Table 1.

Measured ²³¹Pa/²³⁵U mass ratios and production dates

Sample	231Pa/235U mass ratio	Standard uncertainty	231Pa/235U model age (year)	Expanded uncertainty (year, k = 2)	Measured 231Pa/235U model production date
CRM 125-A #1	2.278 × 10−8	4.2 × 10−10	23.54	0.88	26 December 1994
CRM 125-A #2	2.269 × 10−8	3.2 × 10−10	23.45	0.67	27 January 1995
IRMM1000 #1	5.926 × 10−9	1.2 × 10−10	6.12	0.24	27 May 2012
IRMM1000 #1	6.006 × 10−9	1.0 × 10−10	6.21	0.21	24 April 2012
U100 #1	5.619 × 10−8	7.5 × 10−10	58.1	1.6	03 June 1960
U100 #2	5.813 × 10−8	9.6 × 10−10	60.1	2.0	04 June 1958
U630 #1	2.815 × 10−8	4.0 × 10−10	29.09	0.83	07 June 1989
U630 #2	2.805 × 10−8	3.8 × 10−10	28.99	0.79	14 July 1989