A cost effective, highly sensitive, passive neutron fluence monitor for nuclear contraband detection

Natural gadolinium possesses a very high thermal neutron capture (n, γ) cross-section on the other hand, carbon-doped aluminium oxide thermoluminescence dosimeters (α-Al2O3:C), available as TLD 500 are extremely responsive to gamma rays. Hence, by combining those two unique phenomena we have developed a highly sensitive passive neutron detector. The lowest detectable (fission) neutron fluence rate was evaluated to be 7.1 neutrons cm-2 s-1 for an integration period of 1 h. This detection level is adequate enough to detect 3 g of 240Pu from a distance of 1 m, producing spontaneous fission neutrons. Application of this neutron fluence monitor in the passive detection of nuclear contraband is suggested. Further developmental work aiming to augment the present device with instantaneous data display and alarm actuation capabilities is ongoing.