Table 1.

Calculation of the activity per unit mass of the CRM 112-A metal for each uranium isotope, as obtained from the atom percentages given in the CRM 112-A Certificate of Analysis [5] and the DDEP-evaluated half-lives [1]. Numbers in parentheses represent the numerical value of the uncertainty and refer to the corresponding last digits of the quoted result. The atom percent uncertainty is two times the standard uncertainty, as given in the CRM Certificate, while those for the half-life and activity per unit mass are standard uncertainties.

Uranium isotope	Atom percent of isotope (%), I	Half-life (a), T	Activity per unit mass of CRM 112-A (Bg g−1), A
234U	0.005 245 8 (81)	2.455 (6) × 105	1.187 1 (30) × 104
235U	0.72 017 (39)	7.04 (1) × 108	5.683 4 (82) × 102
238U	99.247 48 (39)	4.468 (5) × 109	1.234 4 (14) × 104