Optimization of transmission target x-ray tubes for imaging applicationsusing Monte Carlo-based methods,

摘要

Abstract: A low energy electron expansion of the EGS4 code system (briefly called EGS4/GOS) has been used in the simulation of X-ray tubes operating at diagnostic energies. In this new code, electron-atom inelastic collisions take into account atomic binding effects, and the emission of K-fluorescence radiation is simulated fully. Improved models for the generation of bremsstrahlung radiation in condensed media have also been developed. Benchmarks against experimental data show that the new code simulates realistically the production of bremsstrahlung and fluorescence radiation in X-ray tubes, with an accuracy of the order of 10% for the K$-$alpha$/ line. The EGS4/GOS code has been used in studies aimed at understanding the physics that constrains transmission target X-ray tubes. In a first set of studies, the tube's operational characteristics (namely the efficiency and the ratio of fluorescence to bremsstrahlung radiation in the measured spectrum) have been evaluated. It is shown that tubes with thinner targets exhibit higher fluorescent-to-bremsstrahlung ratios (F/B), but this gain is paid for in terms of a loss in efficiency. Further results indicate that increased tube voltages benefit both the tube efficiency and F/B. The choice of substrate materials for thin target applications is also discussed. It is shown that low Z materials, where the probability for generating bremsstrahlung radiation is low, may represent feasible alternatives. However, these materials also turn out to be more transparent to low energy radiation, and this may reduce the observed fluorescence-to- bremsstrahlung ratios. The effectiveness of different filter materials to be used in the development of 'quasi- monochromatic' X-ray tubes is also discussed. !32