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Sealed Radioactive Sources: Uses and Risks

Radiation occurs when unstable isotopes of elements release excess energy as invisible waves or particles. Depending on the amount of energy released, these waves or particles are able to penetrate solid matter to varying degrees. Because of these unique properties, radiation has many diverse uses such as:

killing bacteria in commercially packaged food and medical equipment
diagnosing disease with pharmaceuticals labelled with radioactive elements
treating cancer and other diseases
mapping underground sources of water and prospecting for oil and gas reserves
checking levels or density in manufacturing processes

Two broad types of devices exist: those that generate radiation and those that are themselves radioactive. Devices capable of generating radiation include particle accelerators and X ray machines. When the power supply is cut, however, these devices produce no radiation. Other devices contain materials that are radioactive. These devices always produce radiation, but the intensity of the radiation will decrease naturally over time.

A sealed radioactive source, typically called a sealed source, refers to radioactive material that has been sealed inside a capsule or is permanently bonded in a solid form. Sealed sources within devices are commonly used to deliver a defined dose of radiation, such as that used in cancer therapy or in irradiators that sterilize food and medical equipment. But there are also other uses such as: in industrial gauges, in radioisotope thermoelectric generators used to provide electric power in remote areas, in gamma radiography to check welds on pipelines, and in well logging sources used to explore for coal, oil, and natural gas.

Nuclear materials (such as enriched uranium and plutonium) can produce a self-sustaining nuclear fission reaction and are radioactive, but they are not normally used in sealed sources. The radioactive materials in a sealed source (cobalt, caesium, iridium, etc.) on the other hand, are not capable of fission; and the amount of radiation they emit decreases over time.

Sealed radioactive sources within devices, when used as intended, are designed to limit radiation exposure to users. Despite their design safety features, some sealed source devices may produce a potentially lethal amount of radiation if used improperly. People using sealed source devices must be trained and knowledgeable about their proper, safe and secure use. In untrained hands, such devices can injure and kill. Malevolent acquisition and use of radioactive sources may cause radiation exposure or dispersal of radioactive material into the environment. Such an event could cause significant social, psychological and economical impacts.

If a source becomes too weak for its use, it does not mean that the source is safe. Many accidents have resulted from sources that are no longer being used for their original purpose.

The relative risk for sources has been categorized by their potential to cause serious health effects.

Category 1 sources could lead to the death or permanent injury of individuals who are in close proximity to the source for a short period of time (minutes to hours). Category 1 sources include: radioisotope thermoelectric generators, irradiators, teletherapy machines, and fixed multi-beam teletherapy machines.

Category 2 sources could lead to the death or permanent injury of individuals who are in close proximity to the source for a longer period of time than for Category 1 sources. Category 2 sources include: industrial gamma radiography equipment and high/medium dose-rate brachytherapy.

Category 3 sources could lead to the permanent injury of individuals who are in close proximity to the source for a longer period of time than Category 2 sources. Sources in Category 3 could, but are unlikely to, lead to fatalities. Category 3 sources include: fixed industrial gauges (level gauges, dredger gauges, conveyor gauges, and spinning pipe gauges) and well logging gauges.

Category 4 sources could lead to the temporary injury of individuals who may be in close proximity to the source for a longer period of time than Category 3 sources. Permanent injuries are unlikely. Category 4 sources include: low dose-rate brachytherapy sources, thickness gauges, portable gauges, and bone densitometers.

Category 5 sources could, but are unlikely to, cause minor temporary injury of individuals. Category 5 sources include X ray fluorescence devices, static eliminators, and electron capture devices.

Categorization of sources

Physical security measures should be implemented for all sources to avoid the possibility of theft. A graded approach needs to be taken with the most dangerous sources (categories 1–3) to assure their safe and secure use and storage.

Issues for Government Agencies

Sealed Radioactive Sources: Uses and Risks