26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Implementation of Distorted-Wave Born Approximation Calculated Electron Ionisation Cross Sections for X-ray Tube Simulations in Geant4

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral AIP | Atomic and Molecular Physics (ATMOP)

Description

Transmission geometry X-ray tubes are popular devices used in portable and specialised X-ray spectroscopy applications due to their small size and effectiveness at low power. However, purpose-built models for predicting their X-ray emission remain absent from the literature. Scientists requiring accurate transmission geometry X-ray tube models are currently limited to imprecise alternatives. Typical alternatives are specialised for modelling reflection geometry X-ray tubes which produce significantly different X-ray spectra.
This work uses Geant4, a Monte Carlo particle tracking toolkit, to simulate X-ray emission from transmission geometry X-ray tubes, and validates the use of alternative electron ionisation cross section values to improve predictive accuracy. Specifically, cross sections calculated via the distorted-wave Born approximation (DWBA) are used to replace Geant4's native plane-wave Born approximation (PWBA), which is shown to be insufficient for accurately modelling X-ray emission. Use of PWBA calculated cross sections is inadequate to model characteristic X-ray production at X-ray tube voltages close to characteristic radiation excitation edges. Simulations with PWBA cross sections show characteristic radiation intensity to be a factor of 3 less intense compared to experimental measurements.
Geant4 simulations of silver, tungsten, and gold anode tubes are benchmarked against experimental measurements from commercial X-ray tubes, demonstrating that updated cross sections are necessary for accurate characteristic emission modelling. The DWBA cross section use in Geant4 is further validated through comparison of rhodium anode X-ray tube emission as a function of solid angle against identical simulations. Typical average absolute percentage deviation values of simulated X-ray tube emission compared to experimental measurements range from 3 – 10 %. These results establish Geant4 as a reliable and accurate tool for transmission geometry X-ray tube modelling, with positive implications for instrument design and source characterisation in X-ray based spectroscopy techniques.