Sixteen aliquots of JB-1 with different weights were studied by instrumental neutron activation analysis. It is observed that concentrations of Na, Fe, Sc, U, Th and rare earth elements are reproducible for JB-1 with the sample size of mg level. However, concentrations of Mo, W and Ta show a significant scatter even at 50 mg level. It is, therefore, suggested that chemical standards be used for Mo, W and Ta determination for geological samples, otherwise the rock reference sample, if used as a standard, be checked for the reproducibility of concentrations of these three elements.
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