Water and tissue equivalence properties of biological materials for photons, electrons, protons and alpha particles in the energy region 10 keV–1 GeV: a comparative study

<b>Purpose:</b> To compare some biological materials in respect to the water and tissue equivalence properties for photon, electron, proton and alpha particle interactions as means of the effective atomic number (<i>Z_eff</i>) and electron density (<i>N_e</i>). <b>Methods:</b> A Z-wise interpolation procedure has been adopted for calculation of <i>Z_eff</i> using the mass attenuation coefficients for photons and the mass stopping powers for charged particles. <b>Results:</b> At relatively low energies (100 keV–3 MeV), <i>Z_eff</i> and <i>N_e</i> for photons and electrons were found to be constant while they vary much more for protons and alpha particles. In contrast, <i>Z_eff</i> and <i>N_e</i> for protons and alpha particles were found to be constant after 3 MeV whereas for photons and electrons they were found to increase with the increasing energy. Also, muscle eq. liquid (with sucrose) have <i>Z_eff</i> and <i>N_e </i>values close to the Muscle Skeletal (ICRP) and Muscle Striated (ICRU) within low relative differences below 9%. Muscle eq. liquid (without sucrose) have <i>Z_eff</i> and <i>N_e</i> values close to the Muscle Skeletal (ICRP) and Muscle Striated (ICRU) with difference below 10%. <b>Conclusions:</b> The reported data should be useful in determining best water as well as tissue equivalent materials for photon, electron, proton and alpha particle interactions.