Minimum detectable activity

Minimum detectable activity (MDA) is the lowest activity of a radioactive nuclide that can be detected with a detector, to some confidence level.^[1]^{[page needed]} It is a concept that is used in several circumstances, such as in whole-body counting or radiation monitoring, to aid in determining the presence or absence of a radioactive substance or comparing the performance of different detector systems. There are several ways to calculate MDA that are commonly used, including the ISO11929 standard and the Currie method.^[2] The Currie method is given by^[3]

$MDA={\frac {L_{D}}{\epsilon \cdot P\cdot t}}$ ,

where $L_{D}$ ins the detection limit in units of counts, $\epsilon$ is the detection efficiency of the detector, $P$ is the emission probability of the radiation, and $t$ is the live time of the measurement. The formula for $L_{D}$ will vary depending on the specified confidence level. For false-negative and false-positive rates of 5%,^[1]

$L_{D}=2.71+4.65{\sqrt {B}}$ ,

where $B$ is the background counts. In other words, to achieve a low MDA, low background counts and a high efficiency are desired. Methods to decrease MDAs include utilizing coincidence measurements,^[4] large detection volumes,^[5] or using large shielding and underground measurement facilities.^[6]

References

^ ^a ^b Gilmore, Gordon (2011). Practical gamma-ray spectrometry (2., repr. with corr ed.). Chichester: Wiley. ISBN 978-0-470-86196-7.
^ Done, L.; Ioan, M-R. (2016). "Minimum Detectable Activity in gamma spectrometry and its use in low level activity measurements". Applied Radiation and Isotopes. 114: 28–32. Bibcode:2016AppRI.114...28D. doi:10.1016/j.apradiso.2016.05.004. ISSN 0969-8043. PMID 27172893.
^ Currie, L. A. (1968). "Limits for qualitative detection and quantitative determination: Application to radiochemistry". Analytical Chemistry. 40 (3): 586–593. Bibcode:1968AnaCh..40..586C. doi:10.1021/ac60259a007. ISSN 0003-2700.
^ Britton, R.; Davies, A. V.; Burnett, J. L.; Jackson, M. J. (2015). "A high-efficiency HPGe coincidence system for environmental analysis". Journal of Environmental Radioactivity. 146: 1–5. Bibcode:2015JEnvR.146....1B. doi:10.1016/j.jenvrad.2015.03.033. ISSN 0265-931X. PMID 25875083.
^ Keyser, R. M.; Twomey, T. R.; Wagner, S. E. (1990). "The Benefits of Using Super-Large Germanium Gamma- Ray Detectors for the Quantitative Determination of Environmental Radionuclides" (PDF). Ortec. Retrieved 10 November 2025.
^ Laubenstein, M.; Hult, M.; Gasparro, J.; Arnold, D.; Naumaier, S.; Heusser, G.; Köhler, M.; Povinec, P.; Reyss, J.-L.; Schwaiger, M.; Theodórsson, P. (2004). "Underground measurements of radioactivity". Applied Radiation and Isotopes. 61 (2–3): 167–172. Bibcode:2004AppRI..61..167L. doi:10.1016/j.apradiso.2004.03.039. ISSN 0969-8043. PMID 15177339.

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[gilmore-1] Gilmore, Gordon (2011). Practical gamma-ray spectrometry (2., repr. with corr ed.). Chichester: Wiley. ISBN 978-0-470-86196-7.

[2] Done, L.; Ioan, M-R. (2016). "Minimum Detectable Activity in gamma spectrometry and its use in low level activity measurements". Applied Radiation and Isotopes. 114: 28–32. Bibcode:2016AppRI.114...28D. doi:10.1016/j.apradiso.2016.05.004. ISSN 0969-8043. PMID 27172893.

[currie-3] Currie, L. A. (1968). "Limits for qualitative detection and quantitative determination: Application to radiochemistry". Analytical Chemistry. 40 (3): 586–593. Bibcode:1968AnaCh..40..586C. doi:10.1021/ac60259a007. ISSN 0003-2700.

[4] Britton, R.; Davies, A. V.; Burnett, J. L.; Jackson, M. J. (2015). "A high-efficiency HPGe coincidence system for environmental analysis". Journal of Environmental Radioactivity. 146: 1–5. Bibcode:2015JEnvR.146....1B. doi:10.1016/j.jenvrad.2015.03.033. ISSN 0265-931X. PMID 25875083.

[5] Keyser, R. M.; Twomey, T. R.; Wagner, S. E. (1990). "The Benefits of Using Super-Large Germanium Gamma- Ray Detectors for the Quantitative Determination of Environmental Radionuclides" (PDF). Ortec. Retrieved 10 November 2025.

[6] Laubenstein, M.; Hult, M.; Gasparro, J.; Arnold, D.; Naumaier, S.; Heusser, G.; Köhler, M.; Povinec, P.; Reyss, J.-L.; Schwaiger, M.; Theodórsson, P. (2004). "Underground measurements of radioactivity". Applied Radiation and Isotopes. 61 (2–3): 167–172. Bibcode:2004AppRI..61..167L. doi:10.1016/j.apradiso.2004.03.039. ISSN 0969-8043. PMID 15177339.

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