The impact of gate width setting and gate utilization factors on plutonium assay in passive correlated neutron counting

Abstract

a b s t r a c tIn the field of nuclear safeguards, passive neutron multiplicity counting (PNMC) is a method typically employed in non-destructive assay (NDA) of special nuclear material (SNM) for nonproliferation, verification and accountability purposes. PNMC is generally performed using a well-type thermal neutron counter and relies on the detection of correlated pairs or higher order multiplets of neutrons emitted by an assayed item. To assay SNM, a set of parameters for a given well-counter is required to link the measured multiplicity rates to the assayed item properties. Detection efficiency, die-away time, gate utilization factors (tightly connected to die-away time) as well as optimum gate width setting are among the key parameters. These parameters along with the underlying model assumptions directly affect the accuracy of the SNM assay. In this paper we examine the role of gate utilization factors and the single exponential die-away time assumption and their impact on the measurements for a range of plutonium materials. In addition, we examine the importance of item-optimized coincidence gate width setting as opposed to using a universal gate width value. Finally, the traditional PNMC based on multiplicity shift register electronics is extended to Feynman-type analysis and application of this approach to Pu mass assay is demonstrated.

Sorting fission from parasitic coincidences of neutrons and gamma rays in plastic scintillators using particle times of flight

“…The count rates of singles (S, sum of all the triggers), doubles (D, which is S times the difference between the mean values of (R+A) and (A) registers of M1) and triples (T, which is a complex deconvolution of (R+A) and (A) distributions with the registers M2, M3, M4, etc.) are calculated following the equations detailed in [23][24][25]. As follows from (2-4), the signalto-noise ratio (SNR) increases significantly from singles to triples because M1 (two fired detectors) is dominated by correlated γn pairs of AmBe and γγ pairs of 60 Co, whereas higher-order multiplicities (M2, M3, etc.)…”