Objects of various shapes, with some appreciable hydrogen content, were exposed to fast neutrons from a pulsed: D-T generator, resulting in a partially-moderated spectrum of backscattered neutrons. The thermal component of the backscatter was used to form images of the objects by means of a coded aperture thermal neutron imaging system. Timing signals; from the neutron generator were used to gate the detection system so as to record only events consistent with thermal neutrons traveling the distance between the target and the detector. It was shown that this time-of-flight method provided a, significant improvement in image contrast compared to counting all events detected by the position-sensitive 3Hr: proportional chamber used in the imager. The technique may have application in the detection and shape-determination 0.f land mines, particularly non-metallic types.

No abstract