Rayleigh and Compton scattering analysis for PMMA in the mammography energy range

Abstract

The method of obtaining the primary x-ray spectrum by the Compton scattering correction has been practically established for relatively high x-ray tube voltages. However, for mammography, the tube voltages are less than 30 to 35 kV and there exists an intense characteristic x-ray peak at 17.5 keV from the molybdenum target. The influence of Rayleigh scattering can not be neglected in this mammography energy range. Accurate data of Rayleigh and Compton cross sections for the scatterer material are required for obtaining the primary x-ray spectrum by correcting the scattered x-ray spectrum of mammography. The purpose of this study is to investigate the Rayleigh and Compton scattering cross sections for PMMA scatterer material in the mammography energy range theoretically and experimentally. Fluorescent x-rays of 15 to 25 keV were generated by exciting four metal targets including molybdenum by synchrotron radiation. The produced fluorescent x-rays were incident on a sphere of PMMA (polymethyl methacrylate), and scattered x-rays at 90, 120, 150, and 165 degrees, respectively, were measured with a CdTe detector. The scattered fluorescent x-ray spectrum was separated into the Rayleigh and Compton scattering peaks by using a curve fitting technique with two Gaussian functions. We compared the measured cross section data to those obtained from theoretical values. In addition, we calculated the scattered fluorescent x-ray spectra using the Monte Carlo simulation and compared them to the measured spectra. As a result, the ratio of the Rayleigh to the total scattering ratio agreed to theoretical value within 10%. The shapes of the scattered spectra calculated by Monte Carlo simulation agreed fairly well with those of measured spectra.