  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 $^{232}Th$ in the valley of stability
and exotic neutron rich isotopes $^{250}U$, $^{256}U$, $^{260}U$, $^{240}Th$,
$^{250}Th$, $^{256}Th$ likely to play important role in the r-process
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.
