Features of EPR dosimetry with CaSO4:Dy phosphor

The electron paramagnetic resonance(EPR) technique was used to study the paramagnetic centers induced by ionizing radiation in thermoluminescent CaSO4:Dy. Two different radiation induced centers, detectable in the (1-10(7)) Gy dose range and attributed to (SO3)- and Ca-vacancy center, (VCa)2-, respectively, can be used for dosimetry purpose. The (VCa)2- center is detectable only upon sample annealing at temperatures higher than about 180 degrees C. A reliable dose assessment can be performed in the (1-10(7)) Gy dose range and likely over 10(7) Gy. The sensitivity decreases with thermal cycles, while the yield of both centers increases with accumulated dose (pumping effect), at a greater extent for (VCa)2- center. (VCa)2- center is stable with time, while (SO3)- center shows a dose-dependent fading. Among the applications that can be imaged for this dosimeter, very high dose assessment capability is of particular importance.