Energy dependence of effective atomic numbers for photon energy absorption of vitamins

Abstract

Mass - Energy absorption coefficient, Effective atomic numbers for photon energy absorption (ZPEA,eff) and photon interactions (ZPI,eff), of 8 Vitamins viz., vitamin-A (Retinol), B2 (Riboflavin), B3 (Niacin), B7 (Biotin), B9 (Folic acid), B12 (Cobalamin), K1 (Phylloquinone) and P (Flavonoids) were computed for the energy range 1 keV to 20 MeV. Variation of these parameters has been studied as a function of incident photon energy. The ZPEA,eff and ZPI,eff values have been found to change with energy and composition of the biological molecules. The variations of mass energy-absorption coefficient, effective atomic number for photon interaction ZPI,eff and ZPEA,eff with energy are shown graphically. The substantial deviation occurs among ZPEA,eff and ZPI,eff in the energy range 5-100 keV for Retinol and Phylloquinone. The deviation is also observed for Riboflavin, Niacin, Folic acid, Flavonoids in the energy range 8 -100 keV, and for Biotin (15-150 keV) and for Cobalamin (6-200 keV). The substantial change occurs between ZPEA,eff and ZPI,eff which represents the absorbed dose, it is preferable to use ZPEA,eff instead of ZPI,eff in medical radiation dosimetry for the calculation of absorbed dose in the literature, there are no reports on the study of ZPEA,eff of selected vitamins. This inspired us to carry out the present work. In the present work, the ZPEA,eff has been calculated for selected vitamins namely Vitamin-A (Retinol), B2 (Riboflavin), B3 (Niacin), B7 (Biotin), B9 (Folic acid), B12 (Cobalamin), K1 (Phylloquinone) and P (Flavonoids) by a direct method in the energy region of 1 keV to 20 MeV using the µen/ρ values from the compilation of Hubbell and Seltzer 1 . The ZPEA,eff and ZPI,eff values have been found to change with energy and composition of the vitamins. The variations of ZPEA,eff and ZPI,eff with energy are shown graphically. The reasons for using ZPEA,eff rather than the commonly used ZPI,eff in medical radiation dosimetry for the calculation of absorbed dose in radiation therapy are discussed. The effect of absorption edge on ZPEA, eff and its variation with photon energy and the possibility of defining two set values of these parameters below the K-absorption edge of high-Z element present in the Biotin and cobalamin are discussed.