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Decision threshold associated with multiple measurements. Application to the synthesis of the environment monitoring results

  • A. Vivier (a1), G. Manificat (a2), J-L. Picolo (a3), S. Fleury (a3), M. Mokili (a4) and X. Guo (a5)...

Abstract

When the sample activity is measured for various reasons several times, then with each measurement can be associated an individual decision threshold and limit of detection. Each measurement can be analyzed through its own decision threshold. The whole measurements can sometimes present contradictory results, some measurements being lower than the decision threshold and other higher. The problem then arises to build a decision threshold and a detection limit taking into account all the individual results, and to decide if the radioactivity is finally detected or not. It is interesting to note that it is possible sometimes that the decision threshold taking account all results makes it possible to decide that the radioactivity is present whereas the totality of the individual results are negative in terms of individual decision threshold. The purpose of this article is to show how these thresholds and these coherent limits cumulated can be determined in way according to the experimental conditions. In a general way a rigorous method of cumulating makes it possible to systematically decrease the decision threshold and limit of detection in terms of activity. This approach has interesting applications in gamma spectrometry with multi-emitters, discharge or periodical environmental measurements. On the basis of measurements realized by the IRSN within the framework of the national monitoring of the environment, we will see the potential impact of these methods on the final assessments.

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References

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[1]AMC (2001) What should be done with results below the detection limit? Mentioning the unmentionable. Analytical methods committee technical brief No. 5, April 2001. Royal Society of Chemistry, London, 2001, two unnumbered pages.
[2]ISO 11929 (2009) Determination of the characteristic limits (decision threshold, detection limit and limit of the confidence interval) for measurements of ionizing radiations.
[3] Fiévet, B., Della Vedova, C. (2010) Dealing with non-detect values in time-series measurements of radionuclide concentration in the marine environment, J. Environ. Radioact. 101 (1), 1-7.
[4]Helsel D.R. (2005) Nondetects and Data Analysis: Statistics for Censored Environmental Data. John Wiley and Sons, New York, p. 250.
[5]MARLAP, Multi-Agency radiological laboratory Analytical protocols manual (2004) Vol. III EPA 402-B-04-001C, chapter 20, US Environmental Protection Agency
[6]Vivier, A., Aupiais, J. (2007) Optimization of the decision threshold for single radioactive counting, J. Radiochim. Acta 95, 477-492.
[7]Vivier, A., Fottorino, R., Rousse, B. (2010) Seuil de décision et limite de détection : estimation interprétation et optimisation, 1ère partie : principes de bases, Radioprotection 45, 321-343.

Keywords

Decision threshold associated with multiple measurements. Application to the synthesis of the environment monitoring results

  • A. Vivier (a1), G. Manificat (a2), J-L. Picolo (a3), S. Fleury (a3), M. Mokili (a4) and X. Guo (a5)...

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