D9.119 - Report summarising the computational developments needed to realise full online dosimetry using simulation of voxel phantoms in the workplace

It was acknowledged at the outset of this project that real time online dosimetry with full Monte Carlo modelling in anthropomorphic phantoms would be too severe a challenge for workplaces where neutrons contribute a significant fraction of the total effective dose. The reasons for this are complex, with the scale of neutron workplaces, the inherently mixed-radiation nature of the fields and the strong scattering experienced by neutrons in the workplace being factors. But there is a fundamental issue with the application of energy dependent radiation weighting factor in the workplace for voxelized phantoms which forces the use of a two-step Monte Carlo process: initial calculation of the energy and direction distribution of the fluence at a point, and then the application of precalculated energy and angle dependent fluence to effective dose conversion coefficients. This is because the radiation weighting factor applies to the energy of the neutron as it enters the body, rather than the energy of the neutron that is depositing the energy: neutrons deposit energy in several interactions but the Monte Carlo code cannot apply a weighting for the absorbed dose deposited based on the energy of the neutron as it entered the body.