Lesson plan
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. 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. The Currie method is given by MDA = \frac{L_D}{\epsilon \cdot P \cdot t} , where L_D is 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%, 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. This is usually referred to as the Currie detection limit. Methods to decrease MDAs include utilizing coincidence measurements, large detection volumes, or using large shielding and underground measurement facilities.
Article summary
Minimum detectable activity (MDA) is the lowest activity of a radioactive nuclide that can be detected with a detector, to some confidence level. 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. The Currie method is given by MDA = \frac{L_D}{\epsilon \cdot P \cdot t} , where L_D is 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%, 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. This is usually referred to as the Currie detection limit. Methods to decrease MDAs include utilizing coincidence measurements, large detection volumes, or using large shielding and underground measurement facilities.
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
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Key claims and bibliography are generated from the same tracked claims and sources as the article page.