Neutrinos and Heavy-Element
Nucleosynthesis
Brad Meyer
Clemson University
Neutrinos do two things:
• Change nucleons:
– Nu + n  p + e– Antinu + p  n + e+
• Spall nucleons
– Nu + (Z,A)  (Z,A-1) + n
– Nu + (Z,A)  (Z-1,A-1) + p
Alpha-Effect I
• Fuller and Meyer 1995
• Neutrino captures during buildup of 4He
• Can drastically increase Ye =>reduce
efficacy of the r-process
Meyer, McLaughlin, and Fuller 1998
Alpha Effect II
•
•
•
•
Meyer 1995
Spall p’s from 4He late in expansion
These protons form 3H
3H + 4He  7Li  Heavy nuclei—reduce
neutron to seed ratio
Meyer 1995
Spallation in the r-Process
• Once the r-process has finished, neutrinos
spall off neutrons
• Tends to smooth out the abundances but
also fills in gaps that should be present in
the abundance distribution
Meyer et al. 1992
Neutrino Capture on All Species
Species
Overproduction
94Mo
2.9 x 106
92Mo
2.1 x 106
74Se
1.9 x 106
84Sr
1.8 x 106
97Mo
1.7 x 106
Capture on Z < 40
Species
Overproduction
74Se
1.8 x 106
84Sr
1.7 x 106
90Zr
1.4 x 106
91Zr
9.6 x 105
97Mo
7.8 x 105
Conclusions
• Neutrinos can play a significant role in
heavy-element nucleosynthesis in changing
nucleons and redistributing them
• We understand most of the likely effects of
neutrinos during nucleosynthesis
• We now need to understanding the setting
of these effects—I.e. Understand
supernovae.