CaSO4:Dy and CaSO4:Ce,Eu intrinsic efficiencies dependence on ionizing radiation type and quality

Abstract

The dependence of a thermoluminescent (TL) dosimeter response to the type and quality of radiation is a key issue that is being tackled worldwide by the development of new dosimetric materials associated with this technique. In this context, the aim of the present work is to evaluate the intrinsic efficiency of CaSO4:Dy, considered as the standard material, and CaSO4:Ce,Eu, a newly developed TL material, for different ionizing radiation types and energies. To do so, a batch of 55 dosimeters of each material was selected according to their non-irradiated TL readout and intrinsic efficiency to the 60Co -radiation on air and electronic equilibrium conditions and then divided into eleven sets of five dosimeters, one of the sets being kept as the control set to evaluate the non-irradiated TL signal while the ten remaining sets were irradiated, again in air and electronic equilibrium conditions, with doses ranging from 0:1 mGy to 10 Gy in secondary standards 60Co and 137Cs - radiation sources, RQR, RQA and RQT ISO/IEC 61267 series and N ISO 4037 series X-ray beams, always including the reference quality for the radiation beam series, and tertiary standard collimated electron beams with effective energies from 4 MeV to 20 MeV. AThermo (Harshaw) 3500 thermoluminescent reader was used to evaluate TL readouts 24 h after the irradiation and the obtained glow curves were exported in the ASC format through WinREMS TL reader controller associated software. Individual peak intensity, integrated response, peak to peak intensity ratio, calibration curves and intrinsic efficiency, provided that all dosimeters are 0:8 mm thick pellets of 6:0 mm of diameter containing 16:67 mg of TL material, were calculated with the aid of SciLab 5.5.2 software, also used to graphically explore the behaviour of CaSO4:Dy and CaSO4:Ce,Eu intrinsic efficiencies with the radiation type or the radiation quality. As expected from literature, CaSO4:Dy intrinsic efficiency presented a dependence of up to 30% with radiation type or quality while CaSO4:Ce,Eu intrinsic efficiency varied by 200% with radiation quality. Despite this huge dependence, the CaSO4:Ce,Eu peak I to peak II intensity ratio remains stable with the radiation type and varies by 5% from one radiation type to another, so that this newly developed TL material can be used as a dosimeter capable of determining, in non-mixed radiation fields and after an adequate and rigorous calibration, both radiation type and quality besides the dose.