The initial step in determining whether the requirements for security-enhanced sources apply to a source is for the licensee to categorise sealed radioactive sources for which they are responsible, in accordance with the Security Code.
The category of a source is determined by the ratio of the activity of the source to the dangerousness (D-value) of the radionuclide. Depending on that ratio, the source is categorised from 1 to 5.
Schedule B of the Security Code sets out D-values for radionuclides and details the methodology for categorising sources; some of the common radionuclides are listed in the table below.
Categorisation thresholds of common radionuclides
These thresholds apply to sources or aggregations of the same radionuclide. Those responsible for sources should apply the formula in Schedule B of the Code to aggregate sources of different radionuclides.
| Radionuclide | Category 1 (TBq) | Category 2 (GBq) | Category 3 (GBq) | Category 4 (GBq) | Category 5 exemption levels (MBq) |
|---|---|---|---|---|---|
|
Am-241 |
60 |
600 |
60 |
0.6 |
0.01 |
|
Am-241/Be |
60 |
600 |
60 |
0.6 |
0.01 |
|
Cs-137 |
100 |
1000 |
100 |
1 |
0.01 |
|
Cf-252 |
20 |
200 |
20 |
0.2 |
0.01 |
|
Co-60 |
30 |
300 |
30 |
0.3 |
0.1 |
|
Cm-244 |
50 |
500 |
50 |
0.5 |
0.01 |
|
Ir-192 |
80 |
800 |
80 |
0.8 |
0.01 |
|
P-32 |
10,000 |
100,000 |
10,000 |
100 |
0.1 |
|
Pu-238 |
60 |
600 |
60 |
0.6 |
0.01 |
|
Po-210 |
60 |
600 |
60 |
0.6 |
0.01 |
|
Ra-226 |
40 |
400 |
40 |
0.4 |
0.01 |
|
Se-75 |
200 |
2000 |
200 |
2 |
1 |
|
Sr-90 |
1000 |
10,000 |
1000 |
10 |
0.01 |