A Human Voxel Phantom Distributed Source Monte Carlo Solution
Congress title :ANS/ENS International Winter Meeting and Nuclear Technology Expo
Congress location :Washington
Congress date :11/11/2007
Distributed source Monte Carlo radiation transport calculations are very challenging. The Monte Carlo method is well-suited for isolated source problems, but for distributed source problems an adjoint solution is usually préférable. Unfortunately, there is no widely-used continuous-energy adjoint Monte Carlo solver available. Multigroup Monte Carlo adjoint solvers are available, but thèse lack the accuracy and detector modeling capabilities of continuous-energy Monte Carlo.
Our motivation is an anthropomorphic voxel phantom which represents a maie body with radioactive contamination (photon sources) in the major organs .This model is used to simulate the spectrometric measurement of activity retained in organs after internai contamination with radionuclides. It is represented in MCNP / MCNPX by a 156 x 72 x 487 lattice of voxel éléments. For the lung measurement, four germanium detectors are located above the chest, each with 16384 energy déposition puise channels. Thèse detectors are modeled with a "pulse-height" tally in MCNP/MCNPX. Presently only MCNPX allows variance réduction with pulse-height tallies, and DXTRAN, the obvious variance réduction choice, is not allowed with pulse-height tallies.
Our Monte Carlo solution features several novel modeling innovations and new code developments. These are:
• a source rejection sampling scheme to sample
différent organs without having to provide a distribution to each individual voxel point;
• a new source angle biasing capability developed specifically for this model with applicability to many other distributed source problems;
weight Windows generated in an unconventional manner.