LS-PGNAA(Large Sample Prompt Gamma Neutron Activation Analysis) is a noninvasive method for determination element fractions of large samples with an unknown homogeneous matrix composition .and when the sample is large, effects such as neutron self-shielding and gamma attenuation cause error in estimating amount of matter. For determination of amount of matter exactly, corrections should be considered, so correction factors for these effects are expressed. In this paper neutron self-shielding correction factor is calculated and its effect on correction of full energy peak in prompt gamma spectrum is investigated. For calculating this factor a simulation was carried out using MCNP code. samples put in cylindrical PTFE (poly tetra fluor ethylene) container .Effects of three different parameters: type of matter, dimension of sample and density of that, investigated on neutron self-shielding. also it has showed the area of full energy peak has linear relation with atom density of special sample and parameters of that line determined. Also it showed that by using self-shielding factor, parameters of fitted line obtain with less error.

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