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RE: MDA vs. Critical level for DOE Free Release surveys

Also suggested reading - Mayer and Dauer, HPS Vol. 65, No 1, pp 89-91,

1993.



-----Original Message-----

From: owner-radsafe@list.Vanderbilt.Edu

[mailto:owner-radsafe@list.Vanderbilt.Edu] On Behalf Of William V Lipton

Sent: Tuesday, October 28, 2003 3:09 PM

To: Goff, Tom

Cc: ''RadSafe Send Message'

Subject: Re: MDA vs. Critical level for DOE Free Release surveys





You have to use both concepts.  Briefly:



The critical level is an after the fact decision point: Is the count due

to radioactive contamination or is it variation in background, i.e., can

the material be free released?  This is usually set to provide for 5%

"Type 1" error; i.e. there's a 5% chance of a false positive.



The MDA is an a priori evaluation of your assay system.  It is set so

that, for a sample which contains an MDA of contamination, the actual

count will exceed the critical level with 95% confidence, i.e., a 5%

"Type 2" (false negative) error.



I believe that Glenn Knowles's book has a good explanation of this.



The opinions expressed are strictly mine.

It's not about dose, it's about trust.

Curies forever.



Bill Lipton

liptonw@dteenergy.com





"Goff, Tom" wrote:



> >       Title:

> >

> >       We are discussing using a critical level for free release 

> > surveys. Please provide answers to the following:

> >

> >       Are you using critical value or MDA for free release surveys 

> > of materials from your site?

> >

> >       Does anyone have a reference/regulatory standard on whether to



> > use MDA or critical value for free release surveys?

> >

> >       Given that an MDA results in a 95% confidence in detecting 

> > contamination at the MDA value, what is the corresponding confidence



> > if using the critical level?

> >

> >       I would welcome any other comments or thoughts on this.

> >

> >       Tom Goff

> >

> > --------------------------------------------------------------------

> > ------

> > ----------------------------------------------------------------

> >       Let me know if you're ok with this.

> >

> >

> >

> >       Tom Goff

> >       WIPP ALARA Coordinator

> >       WIPP Integrated Waste Operations

> >       (505) 234-8861

> >       (fax)  234-8963

> >       e-mail  Tom.Goff@WIPP.ws

> >       page (505) 234-8850  (pager 479)

> >       P.O. Box 2078

> >       Carlsbad, NM 88221

> >       Radiological Engineering: Anticipating Problems.....providing 

> > solutions!!!

> >

>

> **********************************************************************

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