Exploring dissipative processes at high angular momentum in58Ni+60Ni reactions

E Williams,C Simenel,C.S Palshetkar,K Ramachandran,D.Y Jeung,D.C Rafferty,D.H Luong,S.D Mcneil,K.J Cook,E.C Simpson,D.J Hinde,M Dasgupta,A Wakhle,I.P Carter,V Greco,F Rizzo,M La Cognata,S Pirrone,C Spitaleri

doi:10.1051/epjconf/201611708021

E Williams, C Simenel + Show 17 more

Open Access

https://doi.org/10.1051/epjconf/201611708021

Copy DOI

Abstract

Current coupled channels (CC) models treat fusion as a coherent quantum-mechanical process, in which coupling between the collective states of the colliding nuclei influences the probability of fusion in near-barrier reactions. While CC models have been used to successfully describe many experimental fusion barrier distribution (BD) measurements, the CC approach has failed in the notable case of 16 O+208 Pb. The reason for this is poorly understood; however, it has been postulated that dissipative processes may play a role. Traditional BD experiments can only probe the physics of fusion for collisions at the top of the Coulomb barrier (L = 0ħ). In this work, we will present results using a novel method of probing dissipative processes inside the Coulomb barrier. The method exploits the predicted sharp onset of fission at L ~ 60ħ for reactions forming compound nuclei with A Ni+60 Ni reaction at a range of energies, in order to explore dissipative processes at high angular momentum. In this reaction, deep inelastic processes have been found to set in before the onset fission at high angular momentum following fusion. The results will be discussed in relation to the need for a dynamical model of fusion.

Highlights

In the study of nuclear reactions, one of the most elusive goals of the field has been to develop a comprehensive model of nuclear reactions: one which is capable of predicting the probabilities of the full range of possible reaction outcomes, for the complete range of nuclear collisions
We present the first study to test this high angular momentum separation method, for the 58Ni+60Ni reaction
The results of this work are summarized by the mass ratio versus total kinetic energy (TKE) plots shown in Fig. 2 for three representative above-barrier runs

Summary

Introduction

In the study of nuclear reactions, one of the most elusive goals of the field has been to develop a comprehensive model of nuclear reactions: one which is capable of predicting the probabilities of the full range of possible reaction outcomes, for the complete range of nuclear collisions. We can minimise the importance of one or two variables through clever tricks, or compare data with models reliant on different assumptions in an effort to tease out the physics behind any disagreement. No single answer exists for most experiment-model disagreements. One example of this can be found in the body of work surrounding 16O+208Pb fusion cross sections. High precision cross section data below and well above the Coulomb barrier cannot be consistently reproduced with a coupled channels model of fusion, unless one is willing to use different nuclear potential parameters to reproduce the data below and above the Coulomb barrier [1]. Though, all explanations amount to adding another parameter or two into an already parameter-heavy model, in an effort to make the model fit the data

Objectives

Methods

Results

Conclusion