Re: Medical waste held for decay -Clarification

[George Harder <gharder@nervm.nerdc.ufl.edu>]

At 09:01 AM 9/18/1998 -0500, you wrote:
>1)  In eference to the final surveylevel, I have heard "indistinguishable
>from background,"  "twice background" and "essentially nothing left."

It all boils down to what your license allows.  With your license you may
have included procedures that outline your instruments and how to calculate
your minimum detectable activity.  Technically, a half of a half of a half
will never get rid of every last bit of a isotope.  However, you will get to
a point where you can't detect it anymore.  That is your MDA.  As many
isotopes that there are, there are almost as many ways to calculate MDA.
The simpliest (and I'm going from memory so please don't flame me) is 4.66 *
SQRT(background/read time).  You can run a background sample through your
LSC, calculate your MDA and then read your P32 sample.  If the activity is
below MDA, its not there.  That's one approach.

>2)  My second confusion has to do with isotope dependency.  What I
>was trying to get at is in doing the final survey if you are looking at a beta
>emitter like P-32 then the G-M survey is not appropriate.

I have a LSC so doing a P-32 check with a GM hasn't been necessary.  But its
energy is high enough to get a good reading with an open-window GM tube.  As
long as you have an efficiency for P-32 and factor that into your MDA
equation, I can't see that there would be a problem (unless you have a
liquid P-32).  That's my guess but I'll bow to better advice on this part of
your question.
- George Harder (gharder@perma-fix.com)
www.perma-fix.com/florida.html
Diplomacy is the art of saying 'Nice doggie!'... till you can find a rock.

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