The categorization of sealed radioactive sources in relation to their potential radiological threat is essential for establishing appropriate security measures and protocols.

The Code of Practice for the Security of Radioactive Sources classifies sealed radioactive sources into 5 categories based on the total radioactivity of a specific isotope, with category 1 being the highest. Sources classified as category 1, 2 and 3 are deemed security enhanced and therefore those require extra security measures to decrease the probability of the unauthorised access to or acquisition of the radioactive source by individuals with malicious intent. When multiple sources are stored in one location, their combined activity level can elevate the overall risk classification. This means that even if individual sources are categorized as lower risk, their total activity might warrant a higher security classification. Licence holders who are authorised to acquire or store security enhanced sources must have an approved Security Plan for every source or for every group of security enhanced sources.