NukeWorker Forum

Reference, Questions and Help => Nuke Q&A => Instrument Q&A => Topic started by: Bear3705 on Jun 01, 2021, 10:58

Title: MDA vs. MDC
Post by: Bear3705 on Jun 01, 2021, 10:58
What is the rational for using minimum detectable concentration over minimum detectable activity for portable friskers?
Title: Re: MDA vs. MDC
Post by: 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.
Title: Re: MDA vs. MDC
Post by: GLW on Jun 02, 2021, 08:48
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.








Title: Re: MDA vs. MDC
Post by: peteshonkwiler on Jun 03, 2021, 08:05
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.

Title: Re: MDA vs. MDC
Post by: Bear3705 on Jun 14, 2021, 06:36
Thank you both. That makes more sense to me. It was eating me alive.
Title: Re: MDA vs. MDC
Post by: Rennhack on Jun 16, 2021, 09:44
Self consumption can be a slippery slope indeed. For an additional apertif, consider the fact that MDC is apriori and confident at a level of 0.95. Could come in handy in China. Raising local population dose limits will not affect the statistical variation(statistics) of counting instrumentation. ALARA applies to all humans, regardless if they have been trained or not.

 WTF