[ RadSafe ] "Two-scatter" rule in medical x-ray protection

John Jacobus crispy_bird at yahoo.com
Sat Apr 8 20:08:00 CDT 2006

I believe that the rule for the operator not receiving
primary scatter is based on ALARA or dose reduction. 
Generally, most operator booths have only an open
doorway, so scatter radiation will contribute to the
operators dose.  That is, the operator is exposed to
shielded primary and leakage radiation, and unshielded
scatter radiation.  Every time an exposure is made,
all three types of radiation fields are present.

--- "Falo, Gerald A Dr KADIX" <Jerry.Falo at us.army.mil>

> Hi all,
> I don't do much medical health physics but many of
> my colleagues have
> and continue to do so.  Between speaking with
> colleagues and reading
> NCRP-147, I never realized that "the booth shall be
> positioned that no
> unattenuated primary or unattenuated
> single-scattered radiation will
> reach the operator's position in the booth." The
> same or similar text
> appear in NCRP 49 and other documents.
> I'm wondering why "two-scatter" rule exists. If the
> sum of the leakage
> and scatter dose is less than the limits, then why
> does the
> "two-scatter" rule exist? As far as I can reason,
> scatter radiation is
> of a lower energy an lower intensity than either the
> primary or leakage,
> so it's not a question of radiation quality. Is it
> simply an ALARA
> consideration?
> Thanks for your time and patience.
> Jerry Falo
> ________________________________
> The statements and opinions expressed herein are my
> responsibility; no
> one else (certainly not my employer) is responsible,
> but I still reserve
> the right to make mistakes.
> Don't panic! - Douglas Adams in "The Hitchhiker's
> Guide to the Galaxy"
> Gerald A. Falo, Ph.D., CHP
> Kadix Systems 
> U.S. Army Center for Health Promotion and Preventive
> Medicine - Health
> Physics Program
> jerry.falo at us.army.mil
> 410-436-4852
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"We fear things in proportion to our ignorance of them."
Titus Livius
-- John
John Jacobus, MS
Certified Health Physicist
e-mail:  crispy_bird at yahoo.com

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