Studies on pelletised lithium magnesium borate TL material for eye lens dosimetry

Recent epidemiological studies in various cohorts confirm that radiation induced cataract may occur at a threshold dose as low as 0.5 Gy. ICRP has recognised the higher radiosensitivity of eye lens and recommended to reduce annual eye lens dose limit from 150 to 20 mSv. Present dosimetry for eye lens is largely based on LiF based dosimeters. The present work is an attempt towards using near tissue equivalent lithium borate material namely lithium magnesium borate doped with terbium (LMB:Tb) in eye lens dosimetry. The material in powder form was synthesised using solid state sintering method and pelletised using poly tetra fluoro ethylene (PTFE) as binding agent. It was observed that 130 mg of 1 mm thick LMB:Tb pellet bound with PTFE showed stable glow curve structure and attractive dosimetric features in terms of sensitivity, fading, linearity, reusability etc. A proposal of 1.5 mm Teflon encapsulation corresponding to tissue equivalent thickness of 3 mm was put forward for an ideal dosimeter for the measurement in terms of H_p(3). Energy and angular dependence studies based on FLUKA simulations suggest a flat response for the prototype design. In addition to PTFE, various tissue equivalent encapsulations such as polyimide, polyamide 6 and PMMA were also evaluated using FLUKA code.