Analysis of nonlinear TL effects of CaF2:Dy

Calcium fluoride doped with dysprosium, very often referred to under the label TLD-200, is an important TL(thermoluminescent) dosimetric material. The broad glow curve of this material comprises four major peak structures at around 125, 150, 210 and 270 degC, besides low intensity high temperature peak structures at around 350 and 420 degC. These peaks grow at different rates with gamma dose along with conspicuous shift of glow curve maximum from peak to peak. While the TL signal integrated over a 90-300 degC temperature range shows a supralinearity factor of about 2.8, it is very difficult to precisely monitor the TL response behaviour of any individual peak. In view of this, nonlinear behaviour of different regions of glow curve of CaF2:Dy, in 1.2 - 2.0 eV range corresponding to 90 - 300 degC region, has been investigated with respect to their mean glow temperature and mean activation energy. From such a study it is observed that the high temperature/activation energy regions show considerably increased factor of supralinearity and decreased range of linearity of TL response, while lower temperature/activation energy regions show significantly extended range of linear response and a reduced factor supralinearity. The present study attempts to explain the mechanism of nonlinear TL behaviour of CaF2:Dy. (author). 9 refs., 1 tab., 1 fig