Spectrum Measurement of Neutrons and Gamma-rays from Thick (H2O)-O-18 Target Bombarded with 18 MeV Protons

Nuclear data on proton-induced neutron and gamma-ray production in the energy range from 10 to 20 MeV is important to estimate the shield design and activation of low-energy cyclotron facilities for medical use such as production of radiopharmaceuticals in positron emission tomography (PET). We have measured double-differential thick target yields (TTYs) of neutrons and gamma-rays from a O-18-enriched water ((H2O)-O-18) target induced by 18 MeV protons in order to estimate leakage radiations from a cyclotron and the neutron-induced activation in the production process of the F-18-tagged fluorodeoxyglucose (FDG) which is a common radiopharmaceuticals for PET. Neutrons and gamma-rays were measured with 5.08 cm-diameter x 5.08 cm-long NE213 scintillators for eight laboratory angles between 15- and 150-degrees. After applying a neutron-gamma-ray event separation using the pulse-shape-discrimination (PSD) technique the neutron and gamma-ray events were analyzed by a time-of-flight (TOF) technique and an unfolding technique, respectively. The measured TTYs were compared with TENDL-2009 data library and the physical model calculations with MCNPX and PHITS. The calculated TTYs roughly agree with the measured data.