A seed nucleus
is an isotope
that is the starting point for any of a variety of fusion chain reactions
. The mix of nuclei produced at the conclusion of the chain reaction generally depends strongly on the relative availability of the seed nucleus or nuclei and the component being fused--whether neutrons
as in the r-process
or protons as in the rp-process
. A smaller proportion of seed nuclei will generally result in products of larger mass
, whereas a larger seed-to-neutron or seed-to-proton ratio will tend to produce comparatively lighter masses.