Smooth transition from sudden to adiabatic states in heavy-ion fusion reactions at deep-subbarrier incident energies

Takatoshi Ichikawa,Akira Iwamoto,Kouichi Hagino

doi:10.1051/epjconf/20111707001

Abstract

We propose a novel extension of the standard coupled-channel (CC) model in order to account for the steep falloff of fusion cross sections at deep-subbarrier incident energies. We introduce a damping factor in the coupling potential in the CC model, simulating smooth transitions from sudden to adiabatic states in deep- subbarrier fusion reactions. The CC model extended with the damping factor can reproduce well not only the steep falloff of the fusion cross section but also the saturation of the logarithmic derivatives for the fusion cross sections at deep-subbarier energies for the 16 O+ 208 Pb, 64 Ni+ 64 Ni, and 58 Ni+ 58 Ni reactions at the deep-subbarrier energies.

Highlights

Channel couplings play an important role in heavy-ion fusion reactions at below the Coulomb barrier as a typical example of quantum tunneling of many-body systems
Because of a recent progress in experimental techniques, it has been possible to measure fusion cross sections down to deep-subbarrier incident energies [1,2,3]. These data show a substantial reduction of fusion cross sections at deepsubbarrier energies from the prediction of the CoupledChannel (CC) calculations that reproduce the experimental data at energies around the Coulomb barrier
We will show below that VTouch calculated using several kinds of ion-ion potential clearly correlates with experimentally determined threshold energy Es for many systems, indicating strongly that the nuclear interaction in the overlapping region plays an important role in the deep-subbarrier hindrance

Summary

Introduction

Channel couplings play an important role in heavy-ion fusion reactions at below the Coulomb barrier as a typical example of quantum tunneling of many-body systems. Based on the sudden picture, Misicu and Esbensen have introduced a repulsive core due to the Pauli exclusion principle to the nuclear interaction in the overlap region with the frozen-density approximation [4,5,6] They obtained a much shallower potential pocket than the conventional one, resulting in the hindrance of the fusion probability due to the cutoff of high partial waves. In the estimation of Dasgupta et al, it was impossible to obtain an overall fit to the experimental data from the above-barrier to deepsubbarrier regions with a single parameter set for the nuclear potential [7]

Correlation of threshold incident energy with energy at touching point

Damping of coupling potential in coupled-channel model

Results and discussions

Summary