934 research outputs found

    Coupling of giant resonances to soft E1 and E2 modes in B-8

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    The dynamic coupling between giant resonance states and "soft", low-energy excitation, modes in weakly-bound nuclei is investigated. A coupled-channels calculation is reported for the reaction 8B + Pb --> p + 7Be + Pb at 83 MeV/nucleon. It is shown that the low-energy response is only marginally modified by transitions to the isovector giant dipole and isoscalar giant quadrupole resonances.Comment: 8 pages, 2 figure

    A Computer Program for Relativistic Multiple Coulomb and Nuclear Excitation

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    A computer program is presented by which one may calculate the multiple electric dipole, electric quadrupole and magnetic dipole Coulomb excitation with relativistic heavy ions. The program applies to an arbitrary nucleus, specified by the spins and energies of the levels and by all E1, E2 and M1 matrix elements. Nuclear excitation is calculated optionally for monopole, dipole and quadrupole excitations and needs inputs of optical potentials. For given bombarding conditions, the differential cross sections and statistical tensors (useful to calculate gamma-ray angular distribution functions) are computed.Comment: 10 page

    Pauli blocking and medium effects in nucleon knockout reactions

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    We study medium modifications of the nucleon-nucleon (NN) cross sections and their influence on the nucleon knockout reactions. Using the eikonal approximation, we compare the results obtained with free NN cross sections with those obtained with a purely geometrical treatment of Pauli-blocking and with NN obtained with more elaborated Dirac-Bruecker methods. The medium effects are parametrized in terms of the baryon density. We focus on symmetric nuclear matter, although the geometrical Pauli-blocking allows for the treatment of asymmetric nuclear matter. It is shown that medium effects can change the nucleon knockout cross sections and momentum distributions up to 10% in the energy range E=50-300 MeV/nucleon. The effect is more evident in reactions involving halo nuclei.Comment: 10 pages, 9 figures, accepted for publication in Physics Review

    Breakup of the weakly bound 17F nucleus

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    The breakup of the radioactive 17F nucleus into a proton and 16O is studied for the reaction 17F + 208Pb --> p + 16O + 208Pb at 65 MeV/nucleon. The possibility of using this reaction as a test case for studying dynamical Coulomb reacceleration effects is assessed. It is shown that the reaction is dominated by elastic nuclear breakup (diffraction dissociation).Comment: 17 figures and 8 figure

    Short-range correlations in two-nucleon knockout reactions

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    A theory of short-range correlations in two-nucleon removal due to elastic breakup (diffraction dissociation) on a light target is developed. Fingerprints of these correlations will appear in momentum distributions of back-to-back emission of the nucleon pair. Expressions for the momentum distributions are derived and calculations for reactions involving stable and unstable nuclear species are performed. The signature of short-range correlations in other reaction processes is also studied.Comment: Nuclear Physics A, in pres

    Quenching of 1+1^+ excitations in the double giant resonance

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    The electromagnetic excitation of the two-phonon isovector giant dipole resonance in relativistic projectiles incident on heavy targets can be proceed via several intermediate 1‚ąí1^- one-phonon giant resonance states. In two step electric dipole transitions the population of 0+0^+, 1+1^+, and 2+2^+ two-phonon states are possible. We calculate the amplitude distribution of 1‚ąí1^- excitations with an RPA formalism, and use it to calculate the electromagnetic excitation of two-phonon states in second order perturbation theory and coupled-channels. We show that a conspiracy between angular momentum coupling and the strength of the electromagnetic fields suppresses contributions of 1+1^+ states to the total cross sections.Comment: 10 pages, 2 Postscript figures available upon reques

    And there was light

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    I discuss the use of light as a collection of real and virtual photons to study lingering questions in particle and nuclear physics.Comment: 9 pages, 5 figures, 4 tables, Invited Lecture at the Carpathian Summer School of Physics 2014, Exotic Nuclei and Nuclear/Particle Astrophysics (V), July 13-26, Sinaia, Romani

    Pygmy resonances and symmetry energy

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    I present a brief summary of the first three decades of studies of pygmy resonances in nuclei and their relation to the symmetry energy of nuclear matter. I discuss the first experiments and theories dedicated to study the electromagnetic response in halo nuclei and how a low energy peak was initially identified as a candidate for the pygmy resonance. This is followed by the description of a collective state in medium heavy and heavy nuclei which was definitely identified as a pygmy resonance. The role of the slope parameter of the symmetry energy in determining the properties of neutron stars is stressed. The theoretical and experimental information collected on pygmy resonances, neutron skins, and the numerous correlations found with the slope parameter is briefly reviewed.Comment: 9 pages, Contribution to the special issue of EPJA on the topic "Giant, Pygmy, Pairing Resonances and related topics" dedicated to the memory of Pier Francesco Bortignon. Additional references include

    Nuclear astrophysics studies with ultra-peripheral heavy-ion collisions

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    I describe in very simple terms the theoretical tools needed to investigate ultra-peripheral nuclear reactions for nuclear astrophysics purposes. For a more detailed account, see arXiv:0908.4307.Comment: 12 pages, 8 figures, Lecture notes presented at the 5th European Summer School on Experimental Nuclear Astrophysics, Sep. 20- 27, 2009, Santa Tecla, Sicily, Italy. AIP proceedings, to be publishe
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