Quantum microscopic approach to low-energy heavy ion collisions

The Time-dependent Hartree-Fock (TDHF) theory is applied to the study of heavy ion collisions at energies around the Coulomb barrier. The competition between fusion and nucleon transfer mechanisms is investigated. For intermediate mass systems such as 16O+208Pb, proton transfer favors fusion by reducing the Coulomb repulsion. A comparison with sub-barrier transfer experimental data shows that pairing correlations are playing an important role in enhancing proton pair transfer. For heavier and more symmetric systems, a fusion hindrance is observed due to the dominance of the quasi-fission process. Typical quasi-fission time of few zeptoseconds are obtained. Actinide collisions are also investigated both within the TDHF approach and with the Ballian-V\'en\'eroni prescription for fluctuation and correlation of one-body observables. The possible formation of new heavy neutron-rich nuclei in actinide collisions is discussed.Comment: Invited Plenary Talk given at NN201

Microscopic approaches for nuclear Many-Body dynamics: applications to nuclear reactions

These lecture notes are addressed to PhD student and/or researchers who want a general overview of microscopic approaches based on mean-field and applied to nuclear dynamics. Our goal is to provide a good description of low energy heavy-ion collisions. We present both formal aspects and practical applications of the time-dependent Hartree-Fock (TDHF) theory. The TDHF approach gives a mean field dynamics of the system under the assumption that particles evolve independently in their self-consistent average field. As an example, we study the fusion of both spherical and deformed nuclei with TDHF. We also focus on nucleon transfer which may occur between nuclei below the barrier. These studies allow us to specify the range of applications of TDHF in one hand, and, on the other hand, its intrinsic limitations: absence of tunneling below the Coulomb barrier, missing dissipative effects and/or quantum fluctuations. Time-dependent mean-field theories should be improved to properly account for these effects. Several approaches, generically named "beyond TDHF" are presented which account for instance for pairing and/or direct nucleon-nucleon collisions. Finally we discuss recent progresses in exact ab-initio methods based on the stochastic mean-field concept.Comment: 55 pages. Lecture given at the "Joliot Curie" school, Maubuisson, september 17-22, 2007. A french version is available at http://www.cenbg.in2p3.fr/heberge/EcoleJoliotCurie/coursannee/cours/CoursSimenel.pd

Time-Depentent Hartree-Fock description of heavy ions fusion

7 pages, 5 figures, Contribution to XIV Nuclear Physics Workshop at Kazimierz Dolny, Poland, Sept. 26-29, 2007International audienceA microscopic mean-field description of heavy ions fusion is performed in the framework of the Time-Dependent Hartree-Fock (TDHF) theory using a Skyrme interaction with the SLy4d parametrization. A good agreement with experiments is obtained on the position of the fusion barriers for various total masses, mass asymmetries and deformations. The excitation function of the 16O+208Pb is overestimated by about 16% above the barrier. The restriction to an independent particles state in the mean-field dynamics prevents the description of sub-barrier fusion. Effect of transfer on fusion is discussed

Microscopic description of heavy ion collisions around the barrier

7 pages, 9 figuresInternational audienceA microscopic mean-field description of heavy ion collisions is performed in the framework of the time dependent Hartree-Fock theory using a Skyrme energy density functional. A good agreement with experiments is obtained on the position of the fusion barriers for various total masses and mass asymmetries. The excitation function of the 16O+208Pb is overestimated by about 16% above the barrier. Transfer below the barrier is studied in 16O+208Pb central collisions. Heavier systems are considered to study their fusion hindrance. We also compute collision times of the 238U+238U system. The latter has been used to produce super strong electric fields and to test non perturbative quantum electrodynamics theory. Indeed, if the life time of such giant system is of the order of few 10^-21 s, its electric field should induce spontaneous electron-positron pair emissions from vacuum. In our calculations, highest collision times are reached in the 238U+238U reaction for center of mass energies between 1000 and 1300 MeV

Effects of Nuclear Structure on Quasi-fission

The quasi-fission mechanism hinders fusion of heavy systems because of a mass flow between the reactants, leading to a re-separation of more symmetric fragments in the exit channel. A good understanding of the competition between fusion and quasi-fission mechanisms is expected to be of great help to optimize the formation and study of heavy and superheavy nuclei. Quantum microscopic models, such as the time-dependent Hartree-Fock approach, allow for a treatment of all degrees of freedom associated to the dynamics of each nucleon. This provides a description of the complex reaction mechanisms, such as quasi-fission, with no parameter adjusted on reaction mechanisms. In particular, the role of the deformation and orientation of a heavy target, as well as the entrance channel magicity and isospin are investigated with theoretical and experimental approaches.Comment: Invited talk to NSRT12. To be published in Eur. Phys. J. Web of Con

: Gender differences in STEMI

International audienceBACKGROUND: Gender differences in presentation, management and outcome in patients with ST-segment elevation myocardial infarction (STEMI) have been reported. AIM: To determine whether female gender is associated with higher inhospital mortality. METHODS: Data from ORBI, a regional STEMI registry of 5 years' standing, were analysed. The main data on presentation, management, inhospital outcome and prescription at discharge were compared between genders. Various adjusted hazard ratios were then calculated for inhospital mortality (women versus men). RESULTS: The analysis included 5000 patients (mean age 62.6±13 years), with 1174 women (23.5%). Women were on average 8 years older than men, with more frequent co-morbidities. Median ischaemia time was 215 minutes (26 minutes longer in women; P<0.05). Reperfusion strategies in women less frequently involved fibrinolysis, coronary angiography, radial access and thrombo-aspiration. Female gender, especially in patients aged<60 years, was associated with poorer inhospital prognosis (including higher inhospital mortality: 9% vs. 4% in men; P<0.0001), and underutilization of recommended treatments at discharge. Moreover, excess female inhospital mortality was independent of presentation, revascularization time and reperfusion strategy (hazard ratio for women 1.33, 95% confidence interval 1.01-1.76; P=0.04). CONCLUSIONS: One in four patients admitted for STEMI was female, with significant differences in presentation. Female gender was associated with less-optimal treatment, both in the acute-phase and at discharge. Efforts should be made to reduce these differences, especially as female gender was independently associated with an elevated risk of inhospital mortality

Mouvements collectifs dans les noyaux : des vibrations à la fusion

This manuscript is devoted to the study of collective behaviors encountered in nuclear physics. The time dependent energy density functional method (TDEDF) is one of the most achieved model for such studies. One of the first implementation of TDEDF formalism treating pairing correlation (through the resolution of the time dependent Hartree-Fock-Bogoliubov equations) is presented. In a second part, we apply the TDEDF formalism to the study of some collective excitations. First, we focus on the study of structure and decay properties of the giant monopole resonance in some closed shells nuclei. The study of another type of excitation of the atomic nucleus is also investigated : the pairing vibrations. The impact of different energy density functionals is discussed. The third part of this work is devoted to the synthesis of the heaviest elements through nearly symmetric heavy ions fusion. The latter is known to present fusion hindrance. This phenomenon is illustrated through the TDEDF formalism. A test experiment has finally been undertaken at GANIL for the system Xe{136}+Sn{124}->Rf{260}*. No evaporation residue has been identified, and a maximal cross-section of 81 pb has been deduced for the 2n channel. Experimental difficulties encountered during this experiment are discussed, in particular in the perspective of the use of a new generatio of radioactive ions beams such as those which will be available at Spiral2.Ce mémoire traite de différents aspects des phénomènes collectifs rencontrés en dynamique nucléaire. Le formalisme de la densité fonctionnelle d'énergie dépendante du temps (TDEDF) constitue un des modèles les plus aboutis pour réaliser de telles études. Une des premières implémentations du formalisme TDEDF permettant de traiter l'appariement nucléaire, basée sur la résolution des équations Hartree-Fock-Bogoliubov dépendantes du temps, est présentée. Dans une seconde partie, le formalisme TDEDF est appliqué à l'étude de certaines excitations collectives du noyau. Tout d'abord, l'accent est mis sur les propriétés de structure et de décroissance de la résonance géante monopolaire pour des noyaux à (sous-)couche fermée. Un autre mode d'excitation du noyau atomique est ensuite étudié : les vibrations d'appariement. L'impact des fonctionnelles utilisées a été discuté. La troisième partie est dédiée à l'étude de la synthèse des éléments les plus lourds par fusion d'ions lourds presque symétriques. Ces réactions sont sujettes au phénomène de suppression de la fusion. Ce dernier est illustré au moyen du formalisme TDEDF. Une expérience test sur la fusion par voie symétrique, menée au GANIL sur le système Xe{136}+Sn{124}->Rf{260}*, est ensuite analysée. Aucun résidu d'évaporation n'a été observé. Une section efficace maximale de fusion-évaporation de 81 pb a été obtenue pour la voie 2n. Les difficultés expérimentales rencontrées sont discutées et mises en perspectives avec l'avènement d'une nouvelle génération de faisceaux d'ions radioactifs tels que ceux qui seront disponibles avec Spiral2

A New Point Kernel Sampling Scheme and Monte Carlo Transport

Starting from an existing point kernel intergrated over the bounding surface of a volume source [1], the present contribution proposes a new point kernel sampling scheme. This sampling scheme is shown to be more effcient than the standard one because the integration proceeds from line segment sources instead of point sources. A new kind of Monte Carlo transport process is proposed. It is called flux transport from a line source and is expected to be more effcient than the standard source transport

Mouvements collectifs dans les noyaux (des vibrations à la fusion)

Ce mémoire traite différents aspects des phénomènes collectifs rencontrés en dynamique nucléaire. A cette fin, le formalisme de la densité fonctionnelle d énergie dépendante du temps (TDEDF) constitue un des modèles les plus aboutis. Une des premières implémentations du formalisme TDEDF permettant de traiter l appariement nucléaire, basée sur la résolution des équations Hartree-Fock-Bogoliubov dépendantes du temps a été présentée. Dans une seconde partie, le formalisme TDEDF est appliqué à l étude de certaines excitations collectives du noyau. Tout d abord, l accent a été mis sur les propriétés de structure et de décroissance de la résonance géante monopolaire pour des noyaux à (sous)-couche fermée. Ensuite, un autre mode d excitation du noyau atomique a été étudié : les vibrations d appariement. L impact des fonctionnelles utilisées a été discuté. La troisième partie a été dédiée à l étude de la synthèse éléments les plus lourds par fusion d ions lourds presque symétriques. Ces réactions sont sujettes au phénomène de suppression de la fusion. Ce dernier a été illustré au moyen du formalisme TDEDF. Une expérience test sur la fusion par voie symétrique a été menée au Ganil sur le système 136Xe + 124Sn->260Rf* Aucun résidu d évaporation n a été décelé. Une section efficace maximale de fusion-évaporation a été obtenue. Les difficultés expérimentales rencontrées sont discutées et mises en perspectives avec les faisceaux d ions radioactifs prochainement disponibles à Ganil grâce à Spiral2.This manuscript is devoted to the study of some collective behaviors encountered in nuclear physics. The time dependent energy density functional method (TDEDF) are to that purpose one of the most achieved model. One of the first implementation of TDEDF formalism treating pairing correlation (through the resolution of the time dependent Hartree-Fock-Bogoliubov equations) is presented. In a second part, we apply the TDEDF formalism to the study of some collective excitations. First, the work has been focused on the study of structure and decay properties of the giant monopole resonance in some closed shells nuclei. The study of another type of excitation of the atomic nucleus has also been investigated : the pairing vibrations. The impact of the use of different energy density functionals has been discussed . The third part of this work has been devoted to the synthesis of the heaviest elements through nearly symmetric heavy ions fusion. The latter is known to present fusion hindrance. This phenomenon has been illustrated through the TDEDF formalism. A test experiment has finally undertaken at Ganil for the system 136Xe + 124Sn->260Rf*. No evaporation residue has been identified, and a maximal cross-section has been deduced. Experimental difficulties encountered during this experiment are discussed, in particular in the perspective of the use of radioactive ions beams which will be soon available at Ganil with Spiral2.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF