Table 3.

Uncertainty assessment for the massic activities of ²³⁴U, ²³⁵U, and ²³⁸U in in the natural uranium solution standard SRM 4321d, where u in percent is the relative standard uncertainty for each component. All uncertainty components were evaluated by Assessment Type B, which denotes an evaluation by methods other than statistical methods [6, 7].

Uncertainty component		u (%)
		234U	235U	238U
1	Uranium mass fraction in CRM 112-A, from CRM 112-A Certificate [5]	0.003	0.003	0.003
2	Isotopic uranium atom fraction in CRM 112-A, from CRM 112-A Certificate [5]	0.077	0.027 1	0.000 20
3	Half-life [4] used for conversion of number of atoms to activity	0.244	0.142	0.112
4	Mass of CRM 112-A uranium metal used	0.05	0.05	0.05
5	Quantitative dissolution of metal	0.05	0.05	0.05
6	Mass of SRM 4321d master solution	0.005	0.005	0.005
Relative combined standard uncertainty, uc		0.261	0.153	0.123
Relative expanded uncertainty (k = 2), U		0.52	0.31	0.25