Neutrinos and beta decay
Posted in Physics, Probing deep into matterThe neutrino is a lepton particle and has a lepton number of 1 (antineutrinos have a lepton number of -1). It is a light particle which travels at close to the speed of light. It has no charge and interacts so weakly they are near impossible to detect. It took 26 years for the extistence of the neutrino to be proven in experiments.
Role in beta decay
The neutrino was theorised by Wolfgang Pauli to account for the problem of energy conservation in beta decay.
A decay equation for Thorium-234 which beta decays into Protactinium-234 could be written as:
If energy is to be conserved, the energy of the emitted electron must be a fixed value - the difference in energies of Thorium-234 and Protactinium-234. Experiments however show this is not the case, so does beta decay violate energy conservation laws? No, when beta decay occurs an electron is emitted together with an antineutrino. This carries away some of the energy from the interaction. The full decay equation should be written as:
Energy is now conserved with the antineutrino accounting for the extra energy. We can check that charge, lepton and baryon numbers are also conserved:
- Charge: 90 = 91 - 1 + 0
- Lepton number: 0 = 0 + 1 -1
- Baryon number: 234 = 234 + 0 + 0