Abstract-The effective linear attenuation coefficients and build-up factors for single shield of Al, Fe, Pb, and for multi-layer shield of Al-Pb, Al-Fe, Fe-Pb, Al-Fe-Pb as a function of shield thickness, atomic number, and order of the materials composing the shield are investigated for two photon energies of 0.662 MeV and 1.25 MeV. Two derived practical formulas to calculate the effective attenuation coefficient and build-up factor for multilayer shields are used. It is noticed that changing the order of the materials among the shield has no significant effect on the experimental result. Measurement agrees well with the trend of the suggested formulas for calculating the effective attenuation coefficient and the buildup factor. The linear attenuation coefficient is observed to have a strange dependency with the atomic number and photon energy. For single layer shield, the attenuation coefficient increases with decreasing atomic number at low photon energy and increasing with increasing atomic number at high photon energy.

No abstract

This study investigates the possibility of achieving unity energy response using the very sensitive CaSO4:Dy/Teflon thermoluminescent detector at photon energies below 100 keV. Accurate measurements for the energy responses were carriedout using ultra thin, 3 micron thick, TLD discs with average grain size of about 3𝝁𝒎. The present work shows that the experimental reduction factor for the 15 % phosphor loading with average grain size of 3 𝝁𝒎 is in good agreement with the calculation based on the cavity theory but at grain size of 1.0 𝝁𝒎. This indicates that the cavity theory is underestimating the real experimental reduction factor in the energy response. The present work expect that unity energy response can be achieved with grain size of about 𝟏 𝝁𝒎.

Accurate measurement was carried out for the dose gradient in Teflon irradiated with filtered X-ray spectra having effective energies of 40 keV and 55 keV when in contact with aluminum, titanium, copper, and tin. At low photon energies, the interface region is only extended for about 10 microns from the interface, therefore, ultra-thin LiF/Teflon discs of the order of 3 microns thick was developed and used to measure directly the dose gradient in Teflon. Due to the relatively large slope of the depth dose curves near the interfaces, a displacement correction factor was introduced to determine the effective measuring point of the detector. A fitting exponential formula is suggested and used to estimate the dose gradient for Bone-Teflon interface. The interface dose for Bone-Teflon is 3.8 times the equilibrium dose at 70 KV, while it is about 3.1 at 100 KV.