Radioactive Material

Primary reference(s)

IAEA, 2018. IAEA Safety Glossary: Terminology used in Nuclear Safety and Radiation Protection, 2018 edition. International Atomic Energy Agency (IAEA). Accessed 15 November 2019.

Additional scientific description

Radioactive materials (natural and human-made) are widely used in industry, medicine and research. There are various types of ionising and non-ionising radiation, each having different characteristics (IAEA, 2021):

• Alpha-radiation: consists of heavy, positively charged particles emitted by atoms of elements such as uranium and radium. Alpha-radiation cannot penetrate skin and can be stopped by a thin paper sheet. However, alpha-emitting radioactive material entering the body by breathing, eating, or drinking, can affect organs and tissues and cause biological damage.
• Beta-radiation: consists of electrons, is more penetrating than alpha-radiation and can pass through the skin surface. In general, a sheet of aluminium a few millimetres thick will stop beta-radiation.
• Gamma-rays: electromagnetic radiation similar to X-rays, light, and radio waves. Depending on their energy, gamma-rays can pass right through the human body, but not through a concrete wall or lead.
• Neutrons: uncharged particles that do not produce ionisation directly. Nevertheless, their interaction with other atoms can give rise to alpha-radiation, beta-radiation, or gamma-rays in the matter they traverse, which then produce a subsequent ionisation. Neutrons are highly penetrating and can only be stopped by thick masses of concrete, water or paraffin. 

Depending on the magnitude of exposure, the radioactive substance may become a hazard to human health; as such it is subject to regulatory control by national laws and national regulatory authorities. Radioactive material may also be hazard to animal health, other forms of life and the environment (IAEA, 2018).

Metrics and numeric limits

Although the presence of radiation cannot be seen or felt, it can be detected and measured in extremely small quantities with simple radiation measuring instruments. The biological effects of ionising radiation vary with the type and amount of energy. A measure of the risk of biological harm is the dose of radiation that the tissues receive. The unit of absorbed radiation dose is the Sievert (Sv). One Sievert (1 Sv) is a large quantity of radiation. The whole-body dose of 2.5 Sv can be lethal without medical intervention. Radiation doses are generally in the order of milli-Sievert (mSv) or micro-Sievert (μSv). For example, exposure due to all natural radiation sources amounts to about 2.4 mSv per year, while one chest X-ray amounts to about 0.2 mSv (IAEA, 2021).

Radiation dose defines the level of risk for human health. To accurately assess the dose from an exposure resulting from an emergency situation, multiple factors are taken into account: the amount of radioactive material released into the environment (measured in Becquerels, Bq), the exposure rates per unit of time, the duration of exposure, and the pathways of exposure, etc. In addition, the level of risk will depend on the individual exposed (e.g., young children, pregnant women and their foetuses and lactating mothers are most vulnerable to radiation risk and should be given priority during response to a radiation emergency) (IAEA, 2021).

The severity of a radiation emergency is identified by the International Nuclear and Radiological Event Scale (INES) as demonstrated in the graphic below (IAEA, no date). INES is a standard tool for communicating the magnitude of nuclear and radiological events in a consistent manner (IAEA, no date).

Examples of drivers, outcomes and risk management

Exposure to radiation may be external, internal, or combined, and can occur through various exposure pathways.

External exposure may occur near an unshielded radioactive source or when airborne radioactive material (such as dust, liquid, or aerosols) is deposited on skin or clothes. This type of radioactive material can often be removed from the body by simply washing (IAEA, 2021).

Internal exposure to ionising radiation occurs when a radionuclide is inhaled, ingested or otherwise enters into the bloodstream (e.g., by injection or through wounds). Internal contamination with most radionuclides needs medical intervention to remove radionuclides from the body (IAEA, 2021).

Exposure to radiation can be classified into three exposure situations: planned exposures (occupational and medical exposures); existing exposures (natural sources such as radon gas or residual radiation from past accidents or industrial activities); and emergency exposures (radiological and nuclear emergencies, accidents in transport, medicine, research, or even malicious acts involving radioactive material) (IAEA, 2021).

Types of emergencies involving radioactive material range from a small-scale radiological incident involving a lost or stolen industrial radioactive source, over-exposure of a person in an occupational or medical setting, or as a result of a transportation incident; to a large-scale nuclear emergency at a nuclear installation such as a nuclear power plant or a research reactor, or a detonation of a military or improvised nuclear device (IAEA, 2021). Examples of nuclear emergencies are nuclear bomb detonations in Japan at the end of the Second World War; the Three Mile Island and Chernobyl nuclear power plant accidents; and the Great Eastern Japan Earthquake which generated a tsunami and resulted in the Fukushima Daiichi nuclear power plant accident.

Protective actions to prevent or reduce radiation exposure in the case of a radiation emergency situation depend on the type of emergency and may include: taking shelter; evacuation or even permanent relocation from an affected area; restriction of consumption of contaminated food or water; administration of iodine thyroid blocking (in the case of radioactive iodine release); monitoring and measuring radiation in affected people and the environment; securing radioactive sources and cleaning up affected areas; as well as providing information, risk communication, psychological support, medical care and long-term follow-up to those in need (IAEA, 2021).

Other risk management measures include (IAEA, 2021):

• Safe siting, design and construction of nuclear power plants as well as controls and back up measures for their safe operation and radioactive waste management and isolation from the geoenvironment.
• Controls, equipment and training to protect personnel working with radioactive sources.
• Security measures to control access to supply and use of radiation sources.
• Facility, local and national multisectoral radiation emergency response plans for a range of scenarios from low-level exposure to a significant release of radioactivity.
• Effective risk communication which is essential to the public and emergency responders.