A New Direction Biasing Approach for Monte Carlo Simulation

A new direction biasing approach to a target point and to finite detectors for Monte Carlo simulation is developed, presented, and tested. It properly accounts for the weight adjustments that must be made for the combined choice of a particular scattering (polar) and rotational (azimuthal) angle to obtain a given biasing angle about either a target point or a finite detector. Sample Monte Carlo simulations for a neutron transport problem with isotropic center-of-mass scattering and a gamma-ray transport problem with Klein-Nishina scattering have been done by both the analog and new direction biasing methods. The results indicate that the direction biasing approach is valid and will be very efficient for deep-penetration problems of these two types.