Measurement of the neutron field characteristics inside and outside the vault of a 70 MeV cyclotron

Neutron fields are created inside and outside the vault as byproducts of radioisotope production of the 70 MeV cyclotron at Zevacor Molecular Inc. Neutron energy distribution measurements were obtained for a 10 μΑ accelerator proton beam incident on a Rb/Ga target using the Nested Neutron Spectrometer. The neutron fluence rate at a 30 cm diameter conduit outside of the vault reached 3.95×10⁴ cm⁻² s⁻¹ and was measured to be 7.68×10⁷ cm⁻² s⁻¹ inside the vault at a distance of 1 m from the target. Neutron output is expected to be approximately 20 times greater during routine operational conditions (200 μΑ). Inside the vault, the spectrum showed features similar to theoretical models and may provide a useful environment to test space-bound electronics.