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Ferrous sulphate (Fricke) dosemeter solutions from five laboratories have been intercompared. Differences in their ferric ion yields do not exceed 0.5% and are not statistically significant. For all the solutions precautions were taken to remove impurity effects arising from the sulphuric acid. Spectrophotometers used in these five laboratories for measurement of ferric ion concentrations were also intercompared. Significant differences of over 1% were found between independent determinations of the ferric ion extinction coefficient made on them. Errors in the measurement of are now one of the major contributions to the overall uncertainty in ferrous sulphate dosimetry.
J. Adam Law (Wed,) studied this question.