RE: Portable Lead Shields

["Carroll,Raymond" <carrollrg@pgdp.usec.com>]

"Cold flow" has occurred in lead.  The instances I heard of were for lead
sheets attached to or bonded to plywood or some other support structure.  I
am not familiar with the shields you are asking about.  I havw heard that
using a Pb alloy, such as discussed in Chris' reply, minimizes or prevents
the "cold flow".  All this to say it is a valid question.  The manufacturer
of the shield, if they are still in business, should be able to help answer
the question.

Ray Carroll
carrollrg@pgdp.usec.com
______________________________________________________________

-----Original Message-----
From: Chris Alston [mailto:alstonc@odrge.odr.georgetown.edu]
Sent: Friday, December 03, 1999 7:57 AM
To: Multiple recipients of list
Subject: Re: Portable Lead Shields


David

I've never seen a "running" effect, even in shields that were decades old.
Bear in mind that it's not pure Pb, but an alloy, and usually is held in a
steel supporting frame. However, it's a perfectly legitimate question (from
a JCAHO surveyor, "mock" or not). To those of you outside the medical
field, please note that these shields typically provide at least a
tenth-value layer for Cs-137.

The answer(s) should be: that the integrity of the shield is verified, by
measurement of the transmitted radiation, with a calibrated instrument,
every time it is used. If one takes a reading just above the edge of the
shield, and one just below it, at the locus of highest exposure rate, this
is easy to do.

Good luck with the real thing
chris a.

At 04:17 PM 12/2/99 -0500, you wrote:
>I have a question in reference to the lead shields that we use to place in
>front of beds for the in-house implant patients.  These are the ones that
>roll and are very heavy.  Does the lead in these shields "settle" or "run"
>to the bottom such that the ability to reduce beam intensity is less at the
>top than at the bottom?  If so, do we x-ray these the way we do aprons?
>And then do we dispose of them and replace them?  How often?
>
>
>PS:  this was asked by a mock JCAHO surveyor
>
>thanks, david
>
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