Isospin Conservation in Neutron Rich Systems of Heavy Nuclei

Ashok Kumar Jain,Swati Garg

doi:10.1051/epjconf/201817805007

Abstract

It is generally believed that isospin would diminish in its importance as we go towards heavy mass region due to isospin mixing caused by the growing Coulomb forces. However, it was realized quite early that isospin could become an important and useful quantum number for all nuclei including heavy nuclei due to neutron richness of the systems [1]. Lane and Soper [2] also showed in a theoretical calculation that isospin indeed remains quite good in heavy mass neutron rich systems. In this paper, we present isospin based calculations [3, 4] for the fission fragment distributions obtained from heavy-ion fusion fission reactions. We discuss in detail the procedure adopted to assign the isospin values and the role of neutron multiplicity data in obtaining the total fission fragment distributions. We show that the observed fragment distributions can be reproduced rather reasonably well by the calculations based on the idea of conservation of isospin. This is a direct experimental evidence of the validity of isospin in heavy nuclei, which arises largely due to the neutron-rich nature of heavy nuclei and their fragments. This result may eventually become useful for the theories of nuclear fission and also in other practical applications.

Highlights

Isospin is a useful and fundamental quantum number in nuclear and particle physics
The third component of isospin is different for both the states, T3 = +1/2 for neutron and T3 = −1/2 for proton. This convention is just opposite to what is normally used in particle physics
Theoretical predictions for the drip lines are shown by the wavy lines, while the presently known experimental limits are shown by joining the known data points

Summary

Introduction

Isospin is a useful and fundamental quantum number in nuclear and particle physics. In nuclei, we consider neutron and proton to be the two isospin states of a common entity called a nucleon with isospin T = 1/2. The experimental data on fission fragment distributions of heavy nuclei is a good testing ground for verifying the conservation of isospin in heavy nuclei. More precise fragment distribution data of HI induced fission are becoming available where gamma ray spectroscopy of fragments are being used to identify each fragment, only in even-even nuclei so far. Sliv and Kharitonov (1965) [5] calculated the isospin admixture in light (N = Z) nuclei and heavy (N > Z) nuclei by using harmonic oscillator shell model wave functions and showed that the isospin admixture in the ground state of 16O is nearly same as in 208Pb. A detailed discussion of some these developments may be found in the review by Auerbach [6]. There are a some deviations which may be due to the presence of shell closure or the presence of isomers

Formalism

Results and Discussion

Conclusion