Effective atomic number and electron density of amino acids within the energy range of 0.122–1.330 MeV Chaitali V. More n , Rajkumar M. Lokhande, Pravina P. Pawar n Department of Physics, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad, Maharashtra 431004, India HIGHLIGHTS  Gamma-ray interaction studies have been performed using narrow-beam good geometry set-up.  The values of parameters μ m , s t , ε, s e , Z eff , and N eff were calculated.  All experimental data were compared with the XCOM program.  Measured data of amino acids are useful in various fields including biomedicine. article info Article history: Received 24 September 2015 Received in revised form 8 February 2016 Accepted 25 February 2016 Available online 9 March 2016 Keywords: Mass attenuation coefficient Total atomic and electronic cross sections Effective atomic number Effective electron density Molar extinction coefficient abstract Photon attenuation coefficient calculation methods have been widely used to accurately study the properties of amino acids such as n-acetyl-L-tryptophan, n-acetyl-L-tyrosine, D-tryptophan, n-acetyl-L- glutamic acid, D-phenylalanine, and D-threonine. In this study, mass attenuation coefficients (m m ) of these amino acids for 0.122-, 0.356-, 0.511-, 0.662-, 0.884-, 1.170, 1.275-, 1.330-MeV photons are determined using the radio-nuclides Co 57 , Ba 133 , Cs 137 , Na 22 , Mn 54 , and Co 60 . NaI (Tl) scintillation detection system was used to detect gamma rays with a resolution of 8.2% at 0.662 MeV. The calculated attenuation coefficient values were then used to determine total atomic cross sections (s t ), molar extinction coeffi- cients (ε), electronic cross sections (s e ), effective atomic numbers (Z eff ), and effective electron densities ( N eff ) of the amino acids. Theoretical values were calculated based on the XCOM data. Theoretical and experimental values are found to be in a good agreement (error o5%). The variations of m m , s t , ε, s e , Z eff , and N eff with energy are shown graphically. The values of m m , s t , ε, s e are higher at lower energies, and they decrease sharply as energy increases; by contrast, Z eff and N eff were found to be almost constant. & 2016 Elsevier Ltd. All rights reserved. 1. Introduction Mass attenuation coefficients, total atomic and electronic cross sections, molar extinction coefficients, effective atomic numbers, and effective electron densities are critical in applied as well as funda- mental science because of their diverse applications in oncology, shielding, gamma-ray fluorescence studies and tomography. Hydrogen-, carbon-, nitrogen-, and oxygen-based compounds that is, biological molecules such as carbohydrates, proteins, lipids, enzymes, vitamins, nucleotides, and hormones, are involved in a variety of physiological functions of living systems. Amino acids are the building blocks of proteins, which are the most abundant mac- romolecules in the living cells and constitute the largest function of living matter in all types of cells. Interaction of photons with biolo- gical molecules plays an important role in radiation biology, nuclear technology, and space research as radioactive sources such as Co 57 (122 keV), Ba 133 (356 keV), Na 22 (511 and 1275 keV), Cs 137 (662 keV), Mn 54 (840 keV) and Co 60 (1170 and 1330 keV) are used in biological studies, radiation sterilization, and industry (Hall, 1978). A deep un- derstanding of the interaction of photons with biologically important substances such as amino acids, fatty acids, and carbohydrates is desirable. Photons in the energy range of kilo-electron-volts are important in radiation biology, medical diagnostics, and therapy (Hubbell, 1999). Photons in the mega-electron-volt range are vital for radiography and medical imaging, where the cross-sectional anat- omy is generated by computer-aided tomography(CAT), and photons in the giga-electron-volt energy range are important in astrophysics and cosmology (Manohara et al., 2008). Mass attenuation coefficient (m m ) is a measure of the average number of interactions between incident photons and matter that Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/radphyschem Radiation Physics and Chemistry http://dx.doi.org/10.1016/j.radphyschem.2016.02.024 0969-806X/& 2016 Elsevier Ltd. All rights reserved. n Corresponding authors. E-mail addresses: chaitalimore89@gmail.com (C.V. More), pravinapawar4@gmail.com (P.P. Pawar). Radiation Physics and Chemistry 125 (2016) 14–20