stable and unstable nuclei

Page 1

The strong nuclear interaction: this is the force that binds nucleons together. Gravity is far too weak to overcome electrostatic forces, so there must be a strong nuclear force to hold it together.

Distance and the strong nuclear interaction: The force has a very short range (up to a few femtometres) about the size of a nucleus.

At very small separations, the force is repulsive, otherwise the force would crush the nucleus to a point.

It works equally between all nucleons, for instance a proton-proton interaction will have the same force as a neutron-proton interaction.

(The electrostatic force has an indefinite range)

alpha emission:

238 234 4

U ==> Th + α

92 90 2

only happens in very large atoms, as nucleons are too far apart for the strong nuclear force to keep them stable (see page 1)

^

nucleon number decreases by 4, proton number decreases by 2.

an alpha particle has 2 protons and 2 neutrons, same as a helium nucleus.

beta emission:

187 187 _

Re ==> Os + β + ve

75 76

happens in isotopes that have a lot more neutrons than protons.

one of the neutrons in the nucleus changes into a proton and ejects a beta minus particle, which conserves charge.

the anti electron-neutrino has no charge, but carries away some energy and momentum.

the product atom has the same number of nucleons, but one more proton.

forces and stable nuclei

unstable nuclei, alpha and beta emission