Beta Decay

Beta particles are a form of ionizing radiation made up of high-energy, fast-moving, and electrically-charged subatomic particles. Henri Becquerel is credited with the discovery of nuclear radiation in 1896. In 1898 Ernest Rutherford, working at McGill University in Montreal, discovered that “Becquerel rays”, as they were then known, consisted of both positively-charged and negatively-charged particles, which he named “alpha” and “beta”, respectively, after the first and second letters of the Greek alphabet. In 1900, Becquerel showed that beta particles were identical to electrons, which had recently been discovered by J.J. Thomson. In 1903 Rutherford, still working at McGill University in Montreal, proposed the ground-breaking concepts of “radioactive decay” and “half-life”. In 1908 Rutherford’s revolutionary ideas earned him the Nobel Prize – the first awarded for work performed in Canada.

The production of beta particles is therefore termed “beta decay”. As it turns out, there are two types of beta particles: ß+ and ß-.

β- decay occurs when a neutron in the nucleus of an unstable atom is converted into a proton. During this conversion an electron and an antineutrino are ejected from the nucleus. This type of beta decay is also known as electron emission.  An example of β- decay is

beta1
 

β+ decay, also known as positron emission, is almost the exact opposite. β+ decay occurs when a proton in the nucleus of an unstable atom is converted into a neutron. Typically, when beta decay occurs, a small amount of gamma radiation is also emitted.  An example of β+ decay is

beta2

Beta particles can travel a few metres through the air and can be stopped by a thin sheet of aluminum or a piece of wood a few centimetres thick. However, they do travel fast enough to penetrate clothing and do pose a health risk especially if, like alpha particles, they are inhaled or ingested.

Radioactive isotopes which emit beta particles are called beta emitters. Beta emitters exist in our environment from both natural and man made sources. Some beta emitters such as carbon-14 and potassium-40 exist naturally in your body.

Beta Emitters

Radioactive isotopes which emit beta particles are called beta emitters. Below is list of some beta emitting radioactive isotopes.

  • Carbon-14 is used in carbon dating artifacts and as a medical tracer
  • Cesium-137 is used in brachytherapy to treat various types of cancer and to measure the flow of oil in pipelines.
  • Cobalt-60
  • Hydrogen-3 (tritium)
  • Iodine-129
  • Iodine-131 is used as a medical tracer
  • Nickel-63 is used to detect explosives, and in voltage regulators and current surge protectors in electronic devices.
  • Promethium-147 is used in electric blanket thermostats, and to gauge thickness of thin plastics, thin sheet metal, rubber, textile and paper.
  • Sodium-24 is used to locate leaks in industrial pipelines, oil well studies and in medical diagnostics.
  • Strontium-90 is used as a power source for weather satellites and navigation buoys
  • Sulphur-35 is used in manufacturing sensors and medical treatments.
  • Technetium-99m is used in nuclear medicine as a radioactive tracer
  • Thallium-204 is used to measure the dust and pollutant levels on filter paper, and in gauges used to measure the thickness of plastics, sheet metal, rubber, textiles, and paper.

The beta emitters listed above are commonly used in medical imaging, diagnoses and treatments as well as industrial applications.

Sources:

Human Health Fact Sheet, ANL, October 2001
Radioisotopes Commonly Used in Devices by Industry, USEPA, www.epa.gov/radiation/source-reduction-management/radionuclides.html