Neutron beam design for low-intensity neutron and gamma-ray radioscopy using small neutron sources

Two small neutron sources of ²⁵²Cf and ²⁴¹Am-Be radioisotopes were used for design of neutron beams applicable to low-intensity neutron and gamma-ray radioscopy (LINGR). In the design, Monte Carlo code (MCNP) was employed to generate neutron and gamma-ray beams suited to LINGR. With a view to variable neutron spectrum and neutron intensity, various arrangements were first examined, and neutron-filter, gamma-ray shield, and beam collimator were verified. Monte Carlo calculations indicated that with a suitable filter-shield-collimator arrangement, thermal neutron beam of 3900 ncm^-2s^-1 with neutron/gamma ratio of 7 × 10⁷, and 25 ncm^-2s^-1 with very large neutron/gamma ratio, respectively, could be produced by using a ²⁵²Cf (122 μg) and a ²⁴¹Am-Be (37 GBq) radioisotopes at the irradiation port of 35 cm from the neutron sources.