Development and Validation of a Geant4 Monte Carlo Model for Excillum’s NanoTube Transmission X-Ray Source

Accurate modeling of spot size and beam characteristics in X-ray sources is crucial for opti-mizing design and ensuring high performance. The study investigated the use of the Monte-Carlo simulation toolkit Geant4 for simulating the NanoTube, one of Excillum’s transmis-sion X-ray tubes, and validating the simulations by comparing simulated and experimentallymeasured X-ray spots. Simulated and measured spot shapes agreed well with only small dis-crepancies and an optimization of the target thickness was done to find a thickness whichminimizes the tails and full width half maximum of the spot. The computational efficiencyof the software was compared with another Monte-Carlo code, PENELOPE, already in useby the company, and it was found that Geant4 had around one magnitude higher efficiencyusing the current setup. Further improvements can be done to achieve faster simulationsby incorporating more efficient variance reduction techniques, optimizing step sizes as wellas the possibility of accelerating simulations with GPUs. These findings demonstrate thatGeant4 can both reproduce the NanoTube’s spot geometry and shorten simulation time,enabling more rapid design iterations for next-generation transmission tubes.