Characterization of proton-induced neutron spectrum on Ti-nat target in 11 MeV cyclotron using a passive single moderator neutron spectrometer

The neutron spectrum resulting from the interaction of protons with the materials in the cyclotron must be characterized to predict the effects of neutron activation on the various cyclotron component materials. Neutron spectrum measurements were carried out using a single moderator neutron spectrometer (SCNS) with an Au activation foil detector to analyze proton-induced effects on a natural titanium target in a self-shielding 11 MeV cyclotron. During the experiment, a disk-shaped Ti-nat target, 5 mm in diameter and 1 mm thick, was irradiated with proton beam at a current of 15 μA for 5 min. The neutron spectrometer, located inside the self-shielding, was then used to measure the ¹⁹⁸Au activity of each Au foil employing an HPGe detector of gamma spectrometer. The neutron spectrum was determined using UMG software based on the ¹⁹⁸Au activity values measured from each foil and the calculated response values for each foil detector. The obtained neutron spectrum showed a maximum energy of 8.5 MeV and a peak fast neutron energy of 2.5 MeV, with a total flux of (5.72 ± 0.40) × 10⁵ n/cm²·s, consisting of 75% fast neutrons, 20% epithermal neutrons, and 5% thermal neutrons. The results of measuring the neutron spectrum using SCNS–Au are quite accurate because they only have a 10% difference compared to the simulation results using PHITS software.