Roof shielding calc

[Chris Alston <alstonc@odrge.odr.georgetown.edu>]

>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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