Geoscience Reference
In-Depth Information
Dominant nucleosynthetic process
r
p
s
Shielded
s
+
r
103Rh
96Ru
101Ru
98Ru
99Ru
100Ru
102Ru
104Ru
94Mo
95Mo
96Mo
97Mo
98Mo
92Mo
100Mo
93Nb
90Zr
91Zr
92Zr
94Zr
96Zr
89Y
Beta decay
s
pathway
r
pathway
Neutron addition
Figure 12.4
Example of nucleosynthesis by neutron capture for elements heavier than Fe. Slow
s
processes
represent an equilibrium between neutron addition and
β
−
decay. Rapid (
r
) addition of neutrons
in the expanding core of some stars produces neutron-rich isotopes by
β
−
decay. The
p
process
yields proton-rich nuclei located above the valley of stability by reaction of the nuclides
with high gamma radiation emitted by supernovae. Note the shielded isotopes between stable
nuclides.
neutron absorption on the progeny, which, for stable isotopes, leads through
(12.1)
to the
simple relationship:
σ
i
n
i
=
σ
i
−
1
n
i
−
1
(12.3)
An
s
pathway may be easily constructed, with its branchings and accumulation points,
and the natural abundances of
s
nuclides can be successfully predicted as a function of
the neutron flux. The odd nuclides have in general larger cross-sections and therefore are
