RE: Portable Lead Shields

[Matthew Schmid <mschmid@scf.sk.ca>]

Radsafers:

The lead shields we have are basically a steel frame filled with very fine
lead shot (I would estimate the average diameter at about 0.5 mm). Although
ours are very old, I have seen the same ones advertised for sale in current
catalogues. I suspect that most of the lead shields out there are a similar
design.

Our shields have a filling cap on top. I removed it once to look inside. The
level of the top of the lead shot was about one inch down from the top of
the shield. Since these shields were here long before I was, I am not sure
if they changed over time or if they were always like this. Either way, it
is a good idea to check your shields to see where the "effective" top of the
shield is.

Matt





At 08:29 AM 12/03/1999 -0600, you wrote:
>"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
>>

Matthew Schmid, M.Sc., MCCPM
Allan Blair Cancer Centre
Regina, Sask., Canada S4T 7T1
(306)766-2319     FAX (306)766-2845
mschmid@scf.sk.ca

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