We have designed and characterized a cyclotron-driven neutron source based on the 13 MeV proton beam for thermal-neutron imaging systems. Accelerator-based neutron sources mainly comprise \romannumeral 1) a target emitting neutrons via nuclear reactions with high energy protons, \romannumeral 2) moderators reducing the kinetic energy of the fast neutrons to allow neutron radiography and \romannumeral 3) reflectors optimizing the divergence of the neutron beam. In this study, a conceptual design consisting of a 1.25 mm-thick beryllium target, a 3 cm-thick HDPE (high-density polyethylene) moderator and a 50 cm-cube-shaped graphite reflector has been proposed. For realistic demonstrations, not only have we calculated the neutron fluences and distributions at up to L/D = 200, where L is the aperture-to-detector distance and D is the aperture diameter, which is an important factor in the field of radiography, but also we have confirmed that the neutron flux of up to $1.4\times10^{5}$ n/cm$^{2}\cdot$s can be obtained when the source-to-detector distance is 3 m.

Keywords: Neutron Source, Cyclotron, Monte Carlo Simulation, \textsc{Geant4}, Target, Moderator, Neutron Radiography