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Publications (36)31.3 Total impact

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    ABSTRACT: Measurements of elastic and inelastic scattering cross sections have been performed for 2.5 and 4.1 MeV neutrons incident on 155,156,157,158,160Gd. Angular distributions have been measured at both energies for the 0+, 2+, and 4+ members of the ground-state (gs) band of the even-even isotopes and for the 3/2-, 5/2-, and 7/2- levels of the gs band of the even-odd isotopes. Angular distributions for inelastic scattering from the 9/2- level of the gs band of 155Gd and 157Gd have also been measured at 4.1 MeV. These results together with previously measured s- and p-wave strength functions, potential scattering radii, and elemental total cross sections have been combined in an analysis based on coupled-channel semimicroscopic optical model potential (OMP) and statistical model calculations. The deformed OMP, an extension of our earlier work [E. Bauge, J.P. Delaroche, and M. Girod, Phys. Rev. C 48, 1118 (1998)], is built using a complex density-dependent effective interaction and deformed matter densities deduced from unconstrained, axially symmetric Hartree-Fock-Bogoliubov (HFB) calculations based on the Gogny force. The HFB calculations which describe quite nicely a wealth of results from electron scattering and Coulomb excitations measurements, lead to semimicroscopic OMP predictions in good agreement with the neutron scattering and reaction measurements. A phenomenological OMP analysis is also performed to compare the global properties of both potentials.
    Phys. Rev. C. 02/2000; 61(3).
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    ABSTRACT: Measurements of elastic and inelastic scattering cross sections have been performed for 2.5 and 4.1 MeV neutrons incident on 155,156,157,158,160Gd. Angular distributions have been measured at both energies for the 0+, 2+, and 4+ members of the ground-state (gs) band of the even-even isotopes and for the 3/2-, 5/2-, and 7/2- levels of the gs band of the even-odd isotopes. Angular distributions for inelastic scattering from the 9/2- level of the gs band of 155Gd and 157Gd have also been measured at 4.1 MeV. These results together with previously measured s- and p-wave strength functions, potential scattering radii, and elemental total cross sections have been combined in an analysis based on coupled-channel semimicroscopic optical model potential (OMP) and statistical model calculations. The deformed OMP, an extension of our earlier work [E. Bauge, J.P. Delaroche, and M. Girod, Phys. Rev. C 48, 1118 (1998)], is built using a complex density-dependent effective interaction and deformed matter densities deduced from unconstrained, axially symmetric Hartree-Fock-Bogoliubov (HFB) calculations based on the Gogny force. The HFB calculations which describe quite nicely a wealth of results from electron scattering and Coulomb excitations measurements, lead to semimicroscopic OMP predictions in good agreement with the neutron scattering and reaction measurements. A phenomenological OMP analysis is also performed to compare the global properties of both potentials.
    Physical Review C 01/2000; 61(5). · 3.72 Impact Factor
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    ABSTRACT: Angular distributions for elastic and inelastic neutron scattering on 208Pb have been measured for the ground state and for excited states at 2.164 MeV (3-), 3.198 MeV (5-), 4.076 MeV (2+) and 4.323 MeV (4+) +4.425 MeV (6+), at incident energies between 7.5 and 15.5 MeV. Semi-microscopic folding-model calculations of the cross sections have been performed with the microscopic optical model of Jeukenne, Lejeune and Mahaux together with a Hartree-Fock-Bogoluybov ground state nucleon density and RPA transition densities. The nucleon excitation strenghts deduced in this study will be compared to values obtained at higher energies and with other projectiles.
    01/1985;
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    ABSTRACT: Nuclear deformation of the s-d shell nuclei /sup 24/Mg, /sup 28/Si, and /sup 32/S has been investigated by means of fast neutron scattering. Differential cross sections have been measured at the incident neutron energies of 9.76 and 14.83 MeV, over the angular range from 15/sup 0/ to 160/sup 0/. Angular distributions have been obtained for the elastic scattering and the inelastic scattering to low lying collective states. The measurements have been compared to the predictions of collective models, and nuclear deformations have been determined for these nuclei. The coupled-channel and compound-nucleus formalisms were used in the calculations. The analysis shows that these nuclei exhibit quite different shapes, and confirms the oblate deformation of /sup 28/Si established in recent works. A detailed comparison of the deformations obtained in this study with those deduced from (p,p'), (d,d'), (..cap alpha..,..cap alpha..'), (/sup 16/O, /sup 16/O'), other (n,n'), and charge distribution measurements is presented and discussed. It is emphasized that for these N = Z nuclei the quadrupole deformations and deformation lengths are in very good agreement when measured through neutron and proton scattering as well as electromagnetic excitations.
    Phys. Rev. C. 12/1984;
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    ABSTRACT: Nuclear deformation of the s-d shell nuclei 24Mg, 28Si, and 32S has been investigated by means of fast neutron scattering. Differential cross sections have been measured at the incident neutron energies of 9.76 and 14.83 MeV, over the angular range from 15° to 160°. Angular distributions have been obtained for the elastic scattering and the inelastic scattering to low lying collective states. The measurements have been compared to the predictions of collective models, and nuclear deformations have been determined for these nuclei. The coupled-channel and compound-nucleus formalisms were used in the calculations. The analysis shows that these nuclei exhibit quite different shapes, and confirms the oblate deformation of 28Si established in recent works. A detailed comparison of the deformations obtained in this study with those deduced from (p,p'), (d,d'), (α,α'), (16O, 16O'), other (n,n'), and charge distribution measurements is presented and discussed. It is emphasized that for these N=Z nuclei the quadrupole deformations and deformation lengths are in very good agreement when measured through neutron and proton scattering as well as electromagnetic excitations.
    Physical Review C 12/1984; 30(6):1795-1809. · 3.72 Impact Factor
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    ABSTRACT: Differential cross sections for neutron elastic and inelastic scattering from the actinide nuclei /sup 232/Th, /sup 233/U, /sup 235/U, /sup 238/U, /sup 239/Pu, and /sup 242/Pu have been measured at incident energies ranging from 0.6 to 3.4 MeV using a multiangle time-of-flight spectrometer. The energy resolution of the spectrometer was high enough to experimentally resolve the elastic and first inelastic groups for /sup 232/Th, /sup 233/U, /sup 238/U, and /sup 242/Pu at all energies. Cross section for groups of states have been obtained for /sup 235/U and /sup 239/Pu. Comparison of these measurements with evaluations in the latest evaluated data files shows substantial discrepancies, particularly at high energies. The present results for /sup 232/Th, /sup 235/U, /sup 238/U, and /sup 239/Pu have been combined with total cross-section measurements and low-energy scattering properties in an analysis based on the coupled-channel and compound-nucleus formalisms. Optical potential parameters and nuclear deformations have been derived and are discussed.
    Nucl. Sci. Eng. 08/1982;
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    ABSTRACT: The energy balance in the fission of 234U has been investigated on the basis of experimental results from the 233U(d,pf) reaction. Taking into account the neutron evaporation we have deduced the total kinetic energy and excitation energy distributions of the primary fragments as functions of the excitation energy of the fissioning nucleus. The neutron evaporation temperatures have been adjusted so as to reproduce the average value and width of the measured kinetic energy distributions for each fragmentation. Excitation energy distributions of the fragments have been deduced. The data are discussed in the framework of the liquid drop model with shell corrections. Evidence for energy dissipation in the fission of 234U, involving drastic changes in the scission configuration, is shown for some fragmentation modes.
    01/1982;
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    ABSTRACT: The energy balance in the fission of 234U has been investigated on the basis of experimental results from the 233U(d, pf) reaction. Taking into account the neutron evaporation we have deduced the total kinetic energy and excitation energy distributions of the primary fragments as functions of the excitation energy of the fissioning nucleus. The neutron evaporation temperatures have been adjusted so as to reproduce the average value and width of the measured kinetic energy distributions for each fragmentation. Excitation energy distributions of the fragments have been deduced. The data are discussed in the framework of the liquid-drop model with shell corrections. Evidence for energy dissipation in the fission of 234U, involving drastic changes in the scission configuration, is shown for some fragmentation modes.
    Nuclear Physics A 01/1982; · 2.50 Impact Factor
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    ABSTRACT: Differential cross sections for neutron scattering from the 182,183,184,186W isotopes have been measured at an incident energy of 3.4 MeV. Angular distributions have been obtained for elastic scattering and inelastic scattering to the first and second excited levels of the four isotopes. Nuclear deformations have been extracted for these nuclei from a coherent analysis which combines the data presented here with low energy neutron scattering properties and total cross sections over a wide energy range. The coupled-channel and compound nucleus formalisms were used in this analysis. Volume integrals and root mean square radii of the obtained neutron optical model potential are presented and compared to the theoretical predictions of Jeukenne, Lejeune, and Mahaux. In addition, the quadrupole and hexadecapole moments of our potential are compared to the potential moments deduced from deuteron and alpha-particle scattering measurements and to experimental charge distribution moments. Finally, matter rms radii have been estimated for the four isotopes and are compared with new Hartree-Fock-Bogolyubov calculations involving Gogny's D1 effective force.NUCLEAR REACTIONS 182,183,184,186W(n,n), (n,n′), En=3.40 MeV; measured σ(En,θ), θ=20-160°. Coupled-channel and statistical model calculations. Deduced optical potential parameters, deformation parameters, potential moments, volume integrals, and rms radii. Estimated rms matter radii.
    Physical Review C 01/1981; 23(1). · 3.72 Impact Factor
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    ABSTRACT: Differential cross sections for neutron elastic and inelastic scattering from 232Th, 233U, 235U, 238U, 239Pu, and242Pu were measured at incident energies ranging from 0.6 to 3.4 MeV. Comparison of these results with the latest available evaluations show large discrepancies. The data were analyzed in the framework of the direct interaction and compound nucleus formalisms. Optical potential parameters and nuclear deformation parameters deduced from the calculations are discussed.
    01/1981;
  • 09/1980;
  • 09/1980;
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    ABSTRACT: Deformation effects in differential cross sections for neutron scattering from 142,144,146,148,150Nd have been studied at an incident energy of 7 MeV, where measurements and calculations of total cross sections show maximum differences for different deformations. Differential cross sections were obtained for elastic scattering and inelastic scattering to the first 2+ states of the five isotopes. The experimental cross sections are compared to the predictions of surface excitation models using coupled-channels calculations. The parameters of the model are adjusted to fit low energy scattering properties and total cross sections for incident energies from 0.7 to 14 MeV as well as the present data. The large set of data tightly constrains all parameters, including the quadrupole deformation parameters. These are compared to those obtained using other probes of the nuclear surface. NUCLEAR REACTIONS 142, 144, 146, 148, 150Nd(n,n), (n,n'), En=7.0 MeV measured σ(En,θ) θ=20-160° Δθ=5°. Enriched targets. Deduced coupled-channels optical potential parameters, quadrupole deformation parameters.
    Physical Review C 07/1979; 20(1):78-87. · 3.72 Impact Factor
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    ABSTRACT: A new experimental method is proposed to determine, as a function of excitation energy of the fissioning nucleus, the mass and energy distributions of the fragments for both pre- and post-neutron emission. From these distributions also the average number of neutrons emitted by the fission fragments as a function of initial fragment masses can be derived. The method is based on the measurement of both fragment kinetic energies and velocities in charged-particle induced fission through reactions such as (d, p⨍) where the emitted charged particle is used as starting time for the fragment velocity determination. The major interest lies in the precision of about 0.5 amu in the pre-neutron mass determination. Details of the experimental arragement and the method of data analysis are given. Typical experimental results obtained from the 233U(d, p⨍) reaction are shown and compared with previously reported results.
    Nuclear Instruments and Methods 04/1979; 160(3):471-485.
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    ABSTRACT: Measurements of differential cross sections for fast neutrons scattered by carbon are presented for 14 incident neutron energies between 8.0 and 14.5 MeV. The measurements were performed with the four-detector neutron time-of-flight facility of the Centre d'Etudes de Bruyeres-le-Chatel tandem Van de Graaff accelerator. The angular distributions for elastic and inelastic scattering to the first excited level of /sup 12/C were obtained over the angular range from 10 to 160/sup 0/. The experimental uncertainties vary from 7 to 15% for the differential elastic scattering cross sections and from 8 to 22% for the differential inelastic scattering cross sections. These measurements partially fill in an energy range that was previously characterized by a lack of data. The angle-integrated cross sections are compared to the evaluated values of ENDF/B, and significant discrepancies are shown. The present data were included in an evaluation work on carbon carried out in this laboratory. The consistency of total cross-section measurements with our data and other partial cross sections is discussed.
    Nucl. Sci. Eng.; (United States). 01/1978; 65:2.
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    ABSTRACT: Three resonances in 12C + 12C with Ec.m.(Jpi) of 8.85(6+), 11.2(8+), and 13.75(10+) are reported. Together with earlier data, these resonances fit in a rotational band in 24Mg. A model based on the rotation-vibration coupling is proposed to account for these data.
    Physical Review Letters 01/1977; 39(18):1135-1138. · 7.73 Impact Factor
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    ABSTRACT: Differential cross sections for elastic scattering from the even-A isotopes of Se have been measured at 6, 8, and 10 MeV. Inelastic scattering differential cross sections have been obtained at 6- and 8-MeV incident energies. The results have been analyzed in a coupled channel model to determine the isospin coefficients in the real and imaginary parts of the scattering potential and the deformation parameters ..beta../sub 2/ appropriate to neutron scattering in these vibrational nuclei. Both the coupling to the first 2/sup +/ level and the imaginary scattering potential vary strongly between /sup 76/Se and /sup 82/Se, and in such a way that their effects cancel each other for inelastic scattering. It is shown that with an adequate data set the strong coupling and isospin dependencies of neutron scattering can be separated. The normalization uncertainty of these measurements is about 7%, and the statistical precision ranges from 1 to 10%. (AIP)
    Physical Review C 09/1976; 14(3). · 3.72 Impact Factor
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    ABSTRACT: Differential elastic and inelastic cross sections for fast neutrons scattered by carbon have been measured between 8.0 and 14.5 MeV. No other results on /sup 12/C seem to have been reported, at this time, between 9 and 14 MeV. A complete and consistent set of data for carbon, including total, elastic and inelastic, (n,..cap alpha..) and (n,n'3..cap alpha..) cross sections, is now available for energies below 14.5 MeV. 4 figures (auth)
    09/1975
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    J. Lachkar, Y. Patin, J. Sigaud
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    ABSTRACT: The variations of kinetic and excitation energies and fragment masses from the (d, pf) and (n, f) reactions have been studied as a function of the excitation energy of 240Pu. These results have been analyzed together with those from spontaneous and isomeric fission reported elsewhere. They tend to illustrate the existence of two modes of fission ; the first one is superfluid, the other is strongly damped in the last stage of the fission process. Les variations de l'énergie cinétique, de l'énergie d'excitation et des masses des fragments, grandeurs caractéristiques de la fission, ont été étudiées en fonction de l'énergie d'excitation, dans le cas de 240Pu, à partir des réactions (d, pf) et (n, f). Ces résultats sont analysés avec ceux de la fission spontanée et de la fission isomérique, rapportés par ailleurs. Ils tendent à illustrer l'existence de deux modes de fission, le premier superfluide, le second caractérisé par un fort amortissement après la traversée de la barrière.
    http://dx.doi.org/10.1051/jphyslet:0197500360407900. 01/1975;
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    ABSTRACT: The energy levels of 56Fe have been studied by means of the (p, p′γ) and (n, n′γ) reactions. Particle-gamma coincidences from the 56Fe(p, p′γ) reaction have been measured at 6.5, 8, 10 and 11 MeV incident proton energies. The coincident γ-rays were detected with a 100 cm3 Ge(Li) detector and protons with cooled Si(Li) diodes. Independently, absolute differential cross sections for the production of γ-rays by inelastic neutron scattering from iron have been measured in the energy range 4.8–8.8 MeV. A 65 cm3 Ge(Li) detector surrounded by a NaI (Tl) annulus and associated with a pulsed beam time-of-flight system was used to detect the deexcitation γ-rays. By comparing the measured angular distributions and excitation functions with those calculated on the basis of the statistical theory, spin assignments for poorly known states are made. From these two experiments, a decay scheme is constructed and proposed. The results are briefly compared with mixed-configuration shell model calculations.
    Nuclear Physics A 04/1974; · 2.50 Impact Factor