title: Efficient x-ray tube simulations.
abstract: This article describes an efficiency study of directional bremsstrahlung splitting (DBS) for x-ray tube modeling. DBS is shown to be up to five or six orders of magnitude more efficient at 50 or 135 kV tube potential than a simulation without splitting, and 60 times more efficient compared to uniform bremsstrahlung splitting. A methodology is presented to determine the optimum splitting number for a given situation using a second degree polynomial expression derived from theoretical considerations. Very large optimum splitting numbers are found for small fields (5 mm radius) at 1 m from the x-ray source, which are relevant for half-value layer (HVL) calculations and for simulations related to primary air kerma standards. Two approaches for the calculation of kerma at a plane and inside a volume using track-length estimation are implemented in BEAMnrc, a user-code from the EGSnrc Monte Carlo simulation system for photon and electron transport. A practical application of DBS to HVL calculations for a Comet MXR-320 x-ray tube is reported. The agreement with measured HVLs at different constant tube potentials is found to be better than 2.3%.
authors.affiliation: Ionizing Radiation Standards, National Research Council of Canada, Ottawa K1A 0R6, Canada. mainegra@irs.phy.nrc.ca
authors.forename: Ernesto
authors.initials: E
authors.lastname: Mainegra-Hing
authors.forename: Iwan
authors.initials: I
authors.lastname: Kawrakow
mesh_terms: D003198:Computer Simulation; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D015233:Models, Statistical; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods; D012542:Scattering, Radiation; D014965:X-Rays