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RE: Medical waste held for decay -Clarification
Joelle
The first question: For NRC Licensee's of broadscope, it is in the
License "..appropriate instrument...most sensitive scale...no
shielding...low-background area...cannot be distinguished from
background."
The second question: LSC may be an appropriate instrument (for liquid
samples), LSC can vary in background due to the fluor used, window
settings, age (refrigerated or ambient). Nevertheless, you can
statistically determine that your decayed sample is not more than 2
sigma of the average background for the LSC's isotope specific window.
The value of the final survey is demonstrated when your survey reveals
that there is "other stuff" that was not accounted for in the waste, the
original estimate of starting activity is 5 times too-low, etc., etc.
Mike Drzyzga
RSO
Hoffmann-La Roche
> ----------
> From: Joelle Key[SMTP:jkey@mail.state.tn.us]
> Sent: Friday, September 18, 1998 10:00 AM
> To: Multiple recipients of list
> Subject: Medical waste held for decay -Clarification
>
> I appreciate everyones answers.... I would appreciate your indulgence
> for a little more information.
>
> I still have two parts of my question which I think are being answered
> but
> I want to be really clear.
>
> 1) In eference to the final surveylevel, I have heard
> "indistinguishable
> from background," "twice background" and "essentially nothing left."
>
> That is really my question. Is twice background generally accepted?
> A
> few answers have implied that this isn't enough. But as we all know
> in
> radiation there really isn't a zero.
>
> 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. Someone
> mentioned using an LSC to count for this isotope. I haven't used
> liquid
> scintillation outside of training courses, so my question here may be
> really dumb. The comment sounds as if any counts in LSC are
> significant. Does LSC not have a background rate? Are we still
> looking
> at twice background here or can we look for zero? What do people
> ususally do in this case?
>
> Thanks again for all your answers. I have included the original
> question
> below if you missed it.
>
> **********Original Question************
> When a medical or research facility holds short-lived nuclides for 10
> half-lives to decay, how much can still be left and still consider the
> material "gone." I would think that it should be completely gone to
> be
> gone but isn't this impracticle? Is this nuclide specific?
>
>
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