Characterization of the neutron flux during production of 18F at a medical cyclotron and evaluation of the incidental neutron spectrum for neutron damage studies.

The fast neutron spectrum was measured in an irradiation position adjacent to two 18F (fluorine-18) production targets at a medical cyclotron. The neutron spectrum was modeled using MCNP6 and experimentally determined using activation foils. A three-group neutron spectrum was determined using an over-determined least squares fitting method. The MCNP6 model results and measurements of the activation foils were used as input to unfold the neutron spectrum using the STAYSL PNNL code. The neutron spectrum adjacent to the 18F production target was evaluated for use in incidental experiments to evaluate neutron-induced radiolysis of polyurethane and radiation hardness testing of electronics. The fast neutron flux near the 18F target between the energies of 0.4 - 16.5 MeV was 1.8 - 3.0x109 n cm-2s-1. The neutron dose rate in polyurethane at the irradiation position was 2.8 cGy s-1- 5.8 cGys-1. The 1 MeV equivalent neutron flux was 2.4x109 n cm-2s-1 - 4.0x109 n cm-2s-1.