Table 7.

Uncertainty budget for ²²⁹Th half-life determination

Component	Comment		Type	ui%2
Activity ratio	Standard uncertainty of combined activity ratio measurements from this study		A	0.48
LTAC 229Th activity	Standard uncertainty of the M solution massic activity		B	0.28
229Th molality	Combined standard uncertainty of the measured 229Th molality		B	0.07
Dilution factor	Standard uncertainty of the dilution factor for production of SRM 4328C from the M solution		B	0.03
Decay interval	Relative uncertainty associated with the interval between the M solution reference date and molality measurements		B	0.00
Relative combined standard uncertainty (uc)			0.56%
229Th half-life (a)		Expanded uncertainty3 (a)
7825		87 (Relative: 1.1%)

The uncertainty estimate for the half-life was calculated in accordance with Taylor and Kuyatt, [20] and GUM protocols [21] using the GUM Workbench software [22]. u_i% represents the relative standard uncertainty for the listed components. The expanded uncertainty (U = k × u_c) for the half-life value is the product of the combined standard uncertainty (u_c) and a coverage factor (k), with k = 2 to achieve an approximately 95% level of confidence