Understanding Radiation

Glossary of Common Radiation Terms

Acute Health Effect – The effect on health that is quickly seen after exposure to high levels of radiation. Such effects include skin burns and acute radiation syndrome (see ‘Radiation Sickness’)

Alpha (α) particle – A positively charged particle made up of two neutrons and two protons emitted by certain radioactive nuclei. Alpha particles have little penetration power and are easily stopped by a sheet of paper or outer layer of skin. However, alpha emitting materials are harmful to health if they enter the body by inhalation or ingestion of food and water.

Background Radiation – Radiation from natural sources such as radionuclides in the soil or cosmic radiation from outer space.

Beta (β) particle – An electron or positron emitted by certain radioactive nuclei and is more penetrating than alpha particles. A sheet of aluminium of a few millimetres thick can stop beta particles. They can be lethal, depending on the amount received.

Deterministic Effect – The effect on health that is directly related to the amount of radiation dose received. The more radiation a person receives, the more severe the health effect. However, a threshold must be exceeded in order for the health effect to first appear. This is sometimes referred to as a ‘non-stochastic effect’.

Dirty Bomb – A device designed to spread radioactive materials by explosion. A dirty bomb kills or injures people through the initial blast and spreads radioactive material over a large area. See also “Radiological Dispersal Device”

Dose (Absorbed) – The concentration of energy deposited in human tissue as a result of an exposure to ionising radiation. The unit of measurement for absorbed dose is the milligray (mGy)

Dose (Effective) – A measurement developed by the International Commission on Radiological Protection (ICRP) for use in radiation protection. It is a calculation using a complex equation that takes three factors into account: 1) the absorbed dose to all organs of the body, 2) the relative harm level of the radiation, and 3) the sensitivities of each organ to radiation. This calculation is made for a reference population and is not intended to be applied to a specific individual. The unit of measurement for effective dose is milliSievert (mSv).

Dose (Equivalent) - The impact that a type of radiation has on human tissue. The unit of measurement for equivalent dose is milliSievert (mSv)

Dose (Radiation) – Radiation absorbed by a person’s body.

Dose Rate – The radiation dose delivered per unit of time.

Gamma (γ) ray – High-energy electromagnetic radiation emitted by certain radioactive nuclei. Due to their high energy, these rays are very penetrating and can pass right through the human body. Dense materials such as lead or concrete are more effective in absorbing these rays. Gamma rays are potentially lethal depending on the dose.

Ionising Radiation (IR) – Ionising radiation possesses enough energy to knock electrons out of atoms and poses a health risk by damaging tissue and DNA in genes. Long-term exposure to ionising radiation at high levels can harm people’s health.

Naturally Occurring Radioactive Material (NORM) – Radioactive material that contains no significant amounts of radionuclides other than naturally occurring radionuclides.

Neutron – A small particle which does not carry any electric charge. Hydrogen-rich materials such as water or paraffin can shield against these highly penetrating particles.  

Non-Ionising Radiation (NIR) – Radiation that has lower energy levels than ionising radiation. Non-ionising radiation moves atoms in a molecule around or causes them to vibrate but does not have enough energy to remove electrons from atoms. Examples include radio waves, microwaves, visible light and infrared from a heat lamp.

Non-stochastic Effect – See ‘Deterministic Effect’.

Radiation Sickness – Exposure to a very high level of radiation over a short period of time can cause symptoms such as nausea and vomiting and can sometimes result in death. Radiation sickness is rare and comes from extreme events like a nuclear explosion or accidental handling of a highly radioactive source.

Radiological Dispersal Device (RDD) – A device that disperse radioactive material by explosion or mechanical means.

Radiological Exposure Device (RED) – A device intended to expose people to significant doses of radiation without their knowledge. An RED may be constructed from partially or fully unshielded radioactive material and could be hidden from sight in a public space, exposing those who sit or pass close by.

Radionuclides of Natural Origin – Radionuclides that occur naturally on Earth in significant quantities. It is usually used to refer to the primordial radionuclides K-40, U-235, U-238, Th-232 and their radioactive decay products.

Stochastic Effect – A radiation induced health effect, of which the probability of occurrence is greater for a higher radiation dose; and the severity is independent of dose. Stochastic effects generally occur without a threshold level of dose. Examples include cancers (e.g. leukaemia). 

X-rays – X-rays, like gamma rays can travel long distances through air and most other materials. Dense materials such as lead or concrete are more effective in absorbing these rays.