Kichinosuke Harada

Microscopic calculation of friction in heavy ion reaction using linear response theory

We present a realistic calculation of the frictional coefficients for28Si+20Ne system using the two-center shell model on the basis of the linear response theory. Adopting the center separationR and the deformationδ as collective variables we study the dependence of frictional coefficients γRR, γRδ and γδδ on those variables, for various values of the neck parameterɛ, the temperatureT and the smearing widthΓ. The direct application of the linear response theory to the two-center potential gives non-vanishing friction for the simple translational motion of the two fragments even when they are far apart. A method to avoid this energy dissipation is proposed and is used in the calculation. Results show that the form factor of the frictional force is surface-peaked and the peak becomes lower as the prolate deformation or neck formation increases. Temperature dependence is mild, but is not negligible. We compare our γRR and γδδ with other models.

Alpha-Cluster and Nuclear Surface

It is shown that the internal probability density of alpha particles emitted from heavy nuclei has a maximum at the nuclear surface. The radial dependence of the overlap integral of the wave functions for four nucleons at the top levels of heavy nuclei and alpha particles was calculated using the harmonic oscillator shell model.

A numerical analysis of the heavy-ion reaction based on the linear response theory

Taking the relative distanceR and the deformationδ of each nucleus as the collective variables, we solve the two dimensional coupled dynamical equations of motion with friction in the framework of the linear response theory. In solving the equations of motion, we approximately replace the inertia tensor with the hydrodynamical one and use the modified liquid-drop one as the collective potential energy. As the frictional coefficients we use the microscopically calculated ones in the previous paper.The calculation is done for the reaction of28Si+20Ne, in which the incident energy of20Ne is 120 MeV. Results show that our microscopically calculated friction gives the large value of energy dissipation which amounts to the “completely damped” collision. Besides it, growths of the oblate deformation in the entrance channel and the prolate deformation in the exit channel are clearly seen. They give a large influence on the time development of the energy dissipation. We compare our calculated results with the experimental data for the reactions of 120 MeV20Ne with27Al. The agreement between them is found to be reasonably good.

Pre-equilibrium description of fast light particle emission in heavy-ion reactions

Abstract Fast light particle emissions in heavy-ion reactions are described as a pre-equilibrium process. Reactions between a “light” heavy-ion projectile and a heavy target are considered in the energy region of the incident energy / the projectile mass ⪅ 10 MeV. Calculations are carried out by an extended exciton model in which the finiteness of the time needed for the fusion process is included. The spectrum shapes of proton, alpha, deuteron and triton emissions are well explained for an example case, 14 N + 181 Ta at 115 MeV .

Microscopic calculation of friction coefficients for use in heavy-ion reaction

A microscopic calculation has been done for the friction coefficient for use in the deep-inelastic collision of heavy nuclei. We adopted the formalism of the linear response theory as a basis and used the adiabatic base of the two-center shell model. Several reaction channels with the total mass numbers of 236 and 260 systems were investigated. The friction coefficients for the radial and deforming motions including the coupling term were calculated as a function of the distance between two nuclei and deformation of the two nuclei for each channel. The general feature of the friction coefficient, its strength and form factor, was clarified in this model and comparison with the results of other models were done. It was found that our model gives a physically plausible value for the friction coefficient as a whole.

On the focussing effect and the large energy loss in the quasi-fission reaction

Abstract A classical dynamical model is applied to the deep inelastic reactions between heavy ions. Assuming that the range of the nuclear interaction depends on the intrinsic excitation energies, the sharp angular distribution and the large energy loss in the quasi-fission reaction are explained systematically.

Microscopic calculation of the mass diffusion coefficient using linear response theory

Abstract The mass diffusion coefficients in deep inelastic collisions are calculated in the framework of the linear response theory, adopting a two-center harmonic oscillator hamiltonian. The experimental results are well reproduced by the calculation under the assumption that the mass transfer occurs while two nuclei form a rotating composite system at close contact, R = 1.18 (A 1 1 3 + A 2 1 3 ) fm.