Studies on effective atomic number, electron density and kerma for some fatty acids and carbohydrates.

The effective atomic number, Z(eff), the effective electron density, N(el), and kerma have been calculated for some fatty acids and carbohydrates for photon interaction in the extended energy range from 1 keV to 100 GeV using an accurate database of photon-interaction cross sections and the WinXCom program. The significant variation of Z(eff) and N(el) is due to the variations in the dominance of different interaction processes in different energy regions. The maximum values of Z(eff) and N(el) are found in the low-energy range, where photoelectric absorption is the main interaction process. The minimum values of Z(eff) and N(el) are found at intermediate energies, typically 0.05 MeV < E < 5 MeV, where Compton scattering is dominant. In this case, Z(eff) is equal to the mean atomic number of the bio-molecule. Wherever possible, the calculations are compared with experimental results. A comparison is also made with the single values of the Z(eff) and N(el) provided by the program XMuDat. It is also observed that carbohydrates have a larger kerma than fatty acids in the low-energy region, where photoelectric absorption dominates. In contrast, fatty acids have a larger kerma than carbohydrates in the MeV range, where Compton scattering is the main interaction process.