Dosimetry of very low energy photons

Until recently, dosimetry of photons below 20 keV has not been comprehensively 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 10-4 to 1 g/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. CaS04, CaF2, LiF, Li2B407, in the same energy region is presented in terms of the photon energy absorption coefficients. (author)