Neutron fluence rate measurements in a PGNAA 208-liter drum assay system using silicon carbide detectors

• Published in: Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms Beam interactions with materials and atoms, 2004, Vol.213, p.400-405
• Main Authors: Dulloo, A.R., Ruddy, F.H., Seidel, J.G., Lee, S., Petrović, B., McIlwain, M.E.
• Format: Article
• Language: English
• Subjects: Neutron detection; Nondestructive assay; PGNAA; Silicon carbide
• ISSN: 0168-583X; 1872-9584
• DOI: 10.1016/S0168-583X(03)01662-8

Pulsed prompt gamma neutron activation analysis (PGNAA) is being implemented for the nondestructive assay (NDA) of mercury, cadmium and lead in containers of radioactive waste. A PGNAA prototype system capable of assaying 208-liter (55-gallon) drums has already been built and demonstrated. As part of the evaluation of this system, the thermal neutron fluence rate distribution in a drum containing a combustible waste surrogate was measured during PGNAA runs using a silicon carbide neutron detector. The fast charge-collection time of this detector type enabled the investigation of the neutron kinetics at various locations within the matrix during and between pulses of the system’s 14-MeV neutron source. As expected, the response of a SiC detector equipped with a lithium-6 fluoride layer is dominated by thermal neutron-induced events between pulses. The measurement results showed that the thermal neutron fluence rate is relatively uniform over a radial depth of several centimeters in the matrix region that contributes a significant fraction of the prompt gamma radiation incident on the system’s photon detector.