Re: Extremity Doses and Iodine

[Bob Flood <bflood@SLAC.Stanford.EDU>]

I recommend that you talk to your TLD processor about chemical
contamination possibilities. Li phosphors are sensitive to hydrogen sulfide
and other compounds, and especially to sulfur bearing ones. If the
processor captures glow curves, obtain a printout and satisfy yourself that
the glow curve looks like radiation. A chemical effect will usually not
exhibit the usual glow peak shape (it looks like noise).

On the subject of radioactive contamination, do you ever see particles of
I-125 in your facility? A particle lodged on the dosimeter could deliver a
very high localized dose, and the particle itself could be lost easily in
shipping, receiving, disassembly, etc.

The only experience I can relate that remotely applies has to do with whole
body dosimeters. Two dosimeters indicated an unexpected skin dose, with no
lens or deep dose at all. Given the mix of isotopes on the site, there was
no credible scenario for receiving a significant skin dose in the absence
of lens and deep dose. Investigation found that both wearers worked the
"grease truck," a mobile oil changing operation that moved about the site
(U-mill decommissioning) doing routine oil changes and greasing of the
heavy machinery. It seems that either 1) the moly sulfide greases they
routinely used may have affected the least protected element of the
dosimeter (resulting in an apparent shallow dose) or 2) an oil film over
the first element could have trapped a thin layer of mill tailings over the
element, resulting in a dose to the phosphor. However, in this case, the
shallow doses were about 200 mrem, which means the contamination scenario
can realistically result in such a dose (much more difficult when
discussing 70 rem). Having glow curves recorded would have been a major
help, but...


Bob Flood
Stanford Linear Accelerator Center
(415) 926-3793     bflood@slac.stanford.edu
Unless otherwise noted, all opinions are mine alone.