# A1 and A2 Values for Radionuclides

• 1. For a single radionuclide of known identity, the values of A1 and A2 are taken from Table 1 if listed there. The values A1 and A2 in Table 1 are also applicable for the radionuclide contained in (α,n) or (γ,n) neutron sources.
• 2. For any single radionuclide whose identity is known but which is not listed in Table 1, the value of A1 and A2 are determined according to the following procedure.
• (a) If the radionuclide emits only one type of radiation, A1 is determined according to the following method. For radionuclides emitting different kinds of radiation, A1 is the most restrictive value of those determined for each kind of radiation. However, in either case, A1 is restricted to a maximum of 1000 curies (37 TBq). If a parent nuclide decays into a shorter lived daughter with a half-life not greater than 10 days, A1 is calculated for both the parent and the daughter, and the more limiting of the two values is assigned to the parent nuclide.
• (1) For gamma emitters, A1 is determined by the expression:

Where Γ is the gamma-ray constant, corresponding to the dose in roentgens per curie-hour at 1 meter, and the number 9 results from the choice of 1 rem per hour at a distance of 3 meters as the reference dose-equivalent rate.

• (2) For x-ray emitters, A1 is determined by the atomic number of the nuclide:
for Z 55, A1 = 1000 Ci (37 TBq); and
for Z > 55, A1 = 200 Ci (7.4 TBq)
where Z is the atomic number of the nuclide.
• (3) For beta emitters, A1 is determined by the maximum beta energy (E max) according to Table 2; and
• (4) For alpha emitters, A1 is determined by the expression:
A1 = 1000 A3
where A3 is the value listed in Table 3;
• (b) A2 is the more restrictive of the following two values:
• (1) The corresponding A1; and
• (2) the value A3 obtained from Table 3.
• 3. For any single radionuclide whose identity is unknown, the value of A1 is taken to the 2 Ci (74 MBq) and the value of A2 is taken to be 0.002 Ci (74 MBq). However, if the atomic number of the radionuclide is known to be less than 82, the value of A1 is taken to be 10 Ci (370 GBq) and the value of A2 is taken to be 0.4 Ci (14.8 GBq).