Characterization of neutron leakage field coming from 18O(p,n)18F reaction in PET production cyclotron

This paper shows a new merthod for characterization of the secondary neutron field quantities, specifically neutron spectrum leaking from 18O enriched H2O XL cylindrical target in IBA Cyclone 18/9 in the energy range of 1-15 MeV. Spectrum is measured by stilbene scintillation detector in different places. The neutron spectra are evaluated from the measured proton recoil spectra using deconvolution through maximum likelihood estimation. A leakage neutron field is an interesting option for irradiation experiments due to quite high flux, but also to the validation of high energy threshold reactions due to relatively high average energy. Measured neutron spectra are compared with calculations in MCNP6 model using TENDL-2017, FENDL-3, and default MCNP6 model calculations. TENDL-2017 and FENDL-3 libraries results differ significantly in the shape of the neutron spectrum for energies above 10 MeV while MCNP6 gives incorrect angular distributions. Activation measurements of different neutron induced reactions support characterization. The 18F production yield is in a good agreement with TENDL-2017 proton library calculation within respective uncertainties.