Requirements for determining A1 and A2 values for radionuclides and for the listing of radionuclides on shipping papers and labels.

(a) Values of A1 and A2 for individual radionuclides that are the basis for many activity limits elsewhere in this subchapter are given in the table in § 173.435.

(b) For individual radionuclides whose identities are known, but which are not listed in the table in § 173.435, the determination of the values of A1 and A2 requires approval from the Associate Administrator except that the values of A1 and A2 in table 10 may be used without obtaining approval from Associate Administrator.

(c) In calculating A1 and A2 values for a radionuclide not listed in the table in § 173.435, a single radioactive decay chain in which the radionuclides are present in their naturally-occurring proportions, and in which no daughter nuclide has a half life either longer than 10 days or longer than that of the parent nuclide, will be considered as a single radionuclide, and the activity to be taken into account and the A1 or A2 value to be applied will be those corresponding to the parent nuclide of that chain. Otherwise, the parent and daughter nuclides will be considered as a mixture of different nuclides.

(d) Mixtures of radionuclides whose identities and respective activities are known, must conform to the following conditions:

(1) For special form Class 7 (radioactive) material:

ER28SE95.006

Where B(i) is the activity of radionuclide i and A1 (i) is the A1 value for radionuclide i;

or

(2) For other forms of Class 7 (radioactive) material, either—

ER28SE95.007

Where B(i) is the activity of radionuclide i and A2(i) is the A2 value for radionuclide i;

or

ER28SE95.008

where f(i) is the fraction of activity of nuclide i in the mixture and A2(i) is the appropriate A2 value for nuclide i.

(e) When the identity of each nuclide is known but the individual activities of some of the radionuclides are not known, the radionuclides may be grouped and the lowest A1 or A2 value, as appropriate, for the radionuclides in each group may be used in applying the formulas in paragraph (d) of this section. Groups may be based on the total alpha activity and the total beta/gamma activity when these are known, using the lowest A1 or A2 values for the alpha emitters or beta/gamma emitters, respectively.

(f) Shipping papers and labeling. (1) For mixtures of radionuclides, the radionuclides (n) that must be shown on shipping papers and labels in accordance with §§ 172.203 and 172.403 of this subchapter, respectively, must be determined on the basis of the following formula:

ER28se95.009

Where n + m represents all the radionuclides in the mixture, m are the radionuclides that do not need to be considered, ai is the activity of radionuclide i in the mixture, and Ai is the A1 or A2 value, as appropriate for radionuclide i.

(g) Table 10 is as follows:

Table 10—General Values for A1 and A2 Contents A1 (TBq) (Ci) A2 (TBq) (Ci) Only beta or gamma emitting nuclides are known to be present 0.2 5 0.02 0.5 Alpha emitting nuclides are known to be present or no relevant data are available 0.10 2.70 2×10−5 5.41×10−4

[Amdt. 173-244, 60 FR 50307, Sept. 28, 1995, as amended at 63 FR 52849, Oct. 1, 1998; 66 FR 45184, 45379, Aug. 28, 2001]