[en] Trap level spectroscopy studies of alkaline-earth sulphate (CaSO₄ and SrSO₄) phosphors doped with ²³⁹Pu were carried out using electron paramagnetic resonance (EPR) and thermally stimulated luminescence (TSL) techniques. Internal (in situ) α-irradiation (from the α-decay of ²³⁹Pu) and external γ-irradiation studies carried out using EPR revealed the formation of radicals SO₂^-, O^-, O₃^-, SO₄^-, etc, in these matrices under different conditions. SO₂^- dimer formation is detected for the first time in alkaline-earth sulphates on γ-irradiation at 77K. The thermal stabilities of the radical ions (monitored using EPR) and their correlation with TSL glow peaks helped to identify the thermally stimulated free-radical reactions which result in luminescence and were characterised by the activation energy and frequency factor obtained from the analysis of TSL glows. (author)