The Type A quantity of any particular material is the maximum quantity of that material that the regulations deem to be sufficiently non-hazardous to be transported in a Type A packaging. Note that Type A refers to the total activity rather than to the specific activity. For example, if some quantity of material exceeds the amount that may be transported in a Type A packaging, it is possible that this quantity may be transported in Type A packagings if it is subdivided into smaller quantities.
Type A quantities for various radionuclides are defined by tables in both IAEA SS6 and in 10 CFR 71. A distinction is made between tabulated A1 values and A2 values with A1 applying to materials that satisfy "special form" requirements and A2 applying to those that do not. (Note: the 1 and 2 in A1 and A2 are usually shown as subscripts, as A1 and A2, but I will ignore this detail throughout to simplify the text and improve readability.) "Special form" refers to materials that are not dispersible as demonstrated by a series of specified tests. In many cases the A1 values are the same as the A2 values, however in some cases, particularly for heavy metals, they are as much as 10,000 times higher. The values are given as the number of Ci and TBq of that material that constitute a Type A quantity. The quantity can readily be converted to grams by dividing by the activity per gram which is tabulated in the same table in 10 CFR 71 and in a corresponding table in IAEA SS37.
It is conventional to express a quantity of material as being "a certain number of A2" (or A1 if special form). It would be more logical to use the terminology "a certain number of Type A quantities" or "a certain number of A" however the form "the contents is 7.3 A2" is generally used. In any case the A1 or A2 measure can be considered a consistent unit of radiological hazard; whereas, as noted previously, the Ci cannot.
Type A quantity examples