Re: LiF-Teflon Dosimeters

["Lindsay Tremethick" <lindsay@gh.vic.gov.au>]

> 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