Influence of the PMMA slab and ISO water phantom in calibrating personal dosimeter in the energy range of 36-662 keV

Personnel dosimeter calibration for the determination of operational quantities used in individual monitoring requires placement on a phantom that provides a reasonable approximation to the backscatter properties of the part of the body on which it is worn. The personal dose equivalent Hp(d) is defined in the human body which is not a measurable quantity. The reference International Commission on Radiation Units and Measurements (ICRU) tissue is not readily available; hence a phantom of alternative must be used for calibration. The well recognized polymethylmethacrylate (PMMA) slab phantom of size 30x30x15 cm³ are still being used in calibrating personal dosimeters. The International Organization for Standardization (ISO)-4037(3) has proposed another phantom of the same size as ICRU, which is named as ISO water phantom. In the present study, calibrated X-ray fields are characterized for National Institute of Advanced Industrial Science and Technology (AIST) middle beam spectrum series by which the influence of these proposed phantoms has been studied by the thermoluminescence dosimetry (TLD) technique. Discrepancies of responses within 8% have been observed at lower energies up to 42 keV. There is a very good agreement in responses is observed for ISO water slab and PMMA slab phantom for photon energies above 42 keV. Experimentally obtained correction factors for AIST radiation qualities of M50 and M60 for PMMA slab to ISO water phantom is proposed. Measured backscatter factor results from PMMA to ISO water-filled phantoms over the photon energy range 36 to 662 keV are reported. This shows that the new ISO water phantom is a better substitute of ICRU tissue phantom than the PMMA slab. (author)