Comparison of molar extinction coefficients of amino acids and fatty acids

Gamma ray and x-ray attenuation in liquid and solid solutions can with great advantage be analyzed in terms of the molar extinction coefficient, known from spectroscopy in the visible and near-visible spectral range. Most studies of interaction of photons with matter in the past have been concerned with solid absorbers. The use of absorber in the form of solution has some advantages: The criterion of homogeneity is automatically satisfied and the strength of the absorber can be changed by varying the relative amount of solute and solvent. In the present work the molar extinction coefficients, (e) of aqueous solutions of amino acids viz. Glycine (C2H5NO2), l-Serine (C3H7NO3), l-Theronine (C4H9NO3), l-Proline (C5H9NO2), l-Valine (C5H11NO2), l-Phenylalanine (C9H11NO2) and fatty acids viz: Formic acid (CH2O2), Acetic Acid (C2H4O2), Propionic Acid (C3H6 O2), Butyric Acid (C4H8O2), n-Hexanoic Acid (C6H12O2), n-Caprylic Acid (C8H16O2), Lauric Acid (C12H24O2), Myristic Acid (C14H28O2), Palmitic Acid (C16H32O2), Oleic Acid (C18H34O2) and Stearic Acid (C18H36O2) have been studied by narrow beam transmission geometry at photon energies in the range 81-1332 keV. The molar extinction coefficients of all samples were determined. The experimental results are found to be in good agreement with theoretical calculations and were independent of the density of the solution. The extinction coefficients of amino acids are fitted to the fourth order polynomial, where as the fatty acids are fitted to the third order polynomial. The measurements of gamma ray attenuation coefficients of solutions might be useful to quote the atomic cross sections in units of cm 2 /mol instead of the presently accepted units of barn/atom or barn/molecule