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Re: LNT and resources [Was: Scientific responsibility]
I can give an example of the difference LNT is making for shielding
PET imaging centers. Consider an uptake room with office space on
the floor above at a distance of 12'. Shielding in the ceiling for this
area for various dose limits gives you the following lead thicknesses:
500 mrem/yr 8 lbs/sf
100 mrem/yr 40 lbs/sf
25 mrem/yr 60 lbs/sf
These numbers ignore shielding required for the dose due to the
adjacent uptake room and the scanner itself, so this is an
underestimate. For most buildings the typical structure of the ceiling
does not do much to reduce the dose from PET sources. NCRP says
we OUGHT to be using 25 mrem/year, and that is the logical result of
assuming LNT and ALARA.
So, what is the cost? If we follow the NCRP recommendations, then
this valuable imaging modality is going to be both hard to get and
extremely expensive, because you can't put that much lead in the the
ceiling and/or walls and/or floor of a typical building. LNT will certainly
reduce the number of sites offering PET imaging and drive the cost up
where it is available.
-Gary Isenhower
Date sent: Fri, 20 Jun 2003 05:16:48 -0700 (PDT)
From: John Jacobus <crispy_bird@YAHOO.COM>
> I have a question for the group. Can anyone give a
> idea how replacement of the LNT with a different
> model, e.g., threshold at 500 mrem or 5mSv, will
> change how business will be done in radiation
> protection? What practices will change? Surveys?
> Documentation of environmental monitoring? Staff?
> What legislation and regulations will change?
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