C. A. Ur

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

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Publications (530)

  • Source
    [Show abstract] [Hide abstract] ABSTRACT: The ROmanian array for SPectroscopy in HEavy ion REactions (ROSPHERE) has been designed as a multi-detector setup dedicated to γ-ray spectroscopy studies at the Bucharest 9 MV Tandem accelerator. Consisting of up to 25 detectors (either Compton suppressed HPGe detectors or fast LaBr3(Ce) scintillator detectors) together with a state of the art plunger device, ROSPHERE is a powerful tool for lifetime measurements using the Recoil Distance Doppler Shift (RDDS) and the in-beam Fast Electronic Scintillation Timing (FEST) methods. The array's geometry, detectors, electronics and data acquisition system are described. Selected results from the first experimental campaigns are also presented.
    Full-text available · Article · Nov 2016 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
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    [Show abstract] [Hide abstract] ABSTRACT: The development of high power lasers and the combination of such novel devices with accelerator technology has enlarged the science reach of many research fields, in particular particle and nuclear physics, astrophysics as well as societal applications in material science, nuclear energy and applications for medicine. The European Strategic Forum for Research Infrastructures has selected a proposal based on these new premises called the Extreme Light Infrastructure (ELI). The ELI will be built as a network of three complementary pillars at the frontier of laser technologies. The ELI-NP pillar (NP for nuclear physics) is under construction near Bucharest (Romania) and will develop a scientific program using two 10 PW lasers and a Compton back-scattering high-brilliance and intense low-energy gamma beam, a combination of laser and accelerator technology at the frontier of knowledge. This unique combination of beams that are unique worldwide allows us to develop an experimental program in nuclear physics at the frontiers of present-day knowledge as well as society driven applications. In the present paper, the technical description of the facility as well as the new perspectives in nuclear structure, nuclear reactions and nuclear astrophysics will be presented.
    Full-text available · Article · Sep 2016 · Physica Scripta
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    S. Ilieva · Th. Kröll · J.-M. Régis · [...] · N. Warr
    [Show abstract] [Hide abstract] ABSTRACT: Background: Lifetimes of nuclear excited states in fission fragments have been studied in the past following isotope separation, thus giving access mainly to the fragments’ daughters and only to long-lived isomeric states in the primary fragments. For the first time now, short-lived excited states in the primary fragments, produced in neutron-induced prompt fission of 235 U and 241Pu, were studied within the EXILL&FATIMA campaign at the intense neutron-beam facility of the Institute Laue-Langevin in Grenoble. Purpose: We aim to investigate the quadrupole collective properties of neutron-rich even-even 138,140,142 Xe isotopes lying between the double shell closure N = 82 and Z = 50 and a deformed region with octupole collectivity. Method: The γ rays emitted from the excited fragments were detected with a mixed array consisting of 8 HPGe EXOGAM Clover detectors (EXILL) and 16 LaBr3 (Ce) fast scintillators (FATIMA). The detector system has the unique ability to select the interesting fragment making use of the high resolution of the HPGe detectors and determine subnanosecond lifetimes using the fast scintillators. For the analysis the generalized centroid difference method was used. Results: We show that quadrupole collectivity increases smoothly with increasing neutron number above the closed N = 82 neutron shell. Our measurements are complemented by state-of-the-art theory calculations based on shell-model descriptions. Conclusions: The observed smooth increase in quadrupole collectivity is similar to the evolution seen in the measured masses of the xenon isotopic chain and is well reproduced by theory. This behavior is in contrast to higher Z even-even nuclei where abrupt change in deformation occurs around N = 90.
    Full-text available · Article · Sep 2016 · Physical Review C
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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 available · 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
    [Show abstract] [Hide abstract] ABSTRACT: The high brilliance Gamma Beam System at ELI-NP is based on the Inverse Compton Scattering of laser light on relativistic electron bunches provided by a warm radio-frequency linear accelerator. The system will deliver quasi-monochromatic gamma-ray beams (bandwidth 0.5%) with a high spectral density (10,000 photons/s/eV) and high degree of linear polarization (99%). The system will be delivered by the EuroGammaS Association, a European consortium of academic and research institutions and commercial companies with well-established expertise in the field. Optimization and monitoring of the Gamma Beam System requires the proper means for accurately measuring the spatial, spectral and temporal characteristics of the gamma-ray beams. The system will be delivered by the EuroGammaS Association with a set of devices for the optimization of the gamma-ray beam characteristics to be used during the initial phase of setting up the system. The present TDR is dealing with additional equipment and techniques, complementary to the ones provided by EuroGammaS, required to deliver the gamma-ray beams to the experimental setups and to monitor the characteristics of the beams during the performance of the experiments. Consequently, there are two main categories of equipment to be considered: a) equipment for the delivery of the gamma-ray beam to users including beam pipes, vacuum systems, collimators, alignment platforms, shielding, and beam dumps; b) diagnostics and monitor devices to be used during the operation of the gamma beam system. An extensive description of the equipment and devices needed for beam delivery, diagnostics and monitoring is given in Section 2 of this document. The development, construction and installation of the delivery, diagnostic and monitoring equipment is strongly related to the phases of installation of the Gamma Beam System and the corresponding properties of the gamma-ray beam at each phase. The development and building of the devices is scheduled according to these phases. The development of beam diagnostics and monitor devices is done within an international collaboration and it will take advantage of the know-how elaborated at other gamma-ray beam facilities presently in operation such as BITS at TUNL/Duke University.
    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 available · 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 available · 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 available · 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 available · 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 available · 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 available · Article · Jan 2016 · European Physical Journal A
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    Călin A. Ur · Dan Filipescu · Ioana Gheorghe · [...] · Ovidiu Teşileanu
    [Show abstract] [Hide abstract] ABSTRACT: The Extreme Light Infrastructure - Nuclear Physics facility is dedicated to nuclear physics studies with the use of extreme electromagnetic radiation. One of the main research system to be installed and operated in the facility is an outstanding high brilliance gamma beam system. The Gamma Beam System of ELI–NP will produce intense, quasi–monochromatic gamma beams via inverse Compton scattering of short laser pulses on relativistic electron beam pulses. The gamma beams available at ELI–NP will allow for the performance of photo-nuclear reactions aiming to reveal the intimate structure of the atomic nucleus. Nuclear Resonance Fluorescence, photo-fission, photo-disintegration reactions above the particle threshold will be used to study the dipole response of nuclei, the structure of the Pygmy resonances, nuclear processes relevant for astrophysics, production and study of exotic neutron–rich nuclei.
    Full-text available · Article · Jan 2016 · The European Physical Journal Conferences

Publication Stats

5k Citations


  • 2016
    • University of Bonn
      • Helmholtz-Institut für Strahlen- und Kernphysik
      Bonn, North Rhine-Westphalia, Germany
    • GSI Helmholtzzentrum für Schwerionenforschung
      Darmstadt, Hesse, 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