981 research outputs found

    Evolving theoretical descriptions of heavy-ion fusion :from phenomenological to microscopic approaches

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    We overview the current status of theoretical approaches for heavy-ion fusion reactions at subbarrier energies. We particularly discuss theoretical challenges in the coupled-channels approach, that include i) a description of deep subbarrier hindrance of fusion cross sections, ii) the role of nuclear dissipation, iii) fusion of unstable nuclei, and iv) an interplay between fusion and multi-nucleon transfer processes. We also present results of a semi-microscopic approach to heavy-ion fusion reactions, that combines the coupled-channels approach with state-of-the-art microscopic nuclear structure calculations.Comment: 6 pages, 5 eps figures. A talk given at the International conference on heavy-ion collisions at near-barrier energies (FUSION17), February 20-24, 2017, Hobart, Australi

    Dynamical particle-phonon couplings in proton emission from spherical nuclei

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    We present results of coupled-channels calculations which are performed to understand the role of vibrational excitations of the daughter nucleus in proton emission decay of spherical nuclei. It is shown that the experimental decay rates from the 2d3/2d_{3/2}, 3s1/2s_{1/2} and 1h11/2h_{11/2} states in proton emitting nuclei 160,161^{160,161}Re are reproduced simultaneously when the quadrupole phonon excitation of the core nuclei is taken into account. We apply the formalism also to the 145^{145}Tm nucleus and show that good agreement is achieved with the recently measured branching ratio for the fine structure.Comment: 10 pages, 3 eps figures, uses psfig.sty and ptptex.sty. A talk given at the Yukawa International Seminar 2001 on "Physics of Unstable Nuclei", Nov. 2001, Kyoto, Japa

    Importance of Non-Linear Couplings in Fusion Barrier Distributions and Mean Angular Momenta

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    The effects of higher order coupling of surface vibrations to the relative motion on heavy-ion fusion reactions at near-barrier energies are investigated. The coupled channels equations are solved to all orders, and also in the linear and the quadratic coupling approximations. It is shown that the shape of fusion barrier distributions and the energy dependence of the average angular momentum of the compound nucleus can significantly change when the higher order couplings are included. The role of octupole vibrational excitation of ^{16}O in the ^{16}O + ^{144}Sm fusion reaction is also discussed using the all order coupled-channels equations.Comment: 8 pages, 6 figures, To be published in the Proceedings of the FUSION 97 Conference, South Durras, Australia, March 1997 (J. Phys. G

    Potential inversion with subbarrier fusion data revisited

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    We invert experimental data for heavy-ion fusion reactions at energies well below the Coulomb barrier in order to directly determine the internucleus potential between the colliding nuclei. In contrast to the previous applications of the inversion formula, we explicitly take into account the effect of channel couplings on fusion reactions, by assuming that fusion cross sections at deep subbarrier energies are governed by the lowest barrier in the barrier distribution. We apply this procedure to the 16^{16}O +144^{144}Sm and 16^{16}O +208^{208}Pb reactions, and find that the inverted internucleus potential are much thicker than phenomenological potentials. A relation to the steep fall-off phenomenon of fusion cross sections recently found at deep subbarrier energies is also discussed.Comment: 5 pages, 3 eps figure

    Applicability of the orientation average formula in heavy-ion fusion reactions of deformed nuclei

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    In heavy-ion fusion reactions involving a well deformed nucleus, one often assumes that the orientation of the target nucleus does not change during the reaction. We discuss the accuracy of this procedure by analyzing the excitation function of the fusion cross section and the fusion barrier distribution in the reactions of 154^{154}Sm target with various projectiles ranging from 12^{12}C to 40^{40}Ar. It is shown that the approximation gradually looses its accuracy with increasing charge product of the projectile and target nuclei because of the effects of finite excitation energy of the target nucleus. The relevance of such inaccuracy in analyzing the experimental data is also discussed.Comment: 5 pages and 3 figure

    Continuum QRPA in the coordinate space representation

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    We formulate a quasi-particle random phase approximation (QRPA) in the coordinate space representation. This model is a natural extension of the RPA model of Shlomo and Bertsch to open-shell nuclei in order to take into account pairing correlations together with the coupling to the continuum. We apply it to the 120^{120}Sn nucleus and show that low-lying excitation modes are significantly influenced by the pairing effects although the effects are marginal in the giant resonance region. The dependence of the pairing effect on the parity of low-lying collective mode is also discussed.Comment: RevTex, 21 pages, 10 eps figure

    Odd-even staggering of reaction cross sections for 22,23,24O isotopes

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    The interaction cross sections of 22,23^{22,23}O nuclei at 900 MeV/nucleon have been measured recently by Kanungo {\it et al.}. We show that the odd-even staggering parameter of interaction cross sections deduced from these new data agrees well with the theoretical systematics expected for the neutron separation energy of SnS_n=2.74±\pm0.120 MeV for 23^{23}O. We also discuss briefly the energy dependence of the staggering parameter.Comment: 2 pages, 1 figur

    Reaction dynamics for fusion of weakly-bound nuclei

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    We discuss several open problems of fusion reactions induced by weakly bound nuclei. For this purpose, we solve a one dimensional three-body Hamiltonian with the coupled-channels formalism. We show that the continuum-continuum couplings substantially reduce the total fusion probability at energies above the barrier compared with the no-breakup case, although the fusion probability remains enhanced at subbarrier energies. We then discuss a role of transfer process in fusion of weakly bound nuclei, and point out that removing spurious Pauli forbidden transfer components from the calculation may be crucial at energies below the barrier. Calculations based on the three-body classical trajectory Monte Carlo (CTMC) method are also presented in order to discuss how to model complete fusion process.Comment: 8 pages, 3 eps figures. Uses ptptex.sty. A talk given at the International conference FUSION03, November 12 - 15, 2003, Matsushima, Miyagi, Japan. To be published in Prog. Theo. Phys. Supp
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