more on film and high energy photons

["M. Woo" <melissa@zelda.ehs.uiuc.edu>]

I realize that I'm beating a dead equine here, but I thought I should
be fair and mention that I just received a call from the fine folks at
Landauer.

The upshot is that there is a 250 keV (presumably effective) threshold
for high energy photons above which it becomes difficult, if not
impossible, for the naked eye to distinguish a filter pattern.

The reason I found the technical aspects as well as the customer
service angle important is the case where a radiation safety office
might receive a "no filter pattern" result and accuse radiation workers
of tampering with dosimetry or inability to load holders correctly.  It
is important to keep in mind that irradiation outside the holder is
apparently not the only way that a filter pattern can become
undetectable under some circumstances.  However, I was told that in the
VAST majority of cases, irradiation outside the holder really is the
cause.

We had a case a few years ago where a location monitor came back with
high energy photon exposure, no filter pattern.  Our office's response
might have been less accusatory if factors other than irradiation
outside the holder had been considered.  Granted, considering the
particulars of the case, it most likely *was* a case of tampering...
:-)

--
Melissa Woo, Health Physicist                    |mailto:m-woo@uiuc.edu
University of Illinois at Urbana-Champaign       |ofc 1.217.244.7233
DEHS, MC225, 101 S. Gregory St., Urbana, IL 61801|fax 1.217.244.6594
http://www.uiuc.edu/ph/www/m-woo                 |


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