Re: LNT and resources [Was: Scientific responsibility]

[John Jacobus <crispy_bird@YAHOO.COM>]

Gary,

Shielding is certainly reasonable problem for a small

scale operation.  At our place, I did a shielding

evaluation of a new C-Arm, and recommended only 1/32"

lead of one wall.  The comment was, "Well, we can

order and use 1/16" all around."  The difference in

price was too small to worry about.  



By the way, I assume you were not taking "credit" for

the concrete slab between the floors.



--- Gary Isenhower <garyi@trinityphysics.com> wrote:

> 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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=====

-- John

John Jacobus, MS

Certified Health Physicist

e-mail:  crispy_bird@yahoo.com



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