Reports on Lost or Stolen Sealed Sources and Radiation Devices

Appendix

Categorization of sources

Radioactive sealed sources are used throughout the world in medicine, industry, agriculture, research and education, and vary widely in radiological risk.¹ In 2005, the IAEA published a risk-based ranking of radioactive sources and practices, which uses five categories. The category assigned to each practice or radioactive nuclear substance (which the sealed source is made of) takes into consideration factors such as the radiological risk associated with the source, the nature of the work (or application for which the source is used), the mobility of the source, experience from reported accidents, and typical vs. unique activities within an application. These factors were used to assign sources and practices to one of five categories. Category 1 sources are considered to pose the greatest risk to human health (if not managed safely and securely), while Category 5 sources pose the lowest risk.

¹ IAEA, Categorization of Radioactive Sources, RS-G-1.9, (2005), p.1

Category 1 sources are classified as “personally extremely dangerous”

Category 1 (Very High-risk)

This amount of radioactive material, if not safely managed or securely protected, would be likely to cause permanent injury (in some cases, be fatal) to a person who handled it, or was otherwise in contact with it for a period of a few minutes (or be fatal if close to it in an unshielded manner for a few minutes to an hour).² Category 1 sources are associated with licensed activities to which the CNSC Class II Nuclear Facilities and Prescribed Equipment Regulations mostly apply.

Examples of a Category 1 source usage:

Self Shielded Irradiators: Gamma sources are used in these irradiators for experimental purposes or as a means of sterilization. Gamma irradiation kills bacteria by breaking down bacterial DNA and inhibiting cell division. Blood products, for example, are sterilized in self-shielded irradiators.

Image 1: Cobalt-60 Gammacell

Gamma Knife Radiosurgery: An advanced form of surgery, performed with highly focused beams of radiation. As many as two hundred and one radioactive sealed sources create intersecting beams of gamma radiation which deliver a concentrated dose of radiation to a precise area of the brain. These radiation beams form the “knife”.

Image 2: Elekta Gamma Knife

Image 3: Gamma Knife in use

Radioactive Source Teletherapy: External beam radiotherapy otherwise known as “teletherapy” is the most frequently used form of radiotherapy. Radiotherapy is the medical use of radiation (produced by a radioactive sealed source mounted inside the machine) as part of cancer treatment, to control malignant cells.

Image 4: Co-60 Teletherapy

² IAEA, Categorization of Radioactive Sources, RS-G-1.9, (2005), Table 3

Category 2 sources are classified as “personally very dangerous”

Category 2 (High-risk)

This amount of radioactive material, if not safely managed or securely protected, could cause permanent injury to a person who handled it, or was otherwise in contact with it for a short period of time (minutes to hours) – or be fatal if close to it in an unshielded manner for a few days. Category 2 sources are associated with licensed activities to which the CNSC Nuclear Substances and Radiation Devices Regulations mostly apply.

Example of a Category 2 source usage:

Industrial radiography is a non-destructive testing (NDT) application that uses gamma radiation from a highly radioactive source, and photographic film, for the detection of internal physical imperfections (such as voids, cracks, flaws, segregations, porosities and inclusions) in pressure vessels, pipelines, ships and reactor components. Radiography produces images on photographic film, similar to X-ray images, that show varying densities according to the amount of radiation absorbed in the material.

Image 5: Industrial radiography camera which contains the radioactive sealed source

Image 6: NDT pipeline inspection, using industrial radiography equipment

Category 3 sources are classified as “personally dangerous”

Category 3 (Moderate-Risk)

This amount of radioactive material, if not safely managed or securely protected, could cause permanent injury to a person who handled it, or was otherwise in contact with it, for some hours. It could possibly — although it is unlikely — be fatal to be close to this amount of unshielded radioactive material for a period of days to weeks.³ Category 3 sources are associated with licensed activities to which the CNSC Nuclear Substances and Radiation Devices Regulations mostly apply.

Examples of a Category 3 source usage:

Industrial gauges: These gauges are usually installed in fixed positions for measuring and process control purposes. These include density gauges, level gauges, belt mass meters and thickness gauges. The radioactive sealed source is mounted inside the gauge and projects a radiation beam, through the material, which is picked up by a detector to provide a measurement.

Image 7: Industrial fixed gauge

High dose rate (HDR) brachytherapy is the placement of a small, highly radioactive sealed source, directly into cancerous tissues, for a short period of time. The procedure is sometimes guided by ultrasound or 3D computerized mapping techniques. Brachytherapy delivers a concentrated dose of radiation to cancerous tissue from within.

Image 8: HDR Brachytherapy

³ IAEA, Categorization of Radioactive Sources, RS-G-1.9, (2005), Table 3

Category 4 sources are classified as “unlikely to be dangerous”

Category 4 (Low-risk)

It is very unlikely that anyone would be permanently injured by this amount of radioactive material. However, this amount of unshielded radioactive material, if not safely managed or securely protected, could possibly — although it is unlikely — temporarily injure someone who handled it or was otherwise in contact with it, or who were close to it for a period of several weeks.⁴ Category 4 sources are associated with licensed activities to which the CNSC Nuclear Substances and Radiation Devices Regulations mostly apply.

Example of Category 4 source usage:

Low dose rate industrial gauges, such as moisture/density gauges, are used to measure the density of asphalt, soil, aggregate or concrete, as well as the moisture content of soil or aggregate.

Image 9: Portable gauge

Image 10: Portable gauge in use

⁴ IAEA, Categorization of Radioactive Sources, RS-G-1.9, (2005), Table 3

Category 5 sources are classified as “not dangerous”

Category 5 (Very Low-risk)

No one could be permanently injured by this amount of radioactive material.⁵ Category 5 sources are associated with licensed activities to which the CNSC Nuclear Substances and Radiation Devices Regulations mostly apply.

Examples of a Category 5 source usage:

Electron capture detector Ni-63 sources, used in gas chromatography instruments. They are used to detect minute amounts of chemical compounds, such as halogenated organic chemicals in environmental samples. Pesticide levels in foodstuffs, for example, are measured with these detectors.

Image 11: Electron Capture Detector

Low dose rate (LDR) brachytherapy involves exposure to small radioactive sealed sources for hours to days. Ocular melanoma is one example of a tumor that can be treated with LDR brachytherapy. In another example, radioactive seeds of iodine-125 are surgically implanted to treat prostate cancer.

Image 12: LDR Brachytherapy

⁵ IAEA, Categorization of Radioactive Sources, RS-G-1.9, (2005), Table 3