Evaluation of statistical control charts for on-line radiation monitoring

Statistical control charts are presented for the evaluation of time series radiation counter data from flow cells used for monitoring of low levels of ⁹⁹TcO₄⁻ in environmental solutions. Control chart methods consisted of the 3-sigma (3σ) chart, the cumulative sum (CUSUM) chart, and the exponentially weighted moving average (EWMA) chart. Each method involves a control limit based on the detector background which constitutes the detection limit. Both the CUSUM and EWMA charts are suitable to detect and estimate sample concentration requiring less solution volume than when using a 3σ control chart. Data presented here indicate that the overall accuracy and precision of the CUSUM method is the best.