The Expanding Role of the Small Van De Graaff in Nuclear Nondestructive Analysis

In support of Nuclear Safeguards, a 3-MeV Van de Graaff accelerator was installed at LASL to aid research in techniques for nondestructive assay of fissionable materials. Monoenergetic neutrons make possible fissile assay techniques less influenced by self-absorption than thermal interrogation and more discriminating of fissile over fertile material than use of partially moderated high-energy neutrons. Delayed fission-neutron counting, a valuable assay technique, is facilitated by pulsed neutron on-to-off ratios in excess of 109, achieved with special beam-handling techniques. Where high neutron backgrounds, e.g. from samples containing 240Pu, preclude delayed-neutron counting, fission prompt-neutron counting with an energy-biasable detector is applied. The increasing facility workload, which includes detector development and calibration, research in trace analysis by proton-induced x-ray fluorescence and research in light-element isotopic assay by means of charged-particle induced reactions, indicates that technological application may more than supplant dwindling nuclear research as a market for accelerators of this class.