12
The
Proton-Proton chain
•The first step is slow because it relies
on two rare events happening simultaneously
–Two protons collide with enough energy to
overcome the Coulomb barrier
–While they are close the weak force turns
one proton into a neutron
•The resulting combination of a proton and
a neutron IS a stable nucleus
–1H +
1H ®
2H +
e+ +
n p+
+ p+ ®
(p+ n)
+ e+ +
n
•The next two steps go quickly because they
rely only on the strong force
–2H +
1H ®
3H (p+ n) + p+
® (p+ p+ n
)
–3H +
3H ®
4He +
1H +
1H
(p+ p+ n) + (p+ p+ n) ® (p+ p+ n n) + p+ + p+
•The net effect is 4 1H ® 4He
From Realm of the Universe, by Abell et al.