OPTIMIZATION OF MULTICOLLECTOR ISOTOPE-RATIO MEASUREMENT OF STRONTIUMAND NEODYMIUM

For isotope-ratio analyses of Sr and Nd whose precisions are constrain ed by amplifier and ion-counting noise, significant improvements in ef ficiency/precision can be realized by appropriate choices of peak vs. background measurement times, peak-jumping modes, and ratios for fract ionation normalization. For Nd, theoretical limits on internal precisi on predict that the time-efficiency of dynamic analyses should be simi lar to that of static in most cases (slightly better in others), and t hat for Sr, dynamic analyses should be actually more efficient than st atic. Equations for the optimum mix of background times and peak-top t imes are given.