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Ertoprak, A. et al, Algora, A., Gadea, A., & Huyuk, T. (2018). M1 and E2 transition rates from core-excited states in semi-magic Ru-94. Eur. Phys. J. A, 54(9), 145–9pp.
Abstract: Lifetimes of high-spin states have been measured in the semi-magic (N = 50) nucleus Ru-94. Excited states in Ru-94 were populated in the Ni-58(Ca-40, 4p)Ru-94* fusion-evaporation reaction at the Grand Accelerateur National d'Ions Lourds (GANIL) accelerator complex. DSAM lifetime analysis was performed on the Doppler broadened line shapes in energy spectra obtained from gamma-rays emitted while the residual nuclei were slowing down in a thick 6 mg/cm(2) metallic Ni-58 target. In total eight excited-state lifetimes in the angular momentum range I = (13-20)h have been measured, five of which were determined for the first time. The corresponding B(M1) and B(E2) reduced transition strengths are discussed within the framework of large-scale shell model calculations to study the contribution of different particle-hole configurations, in particular for analyzing contributions from core-excited configurations.
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AGATA Collaboration(Cederwall, B. et al), Gadea, A., Jurado, M., Domingo-Pardo, C., Huyuk, T., & Perez-Vidal, R. M. (2020). Isospin Properties of Nuclear Pair Correlations from the Level Structure of the Self-Conjugate Nucleus Ru-88. Phys. Rev. Lett., 124(6), 062501–6pp.
Abstract: The low-lying energy spectrum of the extremely neutron-deficient self-conjugate (N = Z) nuclide Ru-88(44)44 has been measured using the combination of the Advanced Gamma Tracking Array (AGATA) spectrometer, the NEDA and Neutron Wall neutron detector arrays, and the DIAMANT charged particle detector array. Excited states in Ru-88 were populated via the Fe-54(Ar-36, 2n gamma)Ru-88* fusion-evaporation reaction at the Grand Accelerateur National d'Ions Lourds (GANIL) accelerator complex. The observed gamma-ray cascade is assigned to Ru-88 using clean prompt gamma-gamma-2-neutron coincidences in anticoincidence with the detection of charged particles, confirming and extending the previously assigned sequence of low-lying excited states. It is consistent with a moderately deformed rotating system exhibiting a band crossing at a rotational frequency that is significantly higher than standard theoretical predictions with isovector pairing, as well as observations in neighboring N > Z nuclides. The direct observation of such a “delayed” rotational alignment in a deformed N = Z nucleus is in agreement with theoretical predictions related to the presence of strong isoscalar neutron-proton pair correlations.
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Egea, F. J. et al, Gadea, A., Barrientos, D., & Huyuk, T. (2013). Design and Test of a High-Speed Flash ADC Mezzanine Card for High-Resolution and Timing Performance in Nuclear Structure Experiments. IEEE Trans. Nucl. Sci., 60(5), 3526–3531.
Abstract: This work describes new electronics for the EX-OGAM2 (HP-Ge detector array) and NEDA (BC501A-based neutron detector array). A new digitizing card with high resolution has been designed for gamma-ray and neutron spectroscopy experiments. The higher bandwidth requirement of the NEDA signals, together with the necessity for accuracy, require a high sampling rate in order to preserve the shape for real-time Pulse Shape Analysis (PSA). The PSA is of paramount importance for the NEDA to discriminate between neutrons and gamma-ray signals. Both high resolution and high speed parameters are often difficult to achieve in a single electronic unit. These constraints, together with the need to build new digitizing electronics to improve performance and flexibility of signal analysis in nuclear physics experiments, led to the development a new FADC mezzanine card. In this work, the design and development are described, including the characterization procedure and the preliminary measurement results.
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AGATA Collaboration(Louchart, C. et al), Gadea, A., & Huyuk, T. (2013). Collective nature of low-lying excitations in 70,72,74Zn from lifetime measurements using the AGATA spectrometer demonstrator. Phys. Rev. C, 87(5), 054302–10pp.
Abstract: Background: Neutron-rich nuclei with protons in the fp shell show an onset of collectivity around N=40. Spectroscopic information is required to understand the underlying mechanism and to determine the relevant terms of the nucleon-nucleon interaction that are responsible for the evolution of the shell structure in this mass region. Methods: We report on the lifetime measurement of the first 2+ and 4+ states in 70,72,74Zn and the first 6+ state in 72Zn using the recoil distance Doppler shift method. The experiment was carried out at the INFN Laboratory of Legnaro with the AGATA demonstrator, first phase of the Advanced Gamma Tracking Array of highly segmented, high-purity germanium detectors coupled to the PRISMA magnetic spectrometer. The excited states of the nuclei of interest were populated in the deep inelastic scattering of a 76Ge beam impinging on a 238U target. Results: The maximum of collectivity along the chain of Zn isotopes is observed for 72Zn at N=42. An unexpectedly long lifetime of 20−5.2+1.8 ps was measured for the 4+ state in 74Zn. Conclusions: Our results lead to small values of the B(E2;41+→21+)/B(E2;21+→01+) ratio for 72,74Zn, suggesting a significant noncollective contribution to these excitations. These experimental results are not reproduced by state-of-the-art microscopic models and call for lifetime measurements beyond the first 2+ state in heavy zinc and nickel isotopes.
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Krzysiek, M. et al, Gadea, A., Huyuk, T., & Barrientos, D. (2014). Study of the soft dipole modes in Ce-140 via inelastic scattering of O-17. Phys. Scr., 89(5), 054016–6pp.
Abstract: The main aim of this study was a deeper understanding of the nuclear structure properties of the soft dipole modes in Ce-140, excited via inelastic scattering of weakly bound O-17 projectiles. An important aim was to investigate the 'splitting' of the PDR into two parts: a low-energy isoscalar component dominated by neutron-skin oscillations and a higher-energy component lying on the tail of the giant dipole resonance of a rather isovector character. This was already observed for this nucleus, investigated in (alpha, alpha') and (gamma,gamma') experiments. The experiment was performed at Laboratori Nazionali di Legnaro, Italy. Inelastic scattering of O-17 ion beam at 20 MeV A(-1) was used to excite the resonance modes in the Ce-140 target. Gamma-rays were registered by five triple clusters of AGATA-Demonstrator and nine large volume scintillators (LaBr3). The scattered O-17 ions were identified by two Delta E – E Si telescopes of the TRACE array mounted inside the scattering chamber. The telescopes consisted of two segmented Si-pad detectors, each of 60 pixels. Very preliminary data have shown a strong domination of the E1 transitions in the 'pygmy' region with a character more similar to the one obtained in alpha scattering experiment.
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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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Moradi, F. G. et al, & Huyuk, T. (2014). Spectroscopy of the neutron-deficient N=50 nucleus Rh-95. Phys. Rev. C, 89(4), 044310–8pp.
Abstract: The neutron-deficient semimagic (neutron number N = 50) Rh-95 nucleus has been produced at high spins using the projectile-target system Ca-40 + Ni-58 at 125 MeV beam energy. The gamma-decays of levels populated by the 3p fusion evaporation reaction channel were studied using gamma-gamma coincidences, and 20 new gamma-ray transitions involving 15 new positive-and negative-parity states were observed. Spin and parity for many of the excited states were firmly deduced for the first time using the combined directional angular correlation and direction-polarization techniques. The observed structures are discussed within the framework of large-scale shell model calculations. E1 transition strengths were deduced and used together with the results of the shell model calculations to study the contribution of different particle-hole configurations, in particular for analyzing contributions from core-excited configurations.
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Dijon, A. et al, Gadea, A., & Huyuk, T. (2012). Discovery of a new isomeric state in Ni-68: Evidence for a highly deformed proton intruder state. Phys. Rev. C, 85(3), 031301–5pp.
Abstract: We report on the observation of a new isomeric state in Ni-68. We suggest that the newly observed state at 168(1) keV above the first 2(+) state is a pi(2p-2h) 0(+) state across the major Z = 28 shell gap. Comparison with theoretical calculations indicates a pure proton intruder configuration and the deduced low-lying structure of this key nucleus suggests a possible shape coexistence scenario involving a highly deformed state.
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Doncel, M. et al, Gadea, A., & Huyuk, T. (2013). Lifetime measurements in neutron-rich Cu isotopes. Acta Phys. Pol. B, 44(3), 505–510.
Abstract: The nuclear structure of neutron-rich nuclei close to the double-magic nucleus Ni-78 has been investigated by measuring the lifetime of excited states. In this contribution, it will be presented the lifetime of the J(pi) = 7/2(-) excited state at 981 keV of the Cu-71 isotope, measured using the AGATA Demonstrator coupled to the PRISMA spectrometer and the Koln plunger setup. This is the first time this combined setup has been used for a lifetime measurement.
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Vandone, V. et al, Gadea, A., & Huyuk, T. (2013). Global properties of K hindrance probed by the gamma decay of the warm rotating W-174 nucleus. Phys. Rev. C, 88(3), 034312–9pp.
Abstract: The K hindrance to the gamma decay is studied in the warm rotating W-174 nucleus, focusing on the weakening of the selection rules of the K quantum number with increasing excitation energy. W-174 was populated by the fusion reaction of Ti-50 (at 217 MeV) on a Te-128 target, and its gamma decay was detected by the AGATA Demonstrator array coupled to a BaF2 multiplicity filter at Laboratori Nazionali di Legnaro of INFN. A fluctuation analysis of gamma coincidence matrices gives a similar number of low-K and high-K discrete excited bands. The results are compared to simulations of the gamma-decay flow based on a microscopic cranked shell model at finite temperature in which the K mixing is governed by the interplay of Coriolis force with the residual interaction. Agreement between simulations and experiment is obtained only by hindering the E1 decay between low-K and high-K bands by an amount compatible with that determined by spectroscopic studies of K isomers in the same mass region, with a similar trend with excitation energy. The work indicates that K mixing due to temperature effects may play a leading role for the entire body of discrete excited bands, which probes the onset region of K weakening.
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