IOSR Journal of Applied Physics (IOSR-JAP) e-ISSN: 2278-4861.Volume 8, Issue 3 Ver. III (May. - Jun. 2016), PP 23-27 www.iosrjournals.org DOI: 10.9790/4861-0803032327 www.iosrjournals.org 23 | Page Determination of Effective Atomic Number of Some Bimolecules for Electron Interaction. S.Ramesh Babu* 1 , Mutturaj M Hosamani 2 , Santosh Mirji 3 , N.M. Badiger 4 1,2,3,4 Department of Physics, Karnatak University, Dharwad, India 580 003 Abstract: The effective atomic number of biomolecules such as carbohydrates and carboxylic acids for electron interaction at the energy of 942 keV have been determined by measuring their mass stopping power, using a Si(Li) detector coupled to 8K multichannel analyzer. The mass stopping power are determined by measuring the energies of incident electrons and transmitted electrons in the biomolecules. From the measured mass stopping power, the effective atomic numbers of the biomolecules have been determined and compared with theoretical values for electron interaction and photon interaction. Keywords: Internal Conversion (IC), Mass Stopping Power (MSP), Effective Atomic Number (Z eff ) I. Introduction Effective atomic number (Z eff ) is widely used in radiation studies, particularly for characterizing the interaction processes in alloys, biological tissues and substitute materials. Hine [1] has pointed out that the atomic number of a composite material varies with the type of radiation and energy of the radiation with which it interacts. Effective atomic number can be defined as a weighted arithmetic mean of the atomic number of the constituent atoms. This weighing factor accounts for the type of radiation, material and interaction cross section. Several authors have determined the Z eff for photon interaction (Z eff,pi ) at different energy ranges for various materials like semiconductors, polymers, inorganic compounds, alloys, dosimetric materials, thermo luminescence materials, biological samples and biological molecules as listed by Manohara et al., [2] . Manjunathaguru et al., have derived semi empirical formula by matrix method to calculate Z eff,pi of biologically important compounds containing H,C,N,O in the energy range of 145 -1330 keV [3] and 6.4- 136 keV [4] . Manohara et al., [5] have devised a comprehensive set of formulas for all types of materials and photon energies above 1 keV. Recently Singh and Badiger have compared various methods of calculating Z eff of human organ tissue substitutes [6] . Unlike Z eff,pi, the studies on Z eff for electron interactions, Z eff,ei, are very few. White [7] was the first to analyze the photon interaction and electron interaction in the matter and showed that Z eff differs for photon and electron interactions. Parthasarathy et al., [8] have calculated Z eff of biological materials for photon, electron and He ions. Recently Kurudirek et al., [9] have calculated Z eff of many essential biomolecules for the photon, electron, proton and alpha particle interactions; the calculations are carried out for a variety of therapeutically significant energy ranges. Taylor et al., have calculated the Z eff for radiative, collisional and total electron interaction processes in gel dosimetric materials [10] and in TLD-100 and TLD-100H dosimetric materials [11] over a wide range of energy. All these authors obtained the Mass Stopping Power (MSP) values either from ICRU report-37 [12] or from ESTAR [13] and then established the relation between MSP and Z of the elements; the Bragg additivity law is used to compute the MSP of the sample. The Z eff,ei of the sample is taken as the Z corresponding to the MSP of the sample in the Z vs MSP plot of the elements. It is well known that the Bragg additivity law does not account for environmental effect and hence experimentally determined the MSP values will undoubtedly give information about environmental effect. In the present work, we have measured the MSP using Si(Li) detector spectrometer and determined the Z eff,ei of some biological samples using empirical formula. II. Theoretical Background Theoretical values of Z eff,ei are calculated using standard formula as given below:   , =        /  (1) where (MSP)i, Ai &Fi are the MSP, mass number & molar fraction of the element i in the mixture or compound. Theoretical values of Z eff,pi are calculated using Auto-Zeff software [14] . This is user-friendly software written in visual basic to compute the average atomic numbers and spectral-weighted mean atomic numbers. It determines Z eff,pi by establishing the smooth correlation between the interaction cross-section and the atomic number. It uses a matrix of mass attenuation coefficients formed as a function of atomic number and photon energies ranging from 10 keV to 1 GeV. The cross-sections of a compound or mixture are calculated by linear additivity and their Z eff,pi by the interpolation of Z values between adjacent cross-section data.