Estimation of neutron production yields from H218O as the 18F-production target bombarded by 18-MeV protons

Abstract

Low-energy medical cyclotrons with energy below 20 MeV are widely used to produce short-lived radionuclides for Positron Emission Tomography (PET). One of the main reactions in these cyclotrons is 18O(p,n)18F by bombarding 18O-enriched water target with 18-MeV protons. The produced secondary neutrons activate the cyclotron components as well as the concrete walls, causing radiological hazards during the maintenance period or decommissioning stage. It is important to have the tools to estimate the mentioned neutron production and to validate the calculations against the available experimental data. In this work, the PHITS-3.02, FLUKA 2011.2x and MCNPX-2.7.0 Monte Carlo codes were used to estimate the neutron yields from proton-induced reactions on H218O target. The TENDL-2017 nuclear data library as well as physics models were used in the PHITS and MCNPX codes for protons and the neutron production yields were compared with the experimental data. It was concluded that by using TENDL-2017+GEM in PHITS-3.02 and by applying either TENDL-2017+Dresner or CEM03+Dresner in MCNPX-2.7.0, the calculated neutron yields and measured data were in good agreement, particularly, in the forward direction. The FLUKA code showed better agreement at backward angles than in the forward direction. The study showed that not only the 18O(p,n)18F reaction produce considerable neutrons, but also other reaction channels contribute to the neutron production significantly. But there are no experimental data available for those channels such as reactions leading to 17O and 14N. Data are needed for more reliable secondary neutron production estimation.