Book Description
ABSTRACT: Three-dimensional Monte Carlo coupled electron-photon-positron transport calculations are often performed to determine characteristics such as energy or charge deposition in a wide range of systems exposed to radiation field such as electronic circuitry in a space-environment, tissues exposed to radiotherapy linear accelerator beams, or radiation detectors. Modeling these systems constitute a challenging problem for the available computational methods and resources because they can involve; i) very large attenuation, ii) large number of secondary particles due to the electron-photon-positron cascade, and iii) large and highly forward-peaked scattering. This work presents a new automated variance reduction technique, referred to as ADEIS (Angular adjoint-Driven Electron-photon-positron Importance Sampling), that takes advantage of the capability of deterministic methods to rapidly provide approximate information about the complete phase-space in order to automatically evaluate variance reduction parameters. More specifically, this work focuses on the use of discrete ordinates importance functions to evaluate angular transport and collision biasing parameters, and use them through a modified implementation of the weight-window technique. The application of this new method to complex Monte Carlo simulations has resulted in speedups as high as five orders of magnitude.