MultiTrans, a new radiation transport code

A new deterministic radiation transport code MultiTrans has been developed for three-dimensional neutron transport problems. The solution method is based on efficient tree-multigrid (TMG) technique and SP3 transport approximation. In the multigrid solution technique, the iteration procedure is accelerated by first solving the problem on coarser grid and then transferring data to finer grids, and backwards. In the tree-multigrid technique, adaptive subdivision procedure enables refinement of the calculation grid on material surfaces or by computational demand. The tree-structure enables the modelling of complicated geometries and surfaces accurately with only a limited number of mesh cells. The three-dimensional octree grid is generated directly from stereolitography (STL) files, which can be exported from practically all CAD-systems. The octree grid can also be easily generated from segmented CT/MRI images. This enables the application of the MultiTrans code to BNCT treatment planning. Other applications are in nuclear engineering research and industry. It might also be possible to apply the tree-multigrid technique to coupled electron/photon radiation transport problem of conventional radiotherapy. Thorough testing of the MultiTrans code performance and accuracy will of course be required. As a BNCT benchmark, the neutron fluence rate distribution has been calculated for cylindrical PMMA (polymethyl-methacrylate) phantom, used in characterisation of the Finnish epithermal beam at FiR 1 BNCT facility in Otaniemi. The source plane fluence used in Monte Carlo based treatment planning at the Finnish BNCT facility has been utilised. Calculated Au and Mn reaction rates will be presented, with direct comparison to Au and Mn foil activation measurements performed in the PMMA phantom centreline.