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RE: Exposure from flight
Hi Rob.
I used standard laboratory procedures to read the chips. I do environmental
TLD reading for our facility, and used the calibration curves for last
quarter to evaluate the readings for the twelve chips I carried with me. Six
were in my luggage and the others were on my person. I did NOT do a
backround, so the readings were gross mR, not net mR. The linear regression
curve used to calculate gross mR per nanocoulomb was based on calibration
TLD's exposed to a NIST-traceable Ra-226 needle source. All initial and
final light and dark currents were congruent with those taken last time I
did the entire environmental suite.
I guess my point is that I got very little (if any) dose. If I had compiled
a set of backround TLD's and kept them in our lead "cave", I would have been
a little more accurate. But I didn't, so I'm not. My supposition is that
since the TLD's I carried on my person (and which went through several X-Ray
machines) read almost exactly the same as the ones in my luggage, most of
the dose was due to backround. I do believe however, that I received a few
mR.
Regards,
Jim
-----Original Message-----
From: Rob Gunter [mailto:rgunter@sec-tn.com]
Sent: Tuesday, May 21, 2002 4:59 AM
To: Jim Darrough
Subject: RE: Exposure from flight
Jim,
I think it is a bit more complicated than that. When you read the TLD,
there must have been some sort of background subtraction. You should check
that out to make sure the number was realistic for the time interval. After
all, the 12 mr is the result of the raw reading with a background
subtraction. The question is, what is a real number for background? Is the
lab background the same as in DC? What was the anneal history of the TLDs?
You may have done this, but next time, anneal a batch of chips in the lab
before you go. Take half with you and use the annealed chips in the lab as
your backgrounds. If you have lots of chips, you will have good statistics.
Remember also, that each chip has a different mass, and element correction
factor. On a TL dosimeter this is accounted for by the calibration. With
raw chips it is harder to keep track of. Of course you could use the means
and accept a broad standard deviation, or irradiate them all and come up
with a batch calibration factor adding the sum response of all the chips.
Individual TL dosimeter are selected to respond between 0.77 and 1.4 of the
mean.
Yours,
Rob
Robert J. Gunter, CHP
-----Original Message-----
From: owner-radsafe@list.vanderbilt.edu
[mailto:owner-radsafe@list.vanderbilt.edu]On Behalf Of Jim Darrough
Sent: Monday, May 20, 2002 6:21 PM
To: radsafe
Cc: randall_f_brich@RL.GOV
Subject: Exposure from flight
Hello!
I finally read the TLD chips I had along for my trip from Eugene, OR to
Washington, D.C. and back. Results were that I received 12mR total dose, and
so did the things in my checked baggage. This included the entire time I was
at training in Virginia where various sources were used as I kept the TLD's
on my person (except of course for the ones in my suitcase).
Interesting to note is that the ones on my person went through airport
security X-ray devices four times.
Jim Darrough
Health Physicist
Oregon State University
(541) 737-7048 - Office
(541) 737-0480 - FAX
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