Evidence for the Neutrino (HL) (HL IB Physics)

• An electron neutrino is a type of subatomic particle with no charge and negligible mass which is also emitted from the nucleus
• The anti-neutrino is the antiparticle of a neutrino
  • Electron anti-neutrinos are produced during β– decay
  • Electron neutrinos are produced during β+ decay

• Although the neutrino has no charge and negligible mass, its existence was hypothesised to account for the conservation of energy in beta decay

• When the number of α particles is plotted against kinetic energy, there are clear spikes that appear on the graph
• This demonstrates that α-particles have discrete energies (only certain values)

 

Alpha particles have discrete energy levels whilst beta particles have a continuous range of energies

• When the number of β particles is plotted against kinetic energy, the graph shows a curve
• This demonstrates that beta particles (electrons or positrons) have a continuous range of energies
• This is because the energy released in beta decay is shared between the beta particles (electrons or positrons) and neutrinos (or anti-neutrinos)
• This was one of the first clues of the neutrino’s existence
• The principle of conservation of momentum and energy applies in both alpha and beta emission