[en] In the recently developed high-sensitive CaSO₄:Dy phosphor, sieving before the high-temperature sintering treatment has successfully eliminated particle agglomeration during subsequent sintering, and has further enhanced its thermostimulated luminescence (TSL) sensitivity to γ-rays. The reduction in TSL sensitivity of higher sized grains observed earlier following the procedure of sieving after sintering has also more or less vanished. Maximum TSL sensitivity is seen after sintering around 700 deg. C, whereas maximum photoluminescent (PL) sensitivity is seen after sintering around 325 deg. C. While the observed increase in TSL sensitivity (by 30%) with increasing sintering temperature in the range 325-700 deg. C is explained on the basis of diffusion of Dy³⁺ ions from the surface to the whole volume of the grains (0-75 μm), the drastic decrease (by a factor of 3) in PL sensitivity with increasing sintering temperature is explained on the basis of change in the Dy³⁺ environment on the grain surface perhaps due to oxygen incorporation. Washing with water and acetone, which affect mainly the surface traps, enhances the PL sensitivity of CaSO₄:Dy slightly; however, it does not influence TSL sensitivity very significantly. Grinding reduces PL in general, but no such trend was noticed in TSL which supports the conclusion that PL originates mainly from surface traps since grinding affects mainly the grain surface. However, the sharp reduction in TSL and PL sensitivities observed at 400 deg. C indicates that an unusual process takes place near that sintering temperature. (author)