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

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

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

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