Table 8.

Atom percents and atomic weights for the three standard samples

		Overall limit of errora	Uncertainty components
			Mass spectrometric analytical error	Possible systematic error in chemical analysis	Possible systematic error in composition of separated isotopes
Common Lead (SRM 981) Atomic weight 207.2152		±0.00015	±0.00004	±0.00003	±0.00008
Atom percent:
204Pb	1 4245	±0.0012	±0.0005	±0.0002	±0.0005
206Pb	24 1447	±0.0057	±0.0014	±0.0012	±0.0031
207Pb	22 0827	±0.0027	±0.0019	±0.0002	±0.0006
208Pb	52 3481	±0.0086	±0.0028	±0.0016	±0.0042
Equal-Atom Lead (SRM 982) Atomic weight 206.9429		±0.00014	±0.00003	±0.00003	±0.00008
Atom percent:
204Pb	1 0912	±0.0012	±0.0008	±0.0001	±0.0003
206Pb	40.0890	±0.0072	±0.0015	±0.0016	±0.0041
207Pb	18 7244	±0.0023	±0.0022	±0.0000	±0.0001
208Pb	40 0954	±0 0077	±0.0019	±0.0016	±0.0042
Radiogenic Lead (SRM 983) Atomic weight 206.0646..		±0.00009	±0.00006	±0.00001	±0.00002
Atom percent:
204Pb	0 0342	±0.0020	±0.0020	±0.0000	±0.0000
206Pb	92 1497	±0.0041	±0.0029	±0.0003	±0.0009
207Pb	6 5611	±0.0025	±0.0017	±0.0002	±0.0006
208Pb	1 2550	±0.0022	±0.0018	±0.0001	±0.0003
Nuclidic Masses: 203.973044, 205.974468, 206.975903, 207.976650

^aThe overall limit of error is the sum of the 95 percent confidence limits for the ratio determinations and the terms covering effects of known sources of possible systematic error.