Effective atomic numbers for photon energy absorption of some low- Z substances of dosimetric interest

Abstract

Effective atomic numbers for photon energy absorption (Z pea eff) and effective atomic numbers for photon interaction (Z pi eff) of some low- Z substances of dosimetric interest such as A-150 tissue-equivalent plastic (A150TEP), alanine, bakelite, Gafchromic sensor (GS), plastic scintillator (PS), polyethylene, mylar, polystyrene, perspex, radiochromic dye film nylon base (RDF : NB), tissue-equivalent gas-methane based (TEG : MB) and tissue-equivalent gas-propane based (TEG : PB) have been calculated by a direct method in the energy region of 1 keV–20 MeV. Experimental mass attenuation coefficients and Z pi eff of some of these substances at selected photon energies of 26.34, 33.2, and 59.54 keV have been obtained and compared with theoretical values. The Z pea eff and Z pi eff values steadily increases up to 6–15 keV, and then they steadily decrease up to 600–1500 keV for all the substances studied. From 1.5 MeV, the values increases with increase in energy up to 20 MeV. Significant differences up to 33.68% exist between Z pi eff and the Z pea eff in the energy region of 10–150 keV. The single effective atomic numbers obtained using the program XMuDat (Z xmudat eff ) are found to be significantly higher compared to those of Z pea eff and Z pi eff values in the entire energy of interest for all the substances studied. The directly calculated Z pea eff and Z pi eff values vary with energy compared to the energy-independent effective atomic numbers predicted by various theoretical expressions. The effects of absorption edges on effective atomic numbers and their variation with photon energy and the possibility of defining two set values of effective atomic numbers below the absorption edges of elements present in the composite substances are discussed.