Neutron spectral fluence and dose distribution inside a NYLON 6 phantom irradiated with pencil beam of high energy protons

The calculation of the spatial distribution of the radiation weighting factor for neutrons allowed us to estimate the distribution of the neutron equivalent dose inside the phantom. The maximal value of the neutron equivalent dose within the phantom reached 42, 24, and 15 pSv per one primary 100, 150, and 200 MeV proton, respectively, and occurred on the beam axis roughly at the half of the proton range. With respect to the proton dose, these maximal values of the neutron equivalent dose correspond to 2.1%, 1.3%, and 1.4% of the proton dose in the Bragg peak for these proton energies. Moreover, equivalent doses of secondary induced photons were more than 3 orders of magnitude lower that the neutron ones.