Electron field emission Particle-in-Cell (PIC) coupled with MCNPX simulation of a CNT-based flat-panel x-ray source

摘要

A novel x-ray source based on carbon nanotubes (CNTs) field emitters is being developed as an alternative for medical imaging diagnostic technologies. The design is based on an array of millions of micro sized x-ray sources similar to the way pixels are arranged in flat panel displays. The trajectory and focusing characteristics of the field emitted electrons, as well as the x-ray generation characteristics of each one of the proposed micro-sized x-ray tubes are simulated. The electron field emission is simulated using the OOPIC PRO particle-in-cell code. The x-ray generation is analyzed with the MCNPX Monte Carlo code. MCNPX is used to optimize both the bremsstrahlung radiation energy spectra and to verify the angular distribution for 0.25-12 gm thick molybdenum, rhodium and tungsten targets. Also, different extracting, accelerating and focusing voltages, as well as different focusing structures and geometries of the micro cells are simulated using the OOPIC Pro particle-in-cell code. The electron trajectories, beam spot sizes, I-V curves, bremsstrahlung radiation energy spectra, and angular distribution are all analyzed for a given cell. The simulation results show that micro x-ray cells can be used to generate suitable electron currents using CNT field emitters and strike a thin tungsten target to produce an adequate bremsstrahlung spectrum. The shape and trajectory of the electron beam was modified using focusing structures in the microcell. Further modifications to the electron beam are possible and can help design a better x-ray transmission source.