Beta Decay

Once, beta decay was thought to have violated energy conservation laws, since betas are emitted with a range of energies when, in a proton – rich environment, a neutron decays into a proton with the emission of a high speed electron and an antineutrino. It took a while to discover the antineutrino which soaked up the remaining energy. This is beta-minus decay.

If we really want to tell it like it is, then this is a bit better. The neutron’s udd quark flips to a proton’s udu and the intermediate exchange particle is a W- boson

Beta + decay works in reverse. A proton changes into a neutron an antielectron and a neutrino.

Energy is required and this only happens if the  binding energy of the mother nucleus is greater than that of the daughter. The difference between them fuels the conversion plus the kinetic energy of emitted particles.

Here are two examples, one of each.

More properly, we should show charge conservation rather like this..

Both types are ultrarelativistic, in other words, the particles are emitted at close to the speed of light. Beta – decays occur above the N-Z line  and beta + below it.

After either alpha or beta decay, the nucleus is left in an excited state, frequently decaying itself to a ground state by gamma emission. I like to think of the nucleus ‘shrugging its shoulders’. No change in nucleon or proton number, we can represent the decay by adding this.


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