Evaluation of scatter-to-primary ratio in soil CT-imaging

Tomography refers to the cross-sectional imaging of an object from transmission data collected by illuminating the object from many different directions. The mathematical algorithms for tomography reconstructions are based on projection data, which represent the attenuation of photons through an object. Projection data are a result of interaction between the radiation used for imaging and the substance of which the object is composed. The incident beam undergoes attenuation as it travels through an object. This attenuation is due to photons either being absorbed by the atoms of the material, or being scattered away from their original directions of travel. The ideal tomographic image consists of the photons which have not interacted within the object. However, many scattered photons which are produced from scattering interactions within the object are also recorded along with the desired photons. Radiation scatter leads to a type of error in the measurement of a projection that limits the image quality. The present work will focus on reconstruction errors due to scattering in soils. The EGS4 (Electron-Gamma Shower) system of computer codes was used, which is a general purpose package for Monte Carlo simulation of the coupled transport of electrons and photons in an arbitrary geometry for particles with energies above a few keV up to several TeV. Monte Carlo analysis was used to examine the spatial properties of scattered radiation in pencil beam geometry. Generally, scatter is measured in terms of the scatter-to-primary ratio (S/P). In this work, different soil samples were simulated and values of S/P for them have been studied. The distribution of S/P was calculated for several thickness to each soil, in order to simulate a cylindrical geometry and to determine the significance of detected scattered radiation in tomographic image. Two different photon energies were used: 60 keV and 662 keV. The dependence of S/P on soil diameter, chemical composition, bulk density and energy photon is presented. (author)