Implementation of an MDA algorithm with Systematic Uncertainties for Non-Destructive Assay

Year
2019
Author(s)
John M. Kirkpatrick - Mirion Technologies (Canberra), Inc.
Patricia McClay - Mirion Technologies (Canberra), Inc.
Ludovic Bourva - Mirion Technologies (Canberra), Inc.
Albert Joseph - Mirion Technologies (Canberra), Inc.
Patrick Chard - Mirion Technologies (Canberra), Inc.
Jas Singh - Mirion Technologies (Canberra), Inc.
Abstract
A new algorithm for calculating the Minimum Detectable Activity (MDA) which also accounts for the effects of the Total Measurement Uncertainty (TMU) has recently been implemented in Canberra’s NDA 2000 Non-Destructive Assay Software. The new algorithm is consistent with the goals of the ISO 11929 standard on characteristic limits in radiation measurements, but with important modifications suited to applying that standard to Non-Destructive Assay (NDA) applications. The ISO 11929 standard has been widely adopted, but the MDA calculation it specifies is best suited for measurements in laboratory environments where conditions are well controlled and uncertainties can be kept small; when measurement uncertainties become large and can violate the assumptions of the Gaussian error model upon which the calculation relies, it has been shown to yield inaccurate or non-physical results. Because large measurement uncertainties are often unavoidable in NDA applications, a hybrid calculation that applies log-normal error distributions for all uncertainty components other than counting statistics was implemented in NDA 2000. This hybrid approach has been found to consistently produce physically meaningful MDA estimates even for very large values of the relative uncertainty, while reproducing the results of the ISO 11929 and Currie detection limits for intermediate and small values of the relative uncertainty.