For the categorization of a radioactive source the activity ratio A/D should be calculated. This should be done by taking the activity A of the concerned source (in TBq) and dividing it by the D value. The resulting ratio A/D should then be compared with the values tabulated in the right-hand column of Table 1. Table 2 shows the activity corresponding to a dangerous source (D value) for selected radionuclides used in common practices. The D values for additional radionuclides are specified by the NRRC.
Table 1. Categories for sealed sources used in common practices
For short half-life radionuclides and unsealed sources, the above method for the categorization may be applied, but the NRRC will determine the category of the concerned source on a case by case basis.
For situations in which radioactive sources are in close proximity to each other, such as in manufacturing processes (e.g. in the same room or building) or in storage facilities (e.g. in the same enclosure) the activi-ty in the source shall be aggregated. In such situations, the summed activity of the radionuclide should be divided by the appropriate D value and the calculated ratio A/D compared with the ratios A/D given in Table 1. If sources with various radionuclides are aggregated, then the sum of the ratios A/D should be used in determining the category, in accordance with the formula:
Since this table does not state which dose criteria were used, these D values cannot be used 'in reverse' to derive possible doses from exposure due to sources of known activity.
(a) with the new regulations.