Dosimetry of Very Low Energy Photons

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Until recently, dosimetry of photons below 20 keV has not been comprehen-sively attempted mainly because of the absence of photon cross-section data at these energies. In the present paper, photon attenuation and energy absorption coefficients for different materials have been compiled from various sources for energies in the range 1–50 keV. Absorbed fractions are obtained from these data for a variety of tissue compositions (bone, muscle, liver, lung, brain, thyroid, adipose tissue) for spheres with radii varying from 10−1 to 1g/cm2 by a modified geometric factor approach. Variation of absorbed fraction with photon energy, size, and composition of the target has been studied. Inclusion of high Z materials such as calcium, iron, and copper in tissue compositions, even in small quantities, influences the absorbed fraction to exhibit the K-edge of the materials distinctly for small target masses. Photon energy-dependent response of various TLD materials, viz. CaSO4 CaF2, LiF, Li2 B4O7 in the same energy region is presented in terms of the photon energy absorption coefficients.

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