An approach for obtaining the intensity of the radiation transmitted through a scatterer Niyazi Meric ¸ ∗ ) Department of Engineering Physics, Faculty of Engineering, Ankara University, 06100, Be¸ sevler – Ankara, Turkey Received 30 December 2004; final version 28 February 2005 Monte Carlo simulation was applied to the investigation of intensity of the radiation transmitted through a scatterer. Simulations consisted of a pencil beam of monoenergetic photons with energies from 50keV to 10meV incident on water, aluminium, iron, cop- per, tin and lead slabs. We determined the scattered radiation and the scatter fractions recorded in the detector plane. An empirical formula, which is a function of the physical parameters scatterer thickness, the linear attenuation coefficient, and the atomic number was obtained for intensity of radiation transmitted through a scatterer. PACS : 87.53.Wz Key words : Monte Carlo, monoenergetic photon, transmitted radiation, scattered radia- tion, scatter fraction 1 Introduction In the transmission radiography,the x-rays reaching the detector plane consist of unscattered (primary) and scattered components. While the primary fluence contributes to the signal in the resulting image, the scattered fluence can reduce the contrast and introduce an additional noise. In order to estimate the influence of the scattered radiation on the image quality, the physical characteristics of the scattered radiation must be known. As x-rays traverse in medium, they may be absorbed, pass through without interaction (primary photons), or be scattered. The number of primary photons N P that strike a detector after passing through a scatterer of thickness L is given by N P = N 0 e -μL , (1) where μ is the linear attenuation coefficient for scatterer at energy E and N 0 is the number of the incident photons. This equation is valid only if the attenuation coefficient is actually a constant, which is true only if all of the photons in the incident beam have the same energy (a monoenergetic beam) and the beam is narrow. Some photons may be scattered by the scatterer so that they reach the detector,withtheresultthatthenumberofthetransmittedphotonswillappearto be larger than primary photons. This situation is usually accounted for replacing Eq. (1) by the following equation: N T = N 0 e -μL K(L, E) . (2) * ) E-mail: meric@ankara.edu.tr Czechoslovak Journal of Physics, Vol. 55 (2005), No. 8 1025