R. Dayras

Publications (186)93.67 Total impact

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  Available from: C. Beck

  Dataset: ZeitPhys

  C. Beck, B. Djerroud, B. Heusch, R. Dayras, R. M. Freeman, F. Haas, A. Hachem, J. P. Wieleczko, M. Youlal
• Article: Correlations between emission timescale of fragments and isospin dynamics in $^{124}$Sn+$^{64}$Ni and $^{112}$Sn+$^{58}$Ni reactions at 35 AMeV

  E. De Filippo, A. Pagano, P. Russotto, F. Amorini, A. Anzalone, L. Auditore, V. Baran, I. Berceanu, B. Borderie, R. Bougault, [......], K. Siwek-Wilczynska, I. Skwira-Chalot, A. Trifirò, M. Trimarchi, G. Verde, M. Vigilante, J. P. Wieleczko, J. Wilczynski, L. Zetta, W. Zipper
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  ABSTRACT: We present a new experimental method to correlate the isotopic composition of intermediate mass fragments (IMF) emitted at mid-rapidity in semi-peripheral collisions with the emission timescale: IMFs emitted in the early stage of the reaction show larger values of $<$N/Z$>$ isospin asymmetry, stronger angular anisotropies and reduced odd-even staggering effects in neutron to proton ratio $<$N/Z$>$ distributions than those produced in sequential statistical emission. All these effects support the concept of isospin "migration", that is sensitive to the density gradient between participant and quasi-spectator nuclear matter, in the so called neck fragmentation mechanism. By comparing the data to a Stochastic Mean Field (SMF) simulation we show that this method gives valuable constraints on the symmetry energy term of nuclear equation of state at subsaturation densities. An indication emerges for a linear density dependence of the symmetry energy.
  06/2012;
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  Available from: C. Beck

  Article: Asymmetric Fission in the 78Kr+40Ca reactions at 5.5 MeV/nucleon

  DOI J P Wieleczko, G Ademard, K Mazurek, C Schmitt, E Bonnet, A Chbihi, J D Frankland, J Gomez del Campo, M La Commara, M Vigilante, [......], G De Angelis, J De Sanctis, V L Kravchuk, P Lautesse, N Le Neindre, A D’Onofrio, M Parlog, D Pierroutsakou, M Romoli, R Roy
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  ABSTRACT: The cross section, kinetic energy distribution and angular distribution of fragments with atomic number 3 ≤ Z ≤ 28 emitted in the reaction 78Kr + 40Ca at the bombarding energy of 5.5 MeV/nucleon and coincidence between light charged particles and fragments were measured by means of the 4π-INDRA array to study the decay mechanism of medium mass excited nucleus. Global features indicate a high degree of relaxation and are compatible with a binary fission from compound nucleus. The mean value of the kinetic energy distributions of fragments indicates dominance of Coulomb interaction, while the width of the distribution signals large fluctuations. Inclusive cross-section distributions of fragments with charge 3 ≤ Z ≤ 28 are bell-shaped and a strong even-odd-staggering (o-es) is observed for 3 ≤ Z ≤ 12. Coincidence measurements suggest that the light partners in very asymmetric fission are emitted at excitation energies below the particle emission thresholds. Data were confronted to the predictions of statistical model describing the decay of compound nuclei by emission of light particles and fragments. Calculations assuming spherical fission fragments and finite-range liquid drop fission barriers are not able to explain the experimental features. Attempts have been made to improve the agreement with experimental data. The analysis indicates the strong influence of the shape parameterization of the potential energy surface in describing the fission process of intermediate mass compound nuclei.
  The European Physical Journal Conferences 01/2012; 21:02001.
• Article: Correlations between emission timescale of fragments and isospin dynamics in Sn-124+Ni-64 and Sn-112+Ni-58 reactions at 35A MeV

  E De Filippo, A Pagano, P Russotto, F Amorini, A Anzalone, L Auditore, V Baran, I Berceanu, B Borderie, R Bougault, [......], K Siwek-Wilczynska, I Skwira-Chalot, A Trifiro, M Trimarchi, G Verde, M Vigilante, J P Wieleczko, J Wilczynski, L Zetta, W Zipper
  Physical Review C. 01/2012; 86(1).
• Source

  Available from: Karl Hauschild

  Article: Study of $^{124}$Sn+$^{136}$Xe fusion-evaporation: analysis of a rare-event experiment

  Benoît Avez, Antoine Drouart, Ch. Stodel, Cédric Simenel, J. Alcantara, M. Adamczyk, P. Banka, E. Bonnet, E. Clément, R. Dayras, [......], A. Popeko, T. Roger, M G Saint-Laurent, Z. Sosin, B. Sulignano, C. Theisen, A. Wieloch, A. Yeremin, B. Yilmaz, M. Zielinska
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  ABSTRACT: Fusion-evaporation in the $^{124}$Sn+$^{136}$Xe system is studied using a high intensity xenon beam provided by the Ganil accelerator and the LISE3 wien filter for the selection of the products. Due to the mass symmetry of the entrance system, the rejection of the beam by the spectrometer was of the order of $5times10^8$. We have thus performed a detailed statistical analysis to estimate random events and to infer the fusion-evaporation cross sections. No signicant decay events were detected and upper limit cross sections of 172 pb, 87 pb and 235 pb were deduced for the synthesis of $^{257}$Rf, $^{258}$Rf and $^{259}$Rf, respectively.
  11/2011;
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  Available from: Abdou Chbihi

  Article: Decay of excited nuclei produced in $^{78,82}$Kr + $^{40}$Ca reactions at 5.5 MeV/nucleon

  G. Ademard, J. P. Wieleczko, J. Gomez del Campo, M. La Commara, E. Bonnet, M. Vigilante, A. Chbihi, J. D. Frankland, E. Rosato, G. Spadaccini, [......], N. Le Neindre, J. Moisan, A. D'Onofrio, M. Parlog, D. Pierroutsakou, M. F. Rivet, M. Romoli, R Roy, G. G. Adamian, N. V. Antonenko
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  ABSTRACT: Decay modes of excited nuclei are investigated in $^{78,82}$Kr + $^{40}$Ca reactions at 5.5 MeV/nucleon. Charged products were measured by means of the $4\pi$ INDRA array. Kinetic-energy spectra and angular distributions of fragments with atomic number 3 $\le Z \le$ 28 indicate a high degree of relaxation and are compatible with a fission-like phenomenon. Persistence of structure effects is evidenced from elemental cross-sections ($\sigma_{Z}$) as well as a strong odd-even-staggering (o-e-s) of the light-fragment yields. The magnitude of the staggering does not significantly depend on the neutron content of the emitting system. Fragment-particle coincidences suggest that the light partners in very asymmetric fission are emitted either cold or at excitation energies below the particle emission thresholds. The evaporation residue cross-section of the $^{78}$Kr + $^{40}$Ca reaction is slightly higher than the one measured in $^{82}$Kr + $^{40}$Ca reaction. The fission-like component is larger by $\sim$ 25% for the reaction having the lowest neutron-to-proton ratio. These experimental features are confronted to the predictions of theoretical models. The Hauser-Feshbach approach including the emission of fragments up to $Z$ = 14 in their ground states as well as excited states does not account for the main features of $\sigma_{Z}$. For both reactions, the transition-state formalism reasonably reproduces the $Z$-distribution of the fragments with charge 12 $\le Z \le$ 28. However, this model strongly overestimates the light-fragment cross-sections and does not explain the o-e-s of the yields for 6 $\le Z \le$ 10. The shape of the whole $Z$-distribution and the o-e-s of the light-fragment yields are satisfactorily reproduced within the dinuclear system framework which treats the competition between evaporation, fusion-fission and quasifission processes. The model suggests that heavy fragments come mainly from quasifission while light fragments are predominantly populated by fusion. An underestimation of the cross sections for 16 $\le Z \le$ 22 could signal a mechanism in addition to the capture process.
  04/2011;
• Article: Strong enhancement of dynamical emission of heavy fragments in the neutron-rich 124Sn+64Ni reaction at 35A MeV

  P. Russotto, E. De Filippo, A. Pagano, E. Piasecki, F. Amorini, A. Anzalone, L. Auditore, V. Baran, I. Berceanu, J. Blicharska, [......], K. Schmidt, K. Siwek-Wilczyńska, I. Skwira-Chalot, A. Trifirò, M. Trimarchi, M. Vigilante, J. P. Wieleczko, J. Wilczyński, L. Zetta, W. Zipper
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  ABSTRACT: A quantitative comparison is made between the absolute cross sections associated with statistical and dynamical emission of heavy fragments in the 124Sn+64Ni and 112Sn+58Ni collisions experimentally investigated at 35A MeV beam energy using the multidetector CHIMERA. The result shows that the dynamical process is about twice as probable in the neutron-rich 124Sn+64Ni system as in the 112Sn+58Ni neutron-poor one. This unexpected and significant difference indicates that the reaction mechanism is strongly dependent on the entrance-channel isospin (N/Z) content.
  Phys. Rev. C. 06/2010; 81(6).
• Source

  Available from: Abdou Chbihi

  Article: The prominent role of the heaviest fragment in multifragmentation and phase transition for hot nuclei

  Bernard Borderie, E. Bonnet, N. Le Neindre, S. Piantelli, Ad. R. Raduta, M. F. Rivet, E. Galichet, F. Gulminelli, D. Mercier, B. Tamain, [......], A. Chbihi, J. P. Wieleczko, D. Guinet, P. Lautesse, F. Gagnon-Moisan, R Roy, M. Vigilante, E. Rosato, R. Dayras, J. Lukasik
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  ABSTRACT: The role played by the heaviest fragment in partitions of multifragmenting hot nuclei is emphasized. Its size/charge distribution (mean value, fluctuations and shape) gives information on properties of fragmenting nuclei and on the associated phase transition.
  03/2010;
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  Available from: Abdou Chbihi

  Article: Isospin Diffusion in $^{58}$Ni-Induced Reactions at Intermediate Energies

  E. Galichet, Marie-France Rivet, B. Borderie, M Colonna, R. Bougault, D. Durand, N. Le Neindre, O. Lopez, L. Manduci, E. Vient, A. Chbihi, J. D. Frankland, J. P. Wieleczko, R. Dayras, C. Volant, D. C. R. Guinet, P. Lautesse, M. Parlog, E. Rosato, M. Vigilante
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  ABSTRACT: Isospin diffusion is probed as a function of the dissipated energy by studying two systems $^{58}$Ni+$^{58}$Ni and $^{58}$Ni+$^{197}$Au, over the incident energy range 52-74\AM. Experimental data are compared with the results of a microscopic transport model with two different parameterizations of the symmetry energy term. A better overall agreement between data and simulations is obtained when using a symmetry term with a potential part linearly increasing with nuclear density. The isospin equilibration time at 52 \AM{} is estimated to 130$\pm$10 fm/$c$.
  03/2010;
• Article: Multifragmentation and phase transition for hot nuclei: recent progress

  B. Borderie, E. Bonnet, F. Gulminelli, N. Le Neindre, D. Mercier, S. Piantelli, Ad.R. Raduta, M.F. Rivet, B. Tamain, R. Bougault, [......], E. Galichet, F. Gagnon-Moisan, D. Guinet, P. Lautesse, J. Lukasik, M. Pârlog, E. Rosato, R. Roy, M. Vigilante, J.P. Wieleczko
  Nuclear Physics A 03/2010; 834:535. · 1.54 Impact Factor
• Article: Influence Of The Neutron Richness On Binary Decays

  G. Ademard, J. P. Wieleczko, E. Bonnet, A. Chbihi, J. D. Frankland, La Commara M, M. Vigilante, E. Rosato, A. D’Onofrio, G. Spadaccini, [......], A. Galindo-Uribarri, P. Lautesse, Le Neindre N, M. Parlog, D. Pierroutsakou, F. Rejmund, M. F. Rivet, M. Romoli, R Roy, D. Shapira
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  ABSTRACT: The influence of the neutron richness on binary decays is investigated in 78,82Kr+ 40Ca reactions at 5.5 MeV/A incident energy. Kinetic energy distributions and angular distributions of fragments with atomic number 6 ≤ Z ≤ 28 were measured using the 4π-INDRA array. Global features are compatible with an emission from a long-lived system. The yields around the symmetric splitting are about 30The persistence of strong structural effects is evidenced from elemental cross-sections of the light fragments. The cross-sections for odd-Z fragments are higher for the neutron rich CN while cross-sections for even-Z fragments are higher for the neutron poor CN. Calculations assuming two different potential energy surfaces are presented.
  EPJ Web of Conferences. 01/2010;
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  Available from: J. Lukasik

  Article: Bimodal behavior of the heaviest fragment distribution in projectile fragmentation.

  E Bonnet, D Mercier, B Borderie, F Gulminelli, M F Rivet, B Tamain, R Bougault, A Chbihi, R Dayras, J D Frankland, [......], D Guinet, P Lautesse, J Lukasik, N Le Neindre, M Pârlog, E Rosato, R Roy, M Vigilante, J P Wieleczko, B Zwieglinski
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  ABSTRACT: The charge distribution of the heaviest fragment detected in the decay of quasiprojectiles produced in intermediate energy heavy-ion collisions has been observed to be bimodal. This feature is expected as a generic signal of phase transition in nonextensive systems. In this Letter, we present new analyses of experimental data from Au on Au collisions at 60, 80, and 100 MeV/nucleon showing that bimodality is largely independent of the data selection procedure and of entrance channel effects. An estimate of the latent heat of the transition is extracted.
  Physical Review Letters 08/2009; 103(7):072701. · 7.37 Impact Factor
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  Available from: D. Guinet

  Article: Isospin diffusion in^{58} Ni-induced reactions at intermediate energies. I. Experimental results

  E. Galichet, M. F. Rivet, B. Borderie, M. Colonna, R. Bougault, A. Chbihi, R. Dayras, D. Durand, J. D. Frankland, D. C. R. Guinet, P. Lautesse, N. Le Neindre, O. Lopez, L. Manduci, M. Pârlog, E. Rosato, B. Tamain, E. Vient, C. Volant, J. P. Wieleczko
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  ABSTRACT: Isospin diffusion in semiperipheral collisions is probed as a function of the dissipated energy by studying two systems 58Ni+58Ni and 58Ni+197Au, over the incident energy range 52A-74A MeV. A close examination of the multiplicities of light products in the forward part of the phase space clearly shows an influence of the isospin of the target on the neutron richness of these products. A progressive isospin diffusion is observed when collisions become more central, in connection with the interaction time.
  Phys. Rev. C. 06/2009; 79(6).
• Article: Dynamical Signals in Fragmentation Reactions: Time Scale Determination from Three Fragments Correlations by Using the 4pi CHIMERA Multidetector

  E. de Filippo, F. Amorini, A. Anzalone, L. Auditore, V. Baran, I. Berceanu, J. Blicharska, B. Borderie, R. Bougault, M. Bruno, [......], I. Skwira, A. Sochocka, A. Trifirň, M. Trimarchi, G. Verde, M. Vigilante, J. P. Wieleczko, J. Wilczyński, L. Zetta, W. Zipper
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  ABSTRACT: For fragments emitted in the reactions 124Sn + 64Ni and 112Sn + 58Ni at 35 AMeV, isotopic composition and velocity correlations have been studied as a function of the centrality of the collision, using the 4pi Chimera multidetector. We have investigated the time scale for fragments formation, in order to distinguish between prompt dynamical and sequential statistical emission. Promptly emitted light fragments (Z leq 9) produced in the mid-rapidity domain are characterised by larger N/Z ratio and stronger angular anisotropies than those produced in sequential statistical emission. Results are compared with stochastic BNV code simulations obtained for primary fragments. Valuable information on the symmetry term of the nuclear equation of state at sub-saturation densities are obtained.
  Acta Physica Polonica Series B 03/2009; 40:1199. · 0.90 Impact Factor
• Article: N/Z Influence on Disintegration Modes of Compound Nuclei

  J. P. Wieleczko, E. Bonnet, J. Gomez Del Campo, M. La Commara, M. Vigilante, J. D. Frankland, A. Chbihi, E. Rosato, A. Galindo-Uribarri, D. Shapira, [......], N. Le Neindre, L. Nalpas, A. D. Onofrio, M. Parlog, D. Pierroutsakou, F. Rejmund, M. F. Rivet, M. Romoli, R. Roy, B. Tamain
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  ABSTRACT: Investigations on the influence of the neutron enrichment on the decay channels of excited nuclei are presented. Characteristics of fragments with charge 6 le Z le 28 emitted in 78,82{Kr}+40Ca at 5.5 MeV/A reactions were measured at the GANIL facility. Data are compatible with an emission process from compound nucleus and are discussed in the framework of the transition state model.
  Acta Physica Polonica Series B 02/2009; 40:577. · 0.90 Impact Factor
• Chapter: Isospin Effects In Projectile-like Dynamical Fission For (112,124)Sn+(58,64)Ni Reactions At 35 AMeV

  P Russotto, E De Filippo, A Pagano, E Piasecki, F Amorini, A Anzalone, L Auditore, V Baran, I Berceanu, J Blicharska, [......], I Skwira-Chalot, A Sochocka, L Swiderski, A Trifiro, M Trimarchi, M Vigilante, J P Wieleczko, J Wilczynski, L Zetta, W Zipper
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  ABSTRACT: A quantitative comparison regarding absolute cross sections associated to Statistical and Dynamical Fission processes in the (124)Sn+(64)Ni and (112)Sn+(58)Ni collisions experimentally investigated at 35 AMeV beam energy using multi-detector CHIMERA is presented. It results that Dynamical Fission process is about two times more probable in the neutron rich (124)Sn+(64)Ni system than in the (112)Sn+(58)Ni neutron poor one. The observed difference could indicate an influence of the entrance channel Isospin (N/Z) content on the reaction mechanisms.
  01/2009: pages 389-392;
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  Available from: Paolo Napolitani

  Article: Multi-particle correlation function to study short-lived nuclei

  F. Grenier, A. Chbihi, R Roy, G. Verde, D. Thériault, J. D. Frankland, J. P. Wieleczko, B. Borderie, R. Bougault, R. Dayras, [......], O. Lopez, J. Moisan, L. Nalpas, P. Napolitani, M. Parlog, M. F. Rivet, E. Rosato, B. Tamain, E. Vient, M. Vigilante
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  ABSTRACT: Unstable 10C nuclei are produced as quasi-projectiles in 12C+24Mg collisions at E/A = 53 and 95 MeV. The decay of their short-lived states is studied with the INDRA multidetector array via multi-particle correlation functions. The obtained results show that heavy-ion collisions can be used as a tool to access spectroscopic information of unbound states in exotic nuclei, such as their energies and the relative importance of different sequential decay widths.
  11/2008;
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  Available from: Cédric Ray

  Article: Fission time measurements: a new probe into superheavy element stability.

  M Morjean, D Jacquet, J L Charvet, A L'Hoir, M Laget, M Parlog, A Chbihi, M Chevallier, C Cohen, D Dauvergne, [......], J D Frankland, R Kirsch, P Lautesse, L Nalpas, C Ray, C Schmitt, C Stodel, L Tassan-Got, E Testa, C Volant
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  ABSTRACT: Reaction mechanism analyses performed with a 4pi detector for the systems 208Pb + Ge, 238U + Ni and 238U + Ge, combined with analyses of the associated reaction time distributions, provide us with evidence for nuclei with Z=120 and 124 living longer than 10(-18) s and arising from highly excited compound nuclei. By contrast, the neutron deficient nuclei with Z=114 possibly formed in 208Pb + Ge reactions have shorter lifetimes, close to or below the sensitivity limit of the experiment.
  Physical Review Letters 09/2008; 101(7):072701. · 7.37 Impact Factor
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  Available from: C. Beck

  Article: Influence of Neutron Enrichment on Disintegration Modes of Compound Nuclei

  E. Bonnet, J. P. Wieleczko, A. Chbihi, J. D. Frankland, J. Moisan, F. Rejmund, J. Gomez del Campo, A. Galindo-Uribarri, D. Shapira, M. La Commara, [......], B. Borderie, M. F. Rivet, R. Dayras, L. Nalpas, G De Angelis, T. Glodariou, V. Kravchuk, Ph. Lautesse, A. D’Onofrio, R Roy
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  ABSTRACT: Cross sections, kinetic energy and angular distributions of fragments with charge 6$\le$Z$\le$28 emitted in 78,82Kr+40C at 5.5 MeV/A reactions were measured at the GANIL facility using the INDRA apparatus. This experiment aims to investigate the influence of the neutron enrichment on the decay mechanism of excited nuclei. Data are discussed in comparison with predictions of transition state and Hauser-Feshbach models. Comment: 8 pages, 1 figure, paper presented at the First Workshop on "State of the Art in Nuclear Cluster Physics" 13-16 May, 2008, at Strasbourg, France (SOTANCP2008) and accepted for publication at International Journal of Modern Physics E (Special Issue), Proceedings of SOTANCP2008 (to be published)
  08/2008;
• Article: Long Fission Times of Super‐Heavy Compound Nuclei

  A. Drouart, J. L. Charvet, A. Chbihi, M. Chevallier, C. Cohen, D. Dauvergne, R. Dayras, J. D. Frankland, D. Jacquet, R. Kirsch, [......], A. L'Hoir, A. Marchix, M. Morjean, L. Nalpas, M. Parlog, C. Ray, C. Schmitt, C. Stodel, L. Tassan‐Got, C. Volant
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  ABSTRACT: The blocking technique in single crystals is a direct method to investigate the presence of long fission time components. With a lead beam impinging on a germanium single crystal, we tried to produce compound nuclei (CN) with atomic number Z = 114 at high excitation energy. Blocking patterns for reaction products are reconstructed with position sensitive detectors at 20 ° relative to the beam direction. The Z and the energies of all products are measured with ΔE‐E telescopes of the 4π INDRA array, so that all reaction channels are unambiguously identified. With this setup, we can reach long fission times (>10−18 s) that can be associated with CN fissions. However, in contrast to previous experiments in which such long fission times could be measured for Z = 120 and 124, no hint of long lifetimes within our sensitivity limit for Z = 114 was observed, which may be due to the neutron deficiency of the formed isotopes.
  AIP Conference Proceedings. 04/2008; 1005(1):215-218.