575 research outputs found
Pauli blocking and medium effects in nucleon knockout reactions
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
And there was light
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
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
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
One and Two-photon Physics with Relativistic Heavy Ions
The physics of peripheral collisions with relativistic heavy ions (PCRHI) is
reviewed. One- and two-photon processes are discussed.Comment: 14 pages, Invited talk at the 17th Winter Workshop on Nuclear
Dynamics, Park City, Utah, March 10-17, 200
The stopping of low energy ions in reactions of astrophysical interest
he velocity dependence of the stopping power of swift protons and deuterons
in low energy collisions with hydrogen and helium gas targets is investigated
with the numerical solution of the time-dependent Schroedinger coupled-channels
equations using molecular orbital wavefunctions. At low projectile energies the
stopping is mainly due to nuclear stopping, charge exchange of the electron,
and excitation of the lowest levels in the target. The second and third
mechanisms dominate at E < 200 eV. At lower energies it is also shown that a
threshold effect is responsible for a quick drop of the energy loss. This
investigation sheds more light on the long standing electron screening problem
in fusion reactions of astrophysical interest.Comment: 8 pages, 3 figures, presented at FUSION03, Matsushima, Miyagi, Japan,
Nov 12-15, 2003, to appear in Progress of Theoretical Physic
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