Re: Lead shielding installation techniques

[Douglas Simpkin <dsimpkin@execpc.com>]

I am forwarding to the list Joel Gray's response to the question of lead
caps over screws through lead shielding for diagnostic x-ray installations.

Joel writes:
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If steel screws are used there is no need for concern about reduced
attenuation.  The steel that replaces the lead (which is not removed but
pushed aside) more than compensates for the attenuation of lead that is
displaced at diagnostic energies at least up to 1.5 mm of lead, and
probably for thicker lead.

I base this conclusion on radiographs made of screws in lead and of
transmission measurements.  At 120 kVp the transmission in the area around
(and including) a screw is actually decreased slightly compared to the
transmission in lead alone.

Bear in mind that the lead is being attached (usually) to steel studs so in
addition to the steel screw you have at least two thickness of the steel in
the stud.  However, my comments above do not take the additional steel from
the studs into accound.

In my opinion, there is no need use lead caps on screws nor to provide
additional lead in any way around the screws in lead shielding in
diagnostic x-ray rooms.  (I cannot comment on aluminim screws as I have not
made radiographs or measurements.  However, I would suspect that these are
seldom used as they would have difficulty penetrating steel studs and would
strip easily.)

If there are any comments or replies I would appreciate if you could copy
me on them as I am not a RADSAFE subscriber.

          Joel

Joel E. Gray, Ph.D., Consultant
2804 Second Street Southwest, Suite 334
Rochester, Minnesota 55902

Business Phone  507-269-4247
Fax  507-286-8910
Home Phone  507-286-8910
e-mail  joelgray@sprynet.com

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Douglas J. Simpkin, Ph.D., DABR
St. Luke's Medical Center
2900 West Oklahoma Avenue
Milwaukee, WI 53215
phone: (414)649-6457
fax: (414)649-5061
email: dsimpkin@execpc.com
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