Effects of radiation damage on thermoluminescence spectra and crystal structure of natural sphene and epidote

The spectral composition of the visible thermoluminescence (TL) glow emitted by various natural crystals of sphene and epidote has been studied. All naturally damaged samples were found to exhibit a reduced contribution in the spectral component lying in the blue-green region relative to that from undamaged ones. When the degree of damage was varied by means of annealing the samples at various temperatures, the ratio R of emission at 455 nm to that at 570 nm, in the case of sphene increased linearly with annealing temperature; i.e. as the damage was healed, the TL emission shifted towards the blue. For comparison, the effect of artificially induced damage was investigated. Again, R was found to decrease with increasing damage. An X-ray diffraction study of naturally damaged sphene showed an increase in the unit cell dimensions of the crystal with increasing damage. When damaged samples were annealed a significant decrease in cell dimensions at temperatures between 200 and 6000C was observed. In the case of epidote, the most significant change in the crystal structure as a function of annealing temperature appears to occur in the angle β and the unit cell dimension a. (author)