Surface-peaked medium sensitivity of the optical potential: an exact result

Microscopic optical model potentials for elastic hadron-nucleus scattering usually take the form of a convolution of a two-body effective interaction with the target ground-state mixed density. Within the Brueckner-Bethe-Goldstone gmatrix approach for the effective interaction, nuclear medium effects are made explicit by means spatial integrals throughout the bulk of the nucleus. In this contribution we discuss a novel and exact approach to track down the manifestation of intrinsic nuclear medium effects. After examining the momentumand coordinate-space structure of a two-body effective interaction –spherically symmetric in its mean coordinate– it is demonstrated that the intrinsic medium effects in the optical potential depend solely on the gradient of a reduced interaction. This feature implies the confinement of intrinsic medium effects to regions where the density varies most, i.e. the nuclear surface. This finding may be of special significance in the study of nuclear collisions sensitive to the peripheric structure of nuclei. We illustrate some of its implications in the context of 10Be + p elastic scattering at 39.1A MeV

Functional medium-dependence of the nonrelativistic optical model potential

By examining the structure in momentum and coordinate space of a two-body interaction spherically symmetric in its local coordinate, we demonstrate that it can be disentangled into two distinctive contributions. One of them is a medium-independent and momentum-conserving term, whereas the other is functionally --and exclusively-- proportional to the radial derivative of the reduced matrix element. As example, this exact result was applied to the unabridged optical potential in momentum space, leading to an explicit separation between the medium-free and medium-dependent contributions. The latter does not depend on the strength of the reduced effective interaction but only on its variations with respect to the density. The modulation of radial derivatives of the density enhances the effect in the surface and suppresses it in the saturated volume. The generality of this result may prove to be useful for the study of surface-sensitive phenomena.Comment: 11 pages, 5 figures, submitted to Phys. Rev.

Probing Correlated Ground States with Microscopic Optical Model for Nucleon Scattering off Doubly-Closed-Shell Nuclei

The RPA long range correlations are known to play a significant role in understanding the depletion of single particle-hole states observed in (e, e') and (e, e'p) measurements. Here the Random Phase Approximation (RPA) theory, implemented using the D1S force is considered for the specific purpose of building correlated ground states and related one-body density matrix elements. These may be implemented and tested in a fully microscopic optical model for NA scattering off doubly-closed-shell nuclei. A method is presented to correct for the correlations overcounting inherent to the RPA formalism. One-body density matrix elements in the uncorrelated (i.e. Hartree-Fock) and correlated (i.e. RPA) ground states are then challenged in proton scattering studies based on the Melbourne microscopic optical model to highlight the role played by the RPA correlations. Effects of such correlations which deplete the nuclear matter at small radial distance (r $<$ 2 fm) and enhance its surface region, are getting more and more sizeable as the incident energy increases. Illustrations are given for proton scattering observables measured up to 201 MeV for the $^{16}$O, $^{40}$Ca, $^{48}$Ca and $^{208}$Pb target nuclei. Handling the RPA correlations systematically improves the agreement between scattering predictions and data for energies higher than 150 MeV.Comment: 20 pages, 7 figure

Challenging Nuclear Structure Models Through a Microscopic Description of Proton Inelastic Scattering off 208Pb

A fully microscopic calculation of inelastic proton scattering off {sup 208}Pb is presented, and compared to experimental scattering data for incident proton energies between 65 and 201 MeV. By constructing the nucleon-nucleus interaction through the folding of nuclear structure information with a reliable nucleon-nucleon effective interaction that has no adjusted parameter, a consistent framework is built, for probing the influence of different descriptions of nuclear structure on nucleon inelastic scattering predictions. The absence of phenomenological normalization in this framework guarantees a unique and unambiguous interpretation of our calculations in terms of quality of the underlying nuclear structure description: a feature that had been reserved, until recently, to the electron probe. This tool is used to investigate the effect of long range correlations embedded in excited states, on calculated inelastic observables, demonstrating the sensitivity of nucleon scattering predictions to details of the nuclear structure

Quantum corrections for pion correlations involving resonance decays

A method is presented to include quantum corrections into the calculation of two-pion correlations for the case where particles originate from resonance decays. The technique uses classical information regarding the space-time points at which resonances are created. By evaluating a simple thermal model, the method is compared to semiclassical techniques that assume exponential decaying resonances moving along classical trajectories. Significant improvements are noted when the resonance widths are broad as compared to the temperature.Comment: 9 pages, 4 figure

Predicting total reaction cross sections for nucleon-nucleus scattering

Nucleon total reaction and neutron total cross sections to 300 MeV for 12C and 208Pb, and for 65 MeV spanning the mass range, are predicted using coordinate space optical potentials formed by full folding of effective nucleon-nucleon interactions with realistic nuclear ground state densities. Good to excellent agreement is found with existing data.Comment: 10 pages, 4 figure

Asymptotic normalization coefficient of ^{8}B from breakup reactions and the S_{17} astrophysical factor

We show that asymptotic normalization coefficients (ANC) can be extracted from one nucleon breakup reactions of loosely bound nuclei at 30-300 MeV/u. In particular, the breakup of ^{8}B is described in terms of an extended Glauber model. The 8B ANC extracted for the ground state of this nucleus from breakup data at several energies and on different targets, C^2 = 0.450+/-0.039} fm^-1, leads to the astrophysical factor S_{17}(0)= 17.4+/-1.5 eVb for the key reaction for solar neutrino production 7Be(p,gamma)8B. The procedure described here is more general, providing an indirect method to determine reaction rates of astrophysical interest with beams of loosely bound radioactive nuclei.Comment: 4 pages, RevTex, 3 figures revised version to appear in Phys Rev Let

Nuclear Data for Sustainable Nuclear Energy

Final report of a coordinated action on nuclear data for industrial development in Europe (CANDIDE). The successful development of advanced nuclear systems for sustainable energy production depends on high-level modelling capabilities for the reliable and cost-effective design and safety assessment of such systems, and for the interpretation of key benchmark experiments needed for performance and safety evaluations. High-quality nuclear data, in particular complete and accurate information about the nuclear reactions taking place in advanced reactors and the fuel cycle, are an essential component of such modelling capabilities. In the CANDIDE project, nuclear data needs for sustainable nuclear energy production and waste management have been analyzed and categorized, on the basis of preliminary design studies of innovative systems. Meeting those needs will require that the quality of nuclear data files be considerably improved. The CANDIDE project has produced a set of recommendations, or roadmap, for sustainable nuclear data development. In conclusion, a substantial long-term investment in an integrated European nuclear data development program is called for, complemented by some dedicated actions targeting specific issues.JRC.D.5-Neutron physic

Signals for a Transition from Surface to Bulk Emission in Thermal Multifragmentation

Excitation-energy-gated two-fragment correlation functions have been studied between 2 to 9A MeV of excitation energy for equilibrium-like sources formed in $\pi^-$ and p + $^{197}$Au reactions at beam momenta of 8,9.2 and 10.2 GeV/c. Comparison of the data to an N-body Coulomb-trajectory code shows a decrease of one order of magnitude in the fragment emission time in the excitation energy interval 2-5A MeV, followed by a nearly constant breakup time at higher excitation energy. The observed decrease in emission time is shown to be strongly correlated with the increase of the fragment emission probability, and the onset of thermally-induced radial expansion. This result is interpreted as evidence consistent with a transition from surface-dominated to bulk emission expected for spinodal decomposition.Comment: 11 pages including 3 postscript figures (1 color