Normalization of a liquid scintillation counter is done using unquenched sealed standards of 14C, tritium and background supplied by a commercial company (e. g. Packard Instrument Co.) The samples and standards are usually counted for a preset time of 50 min and the whole batch is cycled 10 times. Thus, each sample/standard is counted for a total time of 500 min (the sample counting time and the number of cycles can be adjusted as per requirement). The samples with higher counts can be counted for shorter times and for fewer repeat cycles). The data are statistically evaluated by applying Chauvenet’s criterion and rejecting outliers. This is followed by the calculation of the mean background count rate, the net mean count rate of the standard and the net count rates of unknown samples.

Uncertainty in the tritium activity is calculated by combining the uncertainties of all the factors involved (net counts per minute of counting standard, activity of counting standard, net counts per minute of sample, weights and decay correction) and using the error propagation law.