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Re: TLDs - False Positive Betas
- To: radsafe@romulus.ehs.uiuc.edu
- Subject: Re: TLDs - False Positive Betas
- From: Robert Jeffrey Gunter <GUNTERRJ@kohis.a1.ornl.gov>
- Date: Thu, 20 Jul 1995 08:05:00 -0400 (EDT)
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We issue about 130000 dosimeters per year and see the false positive on
occasion. We are using a 4 element tld with a 0.0036" thick element for Beta
particle detection. The other elements are 0.015". The thin chip is no longer
sold with that thickness.
A study of this problem using 10,000 cards was performed here at ORNL by Ed
Sonder and Abu Ahmed. It is called "Analysis of Anomalous Data Produced by
Harshaw Model 8801 Thermoluminescent Dosimeter Cards" ORNL/TM-12311, May 1993.
They found that 218 cards had a problem with the thin chip and only 3 cards had
a similar problem with a thick chip.
To quote the paper: "These false readings are usually accompanied by irregular
glow curve shapes. Once a chip gives bad results, its probabilityu of giving
future excess readings is elevated. Moreover, the history of the suspect
dosimeters often indicates a previous tendency towards elevvated readings for
the same chip." You can either call the ORNL library to get a copy, or me.
ORNL Library: 615 574-6744
Good luck,
Rob Gunter
ORNL
615-576-6317
Internet: gunterrj@ornl.gov