Studies on response of LiMgPO4:Tb, B TEFLON embedded OSL discs to beta particles

RPAD, Bhabha Atomic Research Centre has developed LiMgPO4:Tb,B (LMP), an optically stimulated luminescent (OSL) phosphor which has high sensitivity and wider dose linearity. Teflon embedded LMP discs (0.4 mm thick) were prepared and found suitable for dosimetry applications. In view of this, studies on response of Teflon embedded LMP discs to beta particles were carried out. Dosimeters were irradiated using PTB beta secondary standard calibration setup (BSS2) which contains three beta sources viz. 147Pm (224 keV), 85Kr (687 keV) and 90Sr/90Y (2280 keV). Various beta doses in the range from 1 mSv -500 mSv were delivered to LMP discs and response was studied by covering LMP discs using various filters viz 50 μm, 80 μm and 180 μm Mylar, 1 mm Perspex and 1.6 mm Perspex. The response of OSLD discs was also compared with the response of the standard TLD badge (0.8 mm thick Teflon embedded CaSO4:Dy discs) currently used in India for personnel monitoring applications. CWOSL (continuous wave optically stimulated luminescence) measurements were carried out using RISO TL/OSL system TL/OSL-DA-15 in which a cluster of 42 blue light emitting diodes (ë = 470 ± 30 nm) were used for stimulation. CWOSL curves were recorded for 60 s. The relative response with respect to 137Cs photons for 0.4 mm thick LMP discs to various beta sources were found to be ∼ 8%, ∼ 53.5% and 100 % respectively for 147Pm, 85Kr and 90Sr/90Y beta energies. In addition, the response of LMP discs under various filter combinations was studied and ratio of the response of open disc to the response under filter for above beta energies was also estimated. This study was necessary as these ratios are useful to estimate the energy of beta particles and are also used to apply correction factor while evaluating beta dose/or in the design of dose estimation algorithms. It is worth mentioning that for 147Pm and 85Kr, the response of Teflon embedded LMP (0.4 mm thick) discs is energy dependent because the disc thickness (0.4 mm, ∼ 130 mg/cm2) is more than the range of the beta particles emitted by 147Pm and 85Kr. However, the beta response of the 0.4 mm thick LMP discs was found to be better than the response of presently used TLD badge in which discs are 0.8 mm thick. Hence, 0.4 mm thick LMP discs might be well suited for personnel monitoring applications for beta energies greater than 0.4-0.5 MeV. (author)