Beta particles have been identified as fast-moving electrons originating from the nucleus of an atom.
Mass:
As beta particles are electrons they therefore have a mass of 9.12 x 10{U-31} kg.
Charge:
As they are electrons each particle has an electric charge of 1.6 x 10{U-19} coulombs or -e.
Range:
Beta particles have a range of a few metres in air, but they are easily stopped by a few millimetres of aluminium. The particles do not all possess the same quantity of energy as they have a wide range of speeds, although most are emitted at speeds close to the speed of light. Their ionising power is much lower than that of alpha particles, largely due to their much smaller size.
Behaviour:
Beta particles can be deflected by both magnetic and electric fields. In the case of electric fields they will be attracted by the positive and repelled by the negative. In magnetic fields they deflect at right angles to the field according to Fleming's Left-hand Rule.
(2) Detection:
Beta particles can be detected in a variety of ways.
Scintillations: if beta particles strike a surface coated with certain zinc or barium compounds then fluorescence (glowing) occurs at the point at which the particles hit. The particles can be detected by observation, but it is also possible for the quantity of light energy given off to be measured, thus providing an accurate means of measuring the radiation.
Cloud chambers: beta particles can cause ionisation of gases, that is, electrons can be removed from atoms. Ions (electrically-charged particles) are therefore formed. If these ions are produced in an atmosphere rich in water vapour then droplets of water appear where the ions are produced. The path of the beta particles therefore becomes visible.
Geiger-Muller tube and ratemeter: a suitable G-M tube can be used to detect beta particles. Beta particles entering the tube cause particles of the gas inside to become ionised, that is, they become electrically charged. The charged particles are then detected inside the G-M tube, amplified and sent to a suitable ratemeter which displays the number of ionisations occurring as a measure of the intensity of the radiation.
Photographic film is affected by beta particles. Upon development, the film would appear darker; the intensity of the 'darkness' depends upon the intensity of the radiation striking it. A version of this type of detector was used for personal-dose measurement in the nuclear industry.
(3) General:
The electrons causing beta decay of atoms come from the nucleus of the atom; they are not those that are travelling around the nucleus. When a beta particle is emitted it would appear that a neutron changes into a proton with the electron being emitted as the beta particle. This can be simply described as a neutron becoming a proton as it gives out an electron. The production of an additional proton has an effect on the remaining atomic structure. You can find out about this in the 'Isotopes' section.
Beta particles are emitted at speeds close to the speed of light, which is 3 x 10{U8} metres per second.
(4) Discovery:
While radioactivity has been known about and studied for many years it was not until 1899 that scientists realised there were different kinds of radiation. In that year Ernest Rutherford called the more penetrating particles, beta, and the less penetrating particles, alpha.
(5) Biological effects:
Beta particles do not have a great penetrating power and are stopped by a few millimetres of body tissue. Therefore, it is not likely that external sources of beta particles will affect internal organs. However, they can have an effect on the skin and other 'close to the surface' tissue, producing burn-like damage. They can also change cells, causing malformation of subsequently divided cells. The male reproductive organs can be damaged by beta particles causing sterilisation.
Greater radiation damage can occur with the introduction into the body of beta-emitting materials. Intake is most likely to be through breathing in dust particles containing radioactive material. With intake of this nature cells can become cancerous and tumours can form. In extreme cases cancerous cells can be moved around the body, giving rise to the danger of extensive tumour development.
(6) Applications:
Medical applications for both diagnosis and treatment.
