Application of automated weight windows to spallation neutron source shielding calculations using Geant4

We present an implementation of a general weight window generator for global variance reduction in Geant4 based applications. The implementation is flexible and can be easily adjusted to a user-defined model. In this work, the weight-window generator was applied to calculations based on an instrument shielding model of the European Spallation Source, which is currently under construction in Lund, Sweden. The results and performance of the implemented methods were evaluated through the definition of two figures of merit. It was found that the biased simulations showed an overall improvement in performance compared to the unbiased simulations. The present work demonstrates both the suitability of the generator method and Geant4 for these types of calculations. (C) 2015 Elsevier By. All rights reserved. (Less)