Radioactive source
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A radioactive source or radiation source is a sample of a radionuclide, usually contained within a radiation-resistant container. It emits ionizing radiation (one or more of gamma rays, alpha particles, beta particles, and neutron radiation), which can be used in medicine for radiation therapy and in industry for industrial radiography, food irradiation, sterilization, disinfestation, crosslinking, and more. Radionuclides are chosen according to the type and character of the radiation they emit, intensity of emission, and the half-life of their decay. Common source radionuclides include cobalt-60,[1] iridium-192,[2] and strontium-90.[3] The activity of a radioactive source is typically measured in Curies, despite NIST strongly advising the use of the Becquerel.[4] A radioactive source typically lasts for between 5 and 15 years before its activity drops below useful levels.[5]
Sealed sources
Many radioactive sources are sealed, meaning they are permanently either completely contained in a metallic capsule or in a tightly bonded solid. Containing capsules are usually made of stainless steel, titanium, platinum or another inert metal.[5] The use of sealed sources removes almost all risk of dispersion of radioactive material into the environment due to mishandling,[6] but the container is not intended to be radiation proof, so further shielding is required for protection.[7] Sealed sources are used in almost all applications where the source does not need to chemically or physically react with anything, including brachytherapy.
Categorisation of sealed sources[8]
Sealed sources are categorised by their activity in relation to a minimum dangerous source (where a dangerous source is one that could cause significant injury to humans). The ratio used is A/D, where A is the activity of the source and D is the minimum dangerous activity.
| Category | A/D |
|---|---|
| 1 | ≥1000 |
| 2 | 10–1000 |
| 3 | 1–10 |
| 4 | 0.01–1 |
| 5 | <0.01 |
Note that sources with sufficiently low radioactive output (such as those used in Smoke detectors) as to not cause harm to humans are not categorised.
Unsealed sources
Unsealed sources are sources that are not in a permanently sealed container, and are used extensively for medical purposes.[9] They are used when the source needs to be dissolved in a liquid for injection into a patient or ingestion by the patient. Unsealed sources are also used in industry in a similar manner for leak detection as a Radioactive tracer.
Disposal
Disposal of expired radioactive sources presents similar challenges to the disposal of other nuclear waste, although to a lesser degree. Spent low level sources will sometimes be sufficiently inactive that they are suitable for disposal via normal waste disposal methods — usually landfill. Other disposal methods are similar to those for higher-level radioactive waste, using various depths of borehole depending on the activity of the waste.[5]
See also
- Common beta emitters
- Commonly used gamma-emitting isotopes
- Geiger counter
- Ionizing radiation
- Neutron source
References
- ↑ "C-188 Cobalt-60 Source". Nordion Inc. Retrieved 22 March 2016.
- ↑ "Iridium-192". Isoflex. Retrieved 22 March 2016.
- ↑ "Radioactive sources: isotopes and availability". Retrieved 22 March 2016.
- ↑ "NIST Guide to the SI, Chapter 5 (paragraph 5.2)". NIST. Retrieved 22 March 2016.
- 1 2 3 Disposal Options for Disused Radioactive Sources (PDF). International Atomic Energy Agency. 2005. ISBN 92-0-100305-6. ISSN 0074-1914.
- ↑ "Implementation of the Control of High-activity Sealed Radioactive Sources and Orphan Sources (HASS) directive for nuclear licensed sites". Retrieved 22 March 2016.
- ↑ "Disused Sealed Source Managment". International Atomic Energy Agency. Retrieved 22 March 2016.
- ↑ Radiation protection and safety of radiation sources : International basic safety standards (PDF). Vienna: International Atomic Energy Agency. 2014. ISBN 978-92-0-135310-8. ISSN 1020-525X.
- ↑ "Radiation Protection Glossary". Retrieved 22 March 2016.