language: en

[Confidential: not for distribution. Submitted to IOP Publishing for peer review]

16 April 2010

Anatomy of neck configuration in fission decay

S.K. Patra 1 , R. K. Choudhury 2 and L. Satpathy 1
1 Institute of Physics,
Sachivalaya Marg, Bhubaneswar 751005, India
4 Bhaba Atomic Research Centre,
Mumbai

Abstract. The anatomy of neck configuration in the fission decay of Uranium and Thorium isotopes is investigated in a microscopic study using Relativistic mean field theory. The study includes 236 U and 232 T h in the valley of stability and exotic neutron rich isotopes 250 U , 256 U , 260 U , 240 T h, 250 T h, 256 T h likely to play important role in the rprocess nucleosynthesis in stellar evolution. Following the static fission path, the neck configurations are generated and their composition in terms of the number of neutrons and protons are obtained showing the progressive rise in the neutron component with the increase of mass number. Strong correlation between the neutron multiplicity in the fission decay and the number of neutrons in the neck is seen. The maximum neutron-proton ratio is about 5 for 260 U and 256 Th suggestive of the break down of liquid-drop picture and inhibition of the fission decay in still heavier isotopes. Neck as precursor of a new mode of fission decay like multi-fragmentation fission may also be inferred from this study.

PACS: 24.75.+i, 25.85.-w,21.10.Dr, 21.60.Jz Keywords: Nuclear Fission, neck structure, scission point, relativistic mean field formalism 1. Introduction