REAL AND VIRTUAL SAMPLING IN VARIATIONAL PROCESSING OF STOCHASTIC SIMULATION IN NEUTRON-TRANSPORT - THE ONE-DIMENSIONAL ROD

We are seeking to combine conventional analogue Monte Carlo simulation that might be used in realistic three-dimensional problems, with vari ational processing to reduce variance and improve the ratio of accurac y to computing costs. At this stage we investigate a one-dimensional t ransport problem with left and right scattering, for which exact solut ions are available for comparison. We can show that the usual Monte Ca rlo simulation can be used not only to estimate the forward flux but a lso the importance or adjoint flux of neutrons sampled, where the impo rtance is to be used in the variational processing. Hence the single s imulation potentially holds information to improve the accuracy. The e fficiency is improved by the use of virtual rather than fictitious sam pling. Virtual sampling is introduced, which consists of marking every location of a neutron as a virtual source, and found to be more effic ient than fictitious sampling to determine the importances. (C) 1998 E lsevier Science Ltd. All rights reserved.