Comparing the output of measured and GEANT4 simulated X-ray tubes

Monte Carlo simulation codes that model particle interactions with matter, including GEANT4, can be used to support the development of novel X-ray tubes and instruments for applications in industry and research. Based on our knowledge, simulations of the output of transmission-geometry X-ray tubes have not yet been conducted in GEANT4. Simulations of reflection-geometry tubes are scarce, with a limited number of studies investigating the capability and accuracy of GEANT4 in this domain. Therefore, the aim of this work is to benchmark GEANT4 for the characterisation of X-ray tubes with industry applications, using for the first time a range of X-ray tubes geometries and high voltages. In this work, GEANT4 is benchmarked against experimental measurements performed at the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia, with both transmission and reflection X-ray tubes. High voltages between 17 kV and 42.5 kV for tungsten, molybdenum, gold, and silver targets are investigated. The measurements have been performed with a MXR packaged X-ray tube (reflection) and Magnum X-ray tubes (transmission) and a fast silicon drift detector (SDD). Our study shows that GEANT4 predicts the bremsstrahlung continuum output of transmission and reflection X-ray tubes, in agreement with the experimental measurements. The Penelope physics models, distributed with GEANT4, and the GEANT4 X-ray fluorescence data libraries ANSTO HF, based on the Hartree-Fock approach, exhibit the best agreement against experimental measurements. Depending on the high voltage, target and X-ray line agreement was found to vary between 10% and 300%. Differences between GEANT4 and experimental data are more significant for lower voltage X-ray tube measurements and are most likely due to limitations in the ionization electron cross-section and/or atomic relaxation data libraries used. As next steps, it is recommended to validate GEANT4 against other, independent experimental measurements to corroborate the results of this work. In addition, it would be useful to repeat the same study with other general purpose Monte Carlo codes for radiation physics to compare their capability against GEANT4 in this application domain.