[en] ESR measurements on x-irradiated undoped CaSO₄ single crystals at 77K reveal two related radiation damage centres. Step annealing measurements suggest a connection between these centres and the thermoluminescent glow peaks at approximately 395K and 465K. An analysis of the g values (Centre I; gsub(x) = 2.0006, gsub(y) 2.0091 and gsub(z) = 2.0395, Centre II; gsub(x) = 2.0011, gsub(y) = 2.0084 and gsub(z) = 2.0256) in conjunction with the known crystal structure indicates that the defects could result from the removal of an electron from a non-bonding orbital of a sulphate oxygen atom adjacent to a Ca²⁺ vacancy. The ESR signals related to these centres exhibit an unusual dependence on temperature and microwave power between 120K and 250K, which is attributed to a motional transition