Nucleosynthesis

1
Nucleosynthesis
WoodstockWell I came across a child of God, he
was walking along the roadand I asked him tell
where are you going, this he told meWell, Im
going down to Yasgur's farm, going to join in a
rock and roll band.Got to get back to the land,
set my soul free.We are stardust, we are golden,
we are billion year old carbon,and we got to get
ourselves back to the garden. - Crosby, Still,
Nash and Young
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Nucleosynthesis
We have already described many of the reactions
that produce elements up through iron. Beyond
iron, heavier elements are synthesized through
neutron capture.
3
Nucleosynthesis
We have already described many of the reactions
that produce elements up through iron. Beyond
iron, heavier elements are synthesized through
neutron capture.
AZ X n ? A1Z Y
4
Nucleosynthesis
We have already described many of the reactions
that produce elements up through iron. Beyond
iron, heavier elements are synthesized through
neutron capture.
AZ X n ? A1Z Y
Neutron capture is fairly slow
process. s-process The relatively slow process
of neutron capture.
5
Nucleosynthesis
We have already described many of the reactions
that produce elements up through iron. Beyond
iron, heavier elements are synthesized through
neutron capture.
AZ X n ? A1Z Y
After (possible multiple) neutron capture, the
isotope can become unstable.
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Nucleosynthesis
The isotope can then undergo beta decay, forming
an element higher on the periodic table.
? emission The beta particle is an electron (
0-1 ?) AZ X ? AZ1 Y 0-1? photon
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Nucleosynthesis
Neutron capture and radioactive decay can account
for the formation of most of the heavier
elements. The heaviest elements are believed to
be created by a different process than the
s-process. The neutron rich environment can
result in rapid multiple neutron
capture. r-process the rapid capture of
neutrons by nuclei during a supernova event.
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Nucleosynthesis
What is the evidence? Light curves of a
supernova event. Recall The light curves will
mimic the radioactive decay of unstable
elements. Observed light curves do, in fact,
mimic the radioactive decay of known
elements. See Figure 21.18
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Nucleosynthesis
This figure shows the relative abundances
resulting from a calculation of the explosive
burning of silicon (shown as crosses and dashed
lines) compared to the actual abundances (shown
as solid squares and lines) observed throughout
the cosmos. The crosses are very close to the
squares for the more abundant elements (such as
Si, S, Ar, Ca, Cr, Fe), giving us confidence that
these elements can be produced in the observed
ratios by such reactions.