The effective atomic numbers of some biomolecules calculated by two methods: A comparative study

The effective atomic numbers Z(eff) of some fatty acids and amino acids have been calculated by two numerical methods, a direct method and an interpolation method, in the energy range of 1 keV-20 MeV. The notion of Z(eff) is given a new meaning by using a modern database of photon interaction cross sections (WinXCom). The results of the two methods are compared and discussed. It is shown that for all biomolecules the direct method gives larger values of Z(eff) than the interpolation method, in particular at low energies (1-100 keV) At medium energies (0.1-5 MeV), Z(eff) for both methods is about constant and equal to the mean atomic number of the material. Wherever possible, the calculated values of Z(eff) are compared with experimental data. (C) 2009 American Association of Physicists in Medicine. [DOI: 10.1118/1.3030952]