A study of effective atomic number and electron density of gel dosimeters and human tissues for scattering of gamma rays: momentum transfer, energy and scattering angle dependence.

The objective of this work was to study water- and tissue-equivalent properties of some gel dosimeters, human tissues and water, for scattering of photons using the effective atomic number (Z ). The Rayleigh to Compton scattering ratio (R/C) was used to obtain Z and electron density (N ) of gel dosimeters, human tissues and water considering a 10-10 momentum transfer, q (Å). In the present work, a logarithmic interpolation procedure was used to estimate R/C as well as Z of the chosen materials in a wide scattering angle (1°-180°) and energy range (0.001-100 MeV). The Z of the chosen materials was found to increase as momentum transfer increases, for q > ~1 Å. At fixed scattering angle and energy, Z of the material first increases and then becomes constant for high momentum transfers (q ≥ 3 Å), which indicates that Z is almost independent of energy and scattering angle for the chosen materials. Based on the Z data and the continuous momentum transfer range (10-10 Å), MAGIC, PAGAT and soft tissue were found to be water-equivalent materials, since their differences (%) relative to water are significantly low (≤3.2 % for MAGIC up to 10 Å, ≤2.9 % for PAGAT up to 10 Å, and ≤3.8 % for soft tissue up to 10 Å), while the Fricke gel was not found to be water equivalent. PAGAT was found to be a soft tissue-equivalent material in the entire momentum transfer range (<4.3 %), while MAGAT has shown to be tissue equivalent for brain (≤8.1 % up to 10 Å) and lung (<8.2 % up to 10 Å) tissues. The Fricke gel dosimeter has shown to be adipose tissue equivalent for most of the momentum range considered (<10 %).