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Register a new userCoulomb distortion and medium corrections in nucleon-removal reactions
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One-nucleon removal reactions at or above the Fermi energy are important tools to explore the single-particle structure of exotic nuclei. Experimental data must be compared with calculations to extract structure information, evaluate correlation effects in nuclei or determine reaction rates for nuclear astrophysics. However, there is insufficient knowledge to calculate accurately the cross sections for these reactions. We evaluate the contributions of the final state interaction (FSI) and of the medium modifications of the nucleon-nucleon interactions and obtain the shapes and magnitudes of momentum distributions. Such effects have been often neglected in the literature. Calculations for reactions at energies 35 - 1000 MeV/nucleon are reported and compared to published data. For consistency, the state-of-the-art eikonal method for stripping and diffraction dissociation is used. We find that the two effects are important and their relative contributions vary with the energy and with the atomic and mass number of the projectile involved. These two often neglected effects modify considerably the one-nucleon removal cross sections. As expected, the effect are largest at lower energies, around 50 MeV/nucleon and on heavy targets.
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An approach to the Generator Coordinate Method (GCM) using Skyrme-type effective forces and Woods-Saxon construction potential is applied to calculate the single-particle proton and neutron overlap functions in $^{40}$Ca. The relationship between the bound-state overlap functions and the one-body density matrix has been used. These overlap functions are applied to calculate the cross sections of one-nucleon removal reactions such as ($e,ep$), ($gamma,p$) and ($p,d$) on $^{40}$Ca on the same theoretical footing. A consistent description of data for the different reactions is achieved. The shapes of the experimental cross sections for transitions to the $3/2^{+}$ ground state and the first $1/2^{+}$ excited state of the residual nuclei are well reproduced by the overlap functions obtained within the GCM. An additional spectroscopic factor accounting for correlations not included in the overlap function must be applied to the calculated results to reproduce the size of the experimental cross sections.
We develop a fully relativistic DWIA model for photonuclear reactions using the relativistic mean field theory for the bound state and the Pauli reduction of the scattering state which is calculated from a relativistic optical potential. Results for the 12C(gamma,p) and 16O(gamma,p) differential cross sections and photon asymmetries are displayed in a photon energy range between 60 and 257 MeV, and compared with nonrelativistic DWIA calculations. The effects of the spinor distortion and of the effective momentum approximation for the scattering state are discussed. The sensitivity of the model to different prescriptions for the one-body current operator is investigated. The off-shell ambiguities are large in (gamma,p) calculations, and even larger in (gamma,n) knockout.
We extend our approach to incorporate the proton-proton (pp) Coulomb force into the three-nucleon (3N) momentum-space Faddeev calculations of elastic proton-deuteron (pd) scattering and breakup to the case when also a three-nucleon force (3NF) is acting. In addition we formulate that approach in the application to electron- and gamma-induced reactions on 3He. The main new ingredient is a 3-dimensional screened pp Coulomb t-matrix obtained by a numerical solution of a 3-dimensional Lippmann-Schwinger equation (LSE). The resulting equations have the same structure as the Faddeev equations which describe pd scattering without 3NF acting. That shows the practical feasibility of both presented formulations.
The eikonal reaction theory (ERT) proposed lately is a method of calculating one-neutron removal reactions at intermediate incident energies in which Coulomb breakup is treated accurately with the continuum discretized coupled-channels method. ERT is extended to two-neutron removal reactions. ERT reproduces measured one- and two-neutron removal cross sections for 6He scattering on 12C and 208Pb targets at 240 MeV/nucleon and also on a 28Si target at 52 MeV/nucleon. For the heavier target in which Coulomb breakup is important, ERT yields much better agreement with the measured cross sections than the Glauber model.
We provide a summary of new developments in the area of direct reaction theory with a particular focus on one-nucleon transfer reactions. We provide a status of the methods available for describing (d,p) reactions. We discuss the effects of nonlocality in the optical potential in transfer reactions. The results of a purely phenomenological potential and the optical potential obtained from the dispersive optical model are compared; both point toward the importance of including nonlocality in transfer reactions explicitly. Given the large ambiguities associated with optical potentials, we discuss some new developments toward the quantification of this uncertainty. We conclude with some general comments and a brief account of new advances that are in the pipeline.
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