Re: Roof shielding calc

[Dave Derenzo <dave@uic.edu>]

Robert,

If you do it the way your colleague indicates, the roof may need to become 
a restricted area.  This will involve posting warning signs and/or warning 
indicators, security to prevent inadvertent access, control of when and who 
is on the roof, and training of those most likely to be on the roof.  You 
will also want to do a complete survey of the facility at 15 MeV to 
determine the radiation levels outside the building and calculate the 
maximum credible dose to members of the public and to workers.

There are others on this list who can help you with skyshine calculations.

Dave Derenzo

At 05:41 PM 8/28/00 -0500, you wrote:
> >From: Robert Shaltoni <rshaltoni@HOTMAIL.COM>
> >
> >List members;
> >
> >I have a question about roof shielding.   We have a 6MV Linac that we will
> >upgrade to 15MV.  The roof has 3 feet of concrete and according to my calcs,
> >we need an additional 46 inches of concrete.  It is a free standing clinic
> >and there is nothing on the roof.  These are the factors that I used:
> >
> >W= 50,000
> >U= 0.25
> >T= 1/8  even though no one goes up  on the roof at all.
> >d= 7 feet from isocenter to ceiling, and 3 feet existing concrete
> >Uncontrolled access
> >
> >My senior colleague, says that we do not need any extra shielding on the
> >roof because it is not occupied!! is that true, what about skyshine?  He
> >says 3 feet is enough?
> >
> >I appreciate your help.
> >
> >Regards,
> >
> >Bob
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Dave Derenzo, MPH  (dave@uic.edu)
Associate Director for Radiation Safety
Radiation Safety Officer
University of Illinois at Chicago
Radiation Safety Section, MC932
820 S. Wood St., Chicago, IL 60612-7314
Voice:(312)996-7429  Fax:(312)996-8776
URL:  http://www.uic.edu/depts/envh

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