•Why
can’t we keep adding neutrons rather than protons?
–They
feel strong force attraction – with no Coulomb repulsion
–You
should be able to get lots of energy by adding neutrons
–
•Nuclear
Weak Force can (slowly) convert protons to neutrons
and back
–The
reactions involve an electron or “positron” to keep charges
balanced
–The
reactions produce a new almost massless particle called a neutrino
–
–p+ + e- Û n + n p+ is proton
e- is electron
n is neutron
n is neutrino
–
–p+ Û n + e+ + n e+ is positron = antiparticle of
electron
If this second reaction happens
then the positron annihilates
the next electron it encounters,
thereby producing the
equivalent of the first
reaction.
•The
weak force likes to keep ~equal protons and neutrons in a nucleus
•The
proton repulsion tips the balance towards slightly more neutrons in big nuclei