Re: LiF-Teflon Dosimeters

["GammaMan" <gammaman@msn.com>]

 You want to contact Teledyne Brown Engineering (Once Teledyne Isotopes).
They manufacture a variety of TLD / Teflon based devices.  The number is
201-664-7070.  They are located in Westwood NJ.  Ask for Bruce Terry.  I
once ran their TLD/Nuclear Instruments Department in the early 80's.  We
once manufactured LiF and CaSO4:DY in many different teflon configurations
(discs, rods, ultra thins, Radiguard Dosimeters).  By the way, heating PTFE
(Polytetrafluoroethelyene) more commonly known as teflon to 400C will
vaporize it.  The vapor caused by the breakdown of PTFE will cause "Teflon
Flu".  The individual, if exposed to enough of the vapor, will think he/she
has the worst case of the flu.

Lithium based TLD's require very precise annealing cycles at various
temperatures.  We once had many technical documents which described the
handling and annealing of these types of dosimeters.  I don't know if these
documents still exist or have been updated.    The information I remember is
as follows:

For LiF-7:  Anneal at 300C for 1.5 hours,  Reduce the temperature to 80C and
anneal for an additional 14 hours.
For LiF-6/CaSO4  Anneal at 260C for two hours.

Effects of LiF7 to UV light is also well documented.  Bruce should be able
to guide you in the proper direction.

Good Luck.

-----Original Message-----
From: Lindsay Tremethick <lindsay@gh.vic.gov.au>
To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
Date: Sunday, September 07, 1997 8:16 PM
Subject: Re: LiF-Teflon Dosimeters



>> I would like to solicit some specific information about LiF-Teflon disc
>> dosimeters.
>> 1. I need to better understand how UV light (from flourescent fixtures)
can
>> affect the phosphor. I would be especially interested in any published
data
>> (i.e., looking for references).
>
>Can't help here but I maintain TLD's in a dark enviroment till use. I
>have never looked into any UV light effects but the Victoreen manual
>said it happened!
>
>> 2. Annealing practices: I'd like to know what annealing cycles are used,
>> including temperature and time combinations, whether ovens are preheated
>> with dosimeters placed into a hot oven or the dosimeters are placed into
a
>> cold oven and then heated, etc.
>
>The teflon DOES NOT like high temps. I managed to ?damage? a few
>teflon rods in the early days before I have read the instructions!!!!
>The rods now have a somewhat unpredictable response, if there is any
>predicability in teflon based TLD!!!
>
>The standard quick TLD anneal cycle of 400 C for an hour and 100 C
>for two hours is simply too hot. Unfortunately using a 300 C cycle
>does not fully clear all traps in the LiF, hence there is some signal
>left and I don't have any other choices other than the pre-programmed
>temps. I think a better temp is about 350 C but I am sure if that is
>incorrect someone else will put it straight. My oven usually starts
>from room temp or close too depending on how quickly things have to
>be done. Waiting for an over to cool down is about as exciting as
>watching paint dry! The TLD's all sit on stainless steel trays which
>very quickly attain room temp so it is only the oven internal
>enviromental temp that might be higher maybe 30-35 C.
>
>I have only ever had a dose response reproducibility of about 5-7%
>with the teflon disks but they are easier to work with than the small
>solid LiF chips. To keep track of them you can mark them with a
>graphite pencil without any problem, then it is really easy to sort
>them out when you drop the holding container on the floor!!!!!!!!!!
>
>If ther is anything else contact me otherwise
>Good luck
>All the standard disclaimers!!
>Lindsay Tremethick
>Radiation Oncology
>Geelong Hospital
>Geelong, Victoria, Australia
>Lindsay@gh.vic.gov.au
>
>