EPR and ENDOR investigations on the X-ray storage phosphors BaSO4 and SrSO4

X-ray storage phosphors are applied in many areas including medical diagnostics, crystallography or material inspection. The main advantage of this method compared to conventional X-ray films is the linearity of dose response over more than six orders of magnitude. The readout procedure by scanning with a laser, however, implies severe restrictions with respect to the decay time of the photostimulated luminescence. Therefore a need for fast phosphors exists. We found that BaSO4 and SrSO4 decay in the 10 ns range and therefore are very promising materials. Investigation of the thermally stimulated luminescence of these compounds after X-irradiation at room temperature and parallel of the photostimulability showed that a lot of X-ray energy is stored in centers not effective for the latter process. We therefore thoroughly investigated by EPR and ENDOR the radiation effects in the two sulfates and their thermal stability. Phosphate and F+-centers turned out to play an important role for this application. Since their decay contributes to a TL glow peak above 350°C, this system is also interesting with respect to dosimetric applications.