Reference, Questions and Help > Instrument Q&A

MDA vs. MDC

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Bear3705:
What is the rational for using minimum detectable concentration over minimum detectable activity for portable friskers?

Rennhack:
A frisker should be expressed as Lc (Critical detection level: the response level at which the detector output can be considered "above background", in net CPM), or MDCR (Minimum detectable count rate).
Neither of those items take into account detector efficiency, or unit conversions.  It is a 'pure' measure of an instruments ability to make that clicking sound with consistency. Independent of WHAT it is looking at.

MDA (Minimum detectable activity) adds those efficiencies.  But you would need to know the detector efficiency for your specific radionuclide(s) of interest.


Then there is LLD (Lower limit of detection), which factors in mass unit, area or volume.
or LD (Minimum significant activity level, i.e., the activity level that can be seen with a detector with a fixed level of certainty)

I guess I CAN remember things from 20 years ago.

GLW:

--- Quote from: Rennhack on Jun 01, 2021, 05:48 ---A frisker should be expressed as Lc (Critical detection level: the response level at which the detector output can be considered "above background", in net CPM), or MDCR (Minimum detectable count rate).
Neither of those items take into account detector efficiency, or unit conversions.  It is a 'pure' measure of an instruments ability to make that clicking sound with consistency. Independent of WHAT it is looking at.

MDA (Minimum detectable activity) adds those efficiencies.  But you would need to know the detector efficiency for your specific radionuclide(s) of interest.


Then there is LLD (Lower limit of detection), which factors in mass unit, area or volume.
or LD (Minimum significant activity level, i.e., the activity level that can be seen with a detector with a fixed level of certainty)

I guess I CAN remember things from 20 years ago.

--- End quote ---

peteshonkwiler:
A frisker will detect alpha, beta, and gamma radiation.
MDC is more applicable for the different radiations and mix of nuclides present while MDA is more applicable when the isotopes are narrowed to those known to be present and/or for which the instrument is source checked.

Bear3705:
Thank you both. That makes more sense to me. It was eating me alive.

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