Time-correlated pulse-height measurements of low-multiplying nuclear materials

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Vol. 729; pp. 108 - 116
• Main Authors: Miller, E.C., Dolan, J.L., Clarke, S.D., Pozzi, S.A., Tomanin, A., Peerani, P., Marleau, P., Mattingly, J.K.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 21.11.2013
• Subjects: Accelerators; Benchmarking; Disks; Estimates; Integrals; Liquid scintillators; MCNPX-PoliMi; MOX; Multiplication; Neutron–gamma correlation; Simulation; Sub-critical multiplication; Sub-critical multiplication; Neutron–gamma correlation; MCNPX-PoliMi; Liquid scintillators
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2013.06.062

Methods for the determination of the subcritical neutron multiplication of nuclear materials are of interest in the field of nuclear nonproliferation and safeguards. A series of measurements were performed at the Joint Research Center facility in Ispra, Italy to investigate the possibility of using a time-correlated pulse-height (TCPH) analysis to estimate the sub-critical multiplication of nuclear material. The objective of the measurements was to evaluate the effectiveness of this technique, and to benchmark the simulation capabilities of MCNPX-PoliMi/MPPost. In this campaign, two low-multiplication samples were measured: a 1-kg mixed oxide (MOX) powder sample and several low-mass plutonium–gallium (PuGa) disks. The measured results demonstrated that the sensitivity of the TCPH technique could not clearly distinguish samples with very-low levels of multiplication. However, the simulated TCPH distributions agree well with the measured data, within 12% for all cases, validating the simulation capabilities of MCNPX-PoliMi/MPPost. To investigate the potential of the TCPH method for identifying high-multiplication samples, the validated MCNPX-PoliMi/MPPost codes were used to simulate sources of higher multiplications. Lastly, a characterization metric, the cumulative region integral (CRI), was introduced to estimate the level of multiplication in a source. However, this response was shown to be insensitive over the range of multiplications of interest. •Present results of measurements of MOX fuel and PuGa disks.•Compared measurement results to simulations performed using MCNPX-Polimi and MPPost.•Investigated using correlated γ–n pairs to determine the multiplication of a system.