Bleaching and phototransfer of thermoluminescence in limestone

The thermoluminescence from a French limestone shows peaks in the glow curv e at 142 +/- 11, 164 +/- 14, 194 +/- 11, 286 +/- 10 and 360 +/- 10 degrees C measured at a heating rate of 5.2 degrees C s(-1). The bleaching and phot otransfer properties of these peaks are presented for bleaching times in a solar simulator extending up to 2 weeks. The height of the principal peak i n the glow curve at 286 degrees C declines exponentially with bleaching tim e over the first 10 min and then over the following 2 weeks declines in pro portion to t(-0.34+/-(0.01)), where t is the bleaching time. The peak at 36 0 degrees C is bleached exponentially with time over a period of 60 min and thereafter shows no detectable change in intensity. The phototransferred t hermoluminescence rises to a maximum at 4 min of exposure in the solar simu lator and thereafter for 2 weeks falls proportionally to t(-0.32+/-(0.02)), where t is the exposure time. The wavelength dependence of the bleaching o f the principal 286 degrees C peak in the natural thermoluminescence glow c urve was investigated over the wavelength range 340-750 nm, obtained using optical filters and the solar simulator. The 340-400 nm region was found to be of most importance for bleaching, while wavelengths longer than 500 nm had little influence. (C) 1999 Elsevier Science Ltd. All rights reserved.