Elimination of the Residual Signal in LiF:Cu,Mg,P

Abstract

The relative intensity of the residual signal (ratio of the second readout to first readout) is an important parameter in the application of 'unannealed' TL materials in personnel and environmental dosimetry. Previous studies have indicated a significant residual in LiF:Cu,Mg,P (GR-200, Beijing); 2-3% following 240 oC for 10 s readout and 3% following even 270 oC readout. These residual signals arise from a high temperature peak at approximately 270 oC in GR-200 with an intensity of approximately 7-25% relative to the main dosimetry peak. We have continued our multiparameter investigation of the LiF:Cu,Mg,P preparation technique with a view to minimising the residual signal. Conventional preparation techniques lead to a material with a TL sensitivity 35±4 (1 SD) greater than that of LiF:Mg,Ti(TLD-100, Harshaw), with a residual signal of 4-5% following 240 oC for 10s readout. Incorporation of oxygen in the melt suppresses the high temperature TL and leads to a residual signal of 2-3% with no loss of sensitivity in the main dosimetric peak. It is also possible to prepare a material (SSD-NR) with a sensitivity 17±2 (1 SD) times greater than that of TLD-100 but with a residual signal of only 0.25-0.5% following 240 oC for 10 s readout. This negligible residual is achieved via almost total elimination of the high temperature peak and renders the material usable in unannealed form. The chemical configuration of the incorporated phosphorous has an important influence on both the TL sensitivity and the residual signal. The number of OH groups attached to the phosphorus atom seems also to have a direct influence on the main peak sensitivity indicating that these ions play a role in the TL mechanism.