PARTICLES AND RADIATION

Particles, Anti-particles and Photons

Particles, Anti-particles and Photons

All particles have an anti-particle which corresponds to it:

  • the anti-particle of an electron is a positron
  • the anti-particle of a proton is an anti-proton
  • the anti-particle of a neutron is an anti-neutron
  • the anti-particle of a neutrino is an anti-neutrino
Particle Symbol Charge Rest mass/MeV
ElectronPositron e- ?- ee+ ?+ ? -+ 0.5109990.510999
ProtonAnti-proton pp +- 238.257238.257
NeutronAnti-neutron nn 00 939.551939.551
NeutrinoAnti-neutrino vv 00 00

Pair production and annihilations

When a particle and an anti-particle meet, they annihilate one another. In this process, their mass is converted into energy which takes the form of photons.

Annihilation is an example of mass being converted into energy. However, it’s also possible for the reverse to occur: high energy photons are able to create a particle and its anti-particle. This is known as pair production. For example, it is possible for a gamma photon which contains enough energy to production both an electron and its positron.

Photons

Electromagnetic radiation, which includes visible light, x-rays and gamma rays, consist of wave properties. However, they can also act like particles called photons.

The energy (E) a photon possess is dependent on its frequency (f):

E = hf = hc / ?

In which:

  • E = the energy of the photon in joules (J)
  • h = the Plant constant (6.63 x 10-34Js)
  • f – frequency in hertz (Hz)
  • c = speed of light (3.00 x 108 metres per second (ms-1))
  • ? = wavelength in metres (m)