Fig. 1.

Results obtained from the evaluation of four favorable Zn double-spike compositions with the MATLAB error minimization code of Rudge et al. [29]. The curves denote the uncertainty in the natural fractionation factor α as a function of the proportion of double spike in the spike sample mixture. The results indicate that the double spike used in the present study (with ⁶⁴Zn/⁶⁷Zn = 2.51) can be used over a wide range of spike sample ratios and yields only marginally less precise results than alternative compositions