Calculation of fast neutron dose in plastic-coated optical fibres

The dose of fast neutrons in optical fibres with hydrogen-containing coating materials is considerably increased by energetic recoil protons. Their contribution to the dose in a SiO2 fibre core is calculated by the Monte Carlo method for different fibre geometries and a fibre optic cable. With 14 MeV neutrons the dose in a single fibre is increased by about 21 %, whereas in fibre bundles the dose increase can reach about 170 %. Maximum dose enhancement in fibre bundles (about 610 %) occurs at neutron energies around 5.5 MeV. The dose increase caused by 14 MeV neutrons in the fibre of a typical laboratory cable is about 124 %.