Electron spin resonance evaluation of pure CaSO₄ and as a phosphor doped with P and Dy

Polycrystalline CaSO₄ powder, doped with different elements but mainly rare earths, is one of the most interesting thermoluminescent (TL) materials. Although many electron spin resonance (ESR) analyses have been reported for these materials few studies have been published about the potential of CaSO₄ for ESR dosimetry; almost all studies used CaSO₄:Dy with a very low Dy concentration as the material for TL measurements. Pure CaSO₄ from Merck was used to prepare CaSO₄:Dy and CaSO₄:P:Dy with different Dy concentrations. Samples were annealed at 600°C for 1 h before irradiation in a Gammacell 220 irradiator with a ⁶⁰Co gamma source at a dose rate of 100 Gy.min^-1. The ESR spectra of the pure CaSO₄ and CaSO₄ doped with P and Dy show the lines usually observed with these types of material, with the factor g around 2.036 and an intense line at g = 2.0011 found only in the pure material. This line, probably an axial SO₄^-, grows linearly with absorbed dose until 1.0 kGy and shows good stability with time. The line should be stabilized by matrix impurities because it can be removed by a simple treatment with hot sulphuric acid.