Answer to Question #688 Submitted to "Ask the Experts"

Q

I have started working with TLD GR200A (Chinese) for radiotherapy doses. After six cycles(following manufacturer's instructions), average readout of 100 dosimeters has decreased three percent in a nonlinear way. Is it normal for GR200A? How can I use an individual factor?

A

The phosphor GR200, a different version of the original Lif:Mg,Ti phosphor, was developed in China and uses Mg, Cu, and P as dopants. The dosimeter has the advantage of greater sensitivity than the traditional LiF and a lack of supralinearity. It has been used successfully in many applications, including personal dosimetry, environmental dosimetry, and medical therapy dosimetry. One of the problems at the higher doses used in some medical applications has been a higher residual dose that can lead to elevated response with multiple uses. There has been work done that has shown response changes depending on the time interval between exposure and readout, but these changes have also generally been in the positive direction. I have not heard of a decrease in response as being typical for these dosimeters, although this might be possible depending on the particular anneal cycle that is being used. There are many articles in the technical literature on the evaluation and use of LiF:Mg,Cu,P. One reference with many articles on this phosphor that might be appropriate is Radiation Protection Dosimetry 85(1-4): 1999. George Chabot, CHP