[ RadSafe ] TLD Glow curves

[Neill Stanford]

Since Sandy seems to be worn out from the background question...

Fade: LiF has not only post-irradiation loss of signal or fading, but
interestingly enough also pre-irradiation loss or sensitivity. If you store
a LiF dosimeter that has been annealed for use, the longer you store it
before irradiating it, the less signal you will ultimately measure. This is
now a well known phenomenon and can be minimized with a special anneal
treatment (not machine anneal) or estimated and corrected for arithmetically
after the fact. I can attest that in the mid-1980's this was not so
well-known, even by the manufacturer of LiF.

But the original question was about glow curves. Most TLD processors use
glow curves as an analysis tool for verifying proper readout of a suspicious
result. Glow curves can be used to show non-Tl light indicating burn-off of
some foreign material; incomplete readout (especially valuable for older
contact-heating readers); and even radioactive contamination. Some users
have experimented with 100% glow curve analysis. Back in 1984 I did this
with Harshaw 2271 readers to check for incomplete readout of the chips
caused by poor contact with the heating element. 

Neill Stanford, CHP
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-----------------------------------

Back in 1985, a colleague of mine did a study and literature search. He
published an in-house article on LiF TLD Fading. His study concluded that
with time, irradiated TLDs can expect some fading. Also those that are store
for a specific period of time at ambient temperatures and not irradiated,
can expect fading or 'loss of signal'.

Ed

Edmond J. Baratta

Radiation Safety Officer

Tel. No. 781-729-5700, ext 728

FAX: 781-729-3593

 

-----Original Message-----

From: radsafe-bounces at radlab.nl [ <mailto:radsafe-bounces at radlab.nl>
mailto:radsafe-bounces at radlab.nl] On Behalf Of Falo, Gerald A Dr KADIX

Sent: Thursday, August 25, 2005 8:17 AM

To: radsafe at radlab.nl

Subject: [ RadSafe ] TLD Glow Curve Question

Hi all,

These discussions about background subtraction concerning TLDs and so on got
me wondering about other spurious readings on TLDs. Do current TLD readers
analyzed the glow curve itself to detect anomalies that would indicate and
non-radiation related result? I recall some work from the mid-1980s that
showed glow curves from impacts, sweat, soap, etc., but I don't recall if
glow curve anomalies were used to discriminate against spurious readings.

Thanks,

Jerry

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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