performed with AGATA. The picture of two coexisting structures is well reproduced by new state-of-the-art large-scale shell model and beyond-mean-field calculations. Experimental evidence for superdeformation of the band built on 0(2)(+) has been obtained and the role of triaxiality in the A similar to 40 mass region is discussed. Furthermore, the potential of Coulomb excitation as a tool to study superdeformation has been demonstrated for the first time.
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AGATA Collaboration(Krzysiek, M. et al), & Gadea, A. (2016). Gamma decay of the possible 1(-) two-phonon state in Ce-140 excited via inelastic scattering of O-17. Acta Phys. Pol. B, 47(3), 859–866.
Abstract: The gamma decay from the low-lying dipole states of Ce-140 excited via inelastic scattering of O-17 at 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 of the TRACE array. Particular attention is here given to the decay of the first 1(-) state at 3643 keV which is considered to be of two-phonon character. The gamma-gamma coincidence method was applied to select desired decay branch. No direct decay from this state was observed to 2(+) and 3(-) phonon states which would be the proof of the pure harmonic coupling. The comparison between experimentally obtained differential cross sections and analysis with distorted wave Born approximation (DWBA) allowed to conclude that the first 1(-) state has a different nature than higher-lying pygmy dipole states. This was possible using the form factor obtained by folding a microscopically calculated transition density.
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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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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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Agramunt, J. et al, Tain, J. L., Albiol, F., Algora, A., Domingo-Pardo, C., Jordan, M. D., et al. (2016). Characterization of a neutron-beta counting system with beta-delayed neutron emitters. Nucl. Instrum. Methods Phys. Res. A, 807, 69–78.
Abstract: A new detection system for the measurement of beta-delayed neutron emission probabilities has been characterized using fission products with well known beta-delayed neutron emission properties. The setup consists of BELEN-20, a 4 pi-neutron counter with twenty He-3 proportional tubes arranged inside a large polyethylene neutron moderator, a thin Si detector for beta counting and a self-triggering digital data acquisition system. The use of delayed-neutron precursors with different neutron emission windows allowed the study of the effect of energy dependency on neutron, beta and beta-neutron rates. The observed effect is well reproduced by Monte Carlo simulations. The impact of this dependency on the accuracy of neutron emission probabilities is discussed. A new accurate value of the neutron emission probability for the important delayed-neutron precursor I-137 was obtained, P-n = 7.76(14)%.
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