THE EFFECT OF SCATTERED RADIATION IN X-RAY TECHNIQUES- EXPERIMENTS AND THEORETICAL CONSIDERATIONS

摘要

Theoretical and experimental investigations have been carried out to study the scattered radiation for energies usually used in radiography. Monte Carlo calculations have shown nonuniform contribution of the scattered radiation to the total flux for large thickness variations, i.e. on edges of plates. These theoretical results were taken occasion to investigate experimentally the theoretical predictions. The presented experimental results obtained for a plate geometry confirm the theoretical findings. For interpretation purposes a simplified two-dimensional scattering model was developed accounting for the first scattering event while neglecting multiple scattering. This model includes a quantitative description of the finite size of the detector including the collimator. It was shown that the model is able to describe the experimental results in a quantitative manner. By applying the developed model the influence of the material properties in terms of the mean free path relative to the plate thickness was investigated. Conclusions are drawn which confirm the physical interpretation of the results from Monte Carlo calculations and the integral transport approach. The theoretical and experimental results show restrictions for the applicability of ray tracer models together with constant built-up factors. If material parameters are changed on a small scale compared to the mean free path the built-up factor approach is accurate enough to describe radiographic techniques. In case of large scale discontinuities more precise scattering models have to be chosen describing the nonuniform contribution of the scattered flux to the total photon flux.