C. A. Ur

University of Bonn, Bonn, North Rhine-Westphalia, Germany

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Publications (520)

  • Article · Sep 2016 · Physica Scripta
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    [Show abstract] [Hide abstract] ABSTRACT: Shape parameters of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in ^{42}Ca 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∼40 mass region is discussed. Furthermore, the potential of Coulomb excitation as a tool to study superdeformation has been demonstrated for the first time.
    Full-text Article · Aug 2016 · Physical Review Letters
  • [Show abstract] [Hide abstract] ABSTRACT: The multipolarity of the main transition leading to the ground state in Bi210 was investigated using the angular correlations of γ rays. The analyzed γ-coincidence data were obtained from the Bi209(n,γ)Bi210 experiment performed at Institut Laue-Langevin Grenoble at the PF1B cold-neutron facility. The EXILL (EXOGAM at the ILL) multidetector array, consisting of 16 high-purity germanium detectors, was used to detect γ transitions. The mixing ratio of the 320-keV γ ray was defined by minimizing a multivariable χΣ2 function constructed from the coefficients of angular correlation functions for seven pairs of strong transitions in Bi210. As a result, the almost pure M1 multipolarity of the 320-keV γ ray was obtained, with an E2 admixture of less than 0.6% only (95% confidence limit). Based on this multipolarity the neutron-capture cross section leading to the ground state in Bi210, that decays in turn to radiotoxic Po210, was determined to be within the limits 21.3(9) and 21.5(9) mb. This result is important for nuclear reactor applications.
    Article · Jul 2016
  • H.R. Weller · C.A. Ur · C. Matei · [...] · Z. Yasin
    Article · Jun 2016 · Romanian Reports in Physics
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    [Show abstract] [Hide abstract] ABSTRACT: Excited states in 157Dy have been studied by γ-γ coincidence measurements via the reaction 124Sn(36S,3n) at a beam energy of 155MeV. Lifetimes of the relatively lower-spin states in 157Dy were measured by means of the Recoil Distance Dopplershift technique in the coincidence mode. The experiment was performed at the Laboratori Nazionali di Legnaro with the GASP array and the Cologne plunger device. With the same setup a Doppler- shift attenuation (DSA) lifetime measurement was performed for the higher spin states. The Differential decay-curve method was applied for the lifetime determination.
    Full-text Article · Jun 2016 · Journal of Physics Conference Series
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    B.M. Nyakó · J. Timár · M. Csatlós · [...] · C.A. Ur
    [Show abstract] [Hide abstract] ABSTRACT: Medium-spin excited states of the neutron-rich 87Br and 89Br nuclei were observed and studied for the first time. They were populated in fission of 235U induced by the cold-neutron beam of the PF1B facility of the Institut Laue-Langevin, Grenoble. The measurement of γ radiation following fission has been performed using the EXILL array of Ge detectors. The observed level schemes were compared with results of large valence space shell model calculations. Both medium-spin level schemes consist of band-like structures, which can be understood as bands built on the πf 5/2, πp 3/2 and πg 9/2 configurations. Both nuclei have 5/2− ground state spin-parity contrary to the odd-mass Br isotopes containing fewer neutrons, which have 3/2− ground state spin-parity. On the basis of the properties of the πg 9/2 decoupled bands the deformations of the 87Br and 89Br fit to the systematics of nuclei in the region. 87Br is close to the vibrational limit, while 89Br is more rotational.
    Full-text Article · Jun 2016 · Journal of Physics Conference Series
  • [Show abstract] [Hide abstract] ABSTRACT: We performed a γ -particle coincidence experiment for the 60Ni+116Sn system to investigate whether thepopulation of the two-neutron pickup channel leading to 62Ni 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 experimenthas been performed by employing the PRISMA magnetic spectrometer coupled to theAdvanced Gamma TrackingArray (AGATA) demonstrator. The strength distribution of excited states corresponding to the inelastic, one- andtwo-neutron transfer channels has been extracted.We found that in the two-neutron transfer channel the strengthto excited states corresponds to a fraction (less than 24%) of the total, consistent with the previously obtainedresults that the 2n channel is dominated by the ground-state to ground-state transition.
    Article · May 2016
  • [Show abstract] [Hide abstract] ABSTRACT: The Extreme Light Infrastructure - Nuclear Physics facility will deliver brilliant gamma beams with high spectral density and a high degree of polarization starting in 2018 in Bucharest-Magurele, Romania. Several monitoring instruments are proposed for measuring the spectral, temporal, and spatial characteristics of the gamma beam. The d(γ,n)p reaction has been investigated for its use in determining the gamma beam parameters in a series of measurements carried out at the High Intensity Gamma Source, Durham, U.S.A.. Measurements of the emitted neutrons have been performed using liquid scintillator and 6Li-glass neutron detectors at several incident gamma energies between 2.5 to 20 MeV . The experimental results presented in this paper have shown that an instrument based on the d(γ,n)p reaction can be used to monitor the intensity and polarization of the gamma beam to be produced at ELI-NP.
    Article · May 2016 · Journal of Instrumentation
  • [Show abstract] [Hide abstract] ABSTRACT: The low-spin structure of the 210Bi nucleus was investigated in the neutron capture experiment 209Bi(n,γ )210Biperformed at ILL Grenoble at the PF1B cold-neutron facility. By using the EXILL multidetector array, consistingof 46 high-purity germanium crystals, and γγ-coincidence technique, 64 primary γ rays were observed (40new) and a total number of 70 discrete states (33 new) were located below the neutron binding energy in 210Bi.The analysis of the angular correlations of γ rays provided information about transitions multipolarities, whichmade it possible to confirm most of the previously known spin-parity assignments and helped establish new ones.The obtained experimental results were compared to shell-model calculations involving one-valence-proton,one-valence-neutron excitations outside the 208Pb core. It has been found that while up to the energy of ∼2 MeVeach state observed in 210Bi has its calculated counterpart; at higher excitation energies some levels cannot bedescribed by the valence particle couplings. These states may arise from couplings of valence particles to the 3−octupole phonon of the doubly magic 208Pb core and may serve as a testing ground for models which describesingle particle-phonon excitations.
    Article · May 2016
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    A Vogt · B Birkenbach · P Reiter · [...] · C Y Wu
    [Show abstract] [Hide abstract] ABSTRACT: Detailed spectroscopic information on the N∼82 nuclei is necessary to benchmark shell-model calculations in the region. The nuclear structure above long-lived isomers in Xe134 is investigated after multinucleon transfer (MNT) and actinide fission. Xenon-134 was populated as (i) a transfer product in Xe136+U238 and Xe136+Pb208 MNT reactions and (ii) as a fission product in the Xe136+U238 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 Xe136+Pt198 MNT reaction was studied with the γ-ray spectrometer GAMMASPHERE in combination with the gas detector array Compact Heavy Ion Counter (CHICO). Several high-spin states in Xe134 on top of the two long-lived isomers are discovered based on γγ-coincidence relationships and information on the γ-ray angular distributions as well as excitation energies from the total kinetic energy loss and fission fragments. The revised level scheme of Xe134 is extended up to an excitation energy of 5.832 MeV with tentative spin-parity assignments up to 16+. Previous assignments of states above the 7- isomer are revised. Latest shell-model calculations employing two different effective interactions reproduce the experimental findings and support the new spin and parity assignments.
    Full-text Article · May 2016
  • [Show abstract] [Hide abstract] ABSTRACT: The γ decay from the high-lying states of Ce140 excited via inelastic scattering of O17 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 ΔE-E silicon detectors. Angular distributions of scattered ions and emitted γ 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 α 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.
    Article · Apr 2016
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    [Show abstract] [Hide abstract] ABSTRACT: The GERDA (GERmanium Detector Array) is an experiment for the search of neutrinoless double beta decay ( ) in 76Ge, located at Laboratori Nazionali del Gran Sasso of INFN (Italy). In the first phase of the experiment, a 90% confidence level (C.L.) sensitivity of on the decay half-life was achieved with a 21.6 kg⋅yr exposure and an unprecedented background index in the region of interest of 10−2 counts/(keV⋅kg⋅yr). No excess of signal events was found, and an experimental lower limit on the half-life of 2.1 ⋅ 1025 yr (90% C.L.) was established. Correspondingly, the limit on the effective Majorana neutrino mass is , depending on the considered nuclear matrix element. The previous claim for evidence of a decay signal is strongly disfavored, and the field of research is open again.
    Full-text Article · Apr 2016
  • [Show abstract] [Hide abstract] ABSTRACT: The PRISMA spectrometer’s response function was successfully applied to match three angular and magnetic settings over a wide angular range for measurements of quasi-elastic reactions in 40Ar + 208Pb. The absolute scale of cross sections has been obtained by using the Rutherford cross section at the forward angles and the information from the energy distributions measured with the spectrometer without and with coincidences with the CLARA γ-array. The semi-classical model GRAZING has been used to test the unfolding procedure and for comparison with the corrected cross sections.
    Article · Apr 2016 · European Physical Journal A
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    G. Bocchi · S. Leoni · B. Fornal · [...] · V. Vedia
    [Show abstract] [Hide abstract] ABSTRACT: The gamma-ray decay of excited states of the one-valence-proton nucleus 133Sb has been studied using cold-neutron induced fission of 235U and 241Pu targets, during the EXILL campaign at the ILL reactor in Grenoble. By using a highly efficient HPGe array, coincidences between gamma-rays prompt with the fission event and those delayed up to several tens of microseconds were investigated, allowing to observe, for the first time, high-spin excited states above the 16.6 micros isomer. Lifetimes analysis, performed by fast-timing techniques with LaBr3(Ce) scintillators, reveals a difference of almost two orders of magnitude in B(M1) strength for transitions between positive-parity medium-spin yrast states. The data are interpreted by a newly developed microscopic model which takes into account couplings between core excitations (both collective and non-collective) of the doubly magic nucleus 132Sn and the valence proton, using the Skyrme effective interaction in a consistent way. The results point to a fast change in the nature of particle-core excitations with increasing spin.
    Full-text Article · Mar 2016 · Physics Letters B
  • M. Czerwinski · T. Rzaca-Urban · W. Urban · [...] · C.A. Ur
    [Show abstract] [Hide abstract] ABSTRACT: Medium-spin excited levels in Rb90, populated in the fission of U235 induced by neutrons, have been observed for the first time. γ radiation from fission has been measured by using the EXILL array of Ge detectors at the cold-neutron-beam facility PF1B of the Institut Laue–Langevin, Grenoble. Low-energy levels are interpreted as members of the πp3/2−1ν(d5/2)3, πf5/2−1ν(d5/2)3, and πg9/2ν(d5/2)3 multiplets with the 0− ground state due to the seniority-3 coupling in the νd5/2 shell. Analogous anomalous coupling within the πg9/2ν(d5/2)3 configuration explains the 5+, 6+, and 7+ triplet of states, observed at medium spins, similar to the triplet seen in the N=53 isotone, Br88. Shell-model calculations reproduce well the proposed structures in Rb88,90 and support the seniority-3 coupling in N=53 isotones and its absence in N=51 isotones. The structure of the odd-odd Rb88 and Rb90 nuclei provides an argument in favor of the collectivity building up at the neutron number N=53.
    Article · Mar 2016
  • [Show abstract] [Hide abstract] ABSTRACT: Lifetimes of yrast and nonyrast states of Pd102 populated via the Zr92(C13, 3n) reaction are measured by means of the recoil distance Doppler-shift technique with a Cologne plunger coupled to a GASP spectrometer. The event-by-event data accumulated at 24 plunger distances in the range of 0.1 μm to 9 mm are analyzed using the differential decay curve method. The resulting B(E2) values of the γ transitions depopulating yrast-band members up to the Iπ=8+ state are found to deviate significantly from the corresponding predictions of the E(5) critical-point symmetry.
    Article · Jan 2016
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    P Bringel · H Hubel · H Amro · [...] · C Ur
    [Show abstract] [Hide abstract] ABSTRACT: Cited References Count:22|SPRINGER-VERLAG|175 FIFTH AVE, NEW YORK, NY 10010 USA|Bringel, P|Hubel, H|Amro, H|Axiotis, M|Bazzacco, D|Bhattacharya, S|Bhowmik, R|Domscheit, J|Hagemann, GB|Jensen, DR|Kroll, T|Lunardi, S|Napoli, DR|Neusser, A|Pancholi, SC|Petrache, CM|Schonwasser, G|Singh, AK|Ur, C|ISI Document Delivery No.:655XT
    Full-text Article · Jan 2016 · European Physical Journal A
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    Full-text Article · Jan 2016 · Acta Physica Polonica Series B
  • [Show abstract] [Hide abstract] ABSTRACT: Detailed spectroscopic information on the N∼82 nuclei is necessary to benchmark shell-model calculations in the region. The nuclear structure above long-lived isomers in Xe134 is investigated after multinucleon transfer (MNT) and actinide fission. Xenon-134 was populated as (i) a transfer product in Xe136+U238 and Xe136+Pb208 MNT reactions and (ii) as a fission product in the Xe136+U238 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 Xe136+Pt198 MNT reaction was studied with the γ-ray spectrometer GAMMASPHERE in combination with the gas detector array Compact Heavy Ion Counter (CHICO). Several high-spin states in Xe134 on top of the two long-lived isomers are discovered based on γγ-coincidence relationships and information on the γ-ray angular distributions as well as excitation energies from the total kinetic energy loss and fission fragments. The revised level scheme of Xe134 is extended up to an excitation energy of 5.832 MeV with tentative spin-parity assignments up to 16+. Previous assignments of states above the 7− isomer are revised. Latest shell-model calculations employing two different effective interactions reproduce the experimental findings and support the new spin and parity assignments.
    Article · Jan 2016
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    [Show abstract] [Hide abstract] ABSTRACT: The experimental setup GAMIPE used for gyro magnetic factor measurements at Laboratori Nazionali di Legnaro and a recent experimental work regarding K-isomers in 174W are described. Aim of the experiment is to study the detailed structure of the isomeric states wave functions, by the measurement of the magnetic dipole moments. This piece of information can provide interesting hints for theoretical models. Preliminary results concerning the population of the isomers of interest and half-lives are presented.
    Full-text Article · Jan 2016 · The European Physical Journal Conferences

Publication Stats

4k Citations

Institutions

  • 2016
    • University of Bonn
      • Helmholtz-Institut für Strahlen- und Kernphysik
      Bonn, North Rhine-Westphalia, Germany
  • 1999-2015
    • University of Padova
      • Department of Information Engineering
      Padua, Veneto, Italy
    • KTH Royal Institute of Technology
      Tukholma, Stockholm, Sweden
    • University of Texas at Dallas
      Richardson, Texas, United States
  • 1999-2014
    • INFN - Istituto Nazionale di Fisica Nucleare
      • Laboratori Nazionali di Legnaro LNL
      Frascati, Latium, Italy
    • Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering
      • Department of Nuclear Physics (DFN-TANDEM)
      București, Bucureşti, Romania
  • 2013
    • Max Planck Institute of Physics
      München, Bavaria, Germany
    • Technische Universität München
      München, Bavaria, Germany
  • 2009
    • University of the West of Scotland
      • School of Engineering
      Paisley, SCT, United Kingdom
  • 1996-2009
    • Horia Hulubei National Institute of Physics and Nuclear Engineering
      Bucureşti, Bucureşti, Romania
    • University Joseph Fourier - Grenoble 1
      • Laboratoire de Physique Subatomique et Cosmologie
      Grenoble, Rhône-Alpes, France
  • 2003
    • Institute for Nuclear Research, Romania
      Piteshti, Argeş, Romania
  • 2001-2002
    • University of Cologne
      • Institute for Nuclear Physics
      Köln, North Rhine-Westphalia, Germany
    • Universidad de Salamanca
      Helmantica, Castille and León, Spain