Pre-equilibrium neutron emission in the nucleon exchange transport model

Abstract

LBL-23359We extend the Nucleon Exchange Transport model to include the emission of pre-equilibrium neutrons as a result of nucleon transfer to unbound states. The treatment takes account of the heating of the two nuclei caused by the energy dissipation and the cooling due to the pre-equilibrium emission. Furthermore, the transferred nucleons may induce cascading in the receptor nucleus by means of direct two-body scattering with the resident nucleons, based on a reduced, Pauli-blocked, energy-dependent free N N cross section. Qualitative agreement with experimental data is achieved, but the absolute multiplicities are systematically underestimated by about a factor of two. The dependence of multiplicity on bombarding energy is reproduced. The energy spectra and their variation with angle are generally reproduced, although the yield of the highest energy particles is sometimes underestimated.

Light-particle emission versus evaporation residue formation in collisions of40Ar onnatCa at 30 MeV/u

“…This kind of parametrization agrees in very good approximation with the results of a quantal phase-space model [11]. The quantity [19] (dashed curve). Since the models yield preequilibrium multiplicities, an (isotropic) equilibrium multiplicity dMe, q/d~, = 6.2/4 x = 0.5 is added to the model predictions for comparison with the measured data.…”

Cluster Emission in Complex Nuclear Reactions

“…A quantitative study of these effects can be carried out in a microcanonical approach, employing the simple model of the nucleus as a Fermi gas of nucleons interacting via realistic nuclear forces. Such interactions can be written in harmonic approximation as [56,57], (9) In this expression for the compressional nuclear energy, the quantity En ~ 8 MeV is the average nucleon binding energy. The total excitation energy of a nucleus is then the sum of (collective) compression and (random) thermal excitation energies,…”

“…These relations are dynamically dependent on bombarding energy, impact parameter, and the energy loss in a collision. In an approximate fashion, dynamical processes, such as the emission of fast, nonequilibriurn nucleons and clusters initiated by the exchange of nucleons between projectile and target, can be modeled [9,18] by integrating corresponding kinetic rate equations along the trajectories defined by Eq. (2).…”

“…Consequently, macroscopic properties of the interaction partners, such as Ai, Zi, Ei (thermal excitation), and Ji (spin), vary in a stochastic fashion for each nucleus i. With certain probabilities, transferred nucleons have enough energy in the recipient nucleus to exceed its binding energy and may be emitted directly, or after a few in-medium collisions, as "Fermi jets" [8,9] or prompt particles [10]. Similar prompt-particle emission is predicted by all major theoretical approaches.…”

Inverse-kinematics study of78Kr +40Ca at 10 AMeV

“…Processes such as pre-equilibrium emission of nucleons [1][2][3], "neck" emission of intermediate-mass fragments [4,5] and dynamic fragmentation of projectile-like fragments [6,7] have developed recent interest. One method of simulating the dynamics of a many-body nuclear system is offered by the time-dependent Hartree-Fock theory (TDHF).…”