Sensitivity of the simulation of passive neutron emission from UF6 cylinders to the uncertainties in both 19F(α,n) energy spectrum and thick target yield of 234U in UF6

Broughton, David Paul; Croft, Stephen; Romano, Catherine; Favalli, Andrea

doi:10.1016/j.nima.2021.165485

Title: Sensitivity of the simulation of passive neutron emission from UF₆ cylinders to the uncertainties in both ¹⁹F(α,n) energy spectrum and thick target yield of ²³⁴U in UF₆

Journal Article · Mon May 31 00:00:00 EDT 2021 · Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment

DOI:https://doi.org/10.1016/j.nima.2021.165485· OSTI ID:1787295

^[1]; Croft, Stephen ^[2]; Romano, Catherine ^[2];

^[3]

Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Univ. of Texas, Austin, TX (United States)
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Interest in safeguards verification measurements using passive thermal neutron counting to assay ²³⁵U content in large 30B UF₆ canisters has grown in recent years. Here, the prohibitively high cost and impracticality of using reference 30B calibration cylinders extensively will likely make accurate simulations of increasing interest. Accuracy of the simulated response will define the confidence in the predicted response and the extent to which simulations can reasonably be relied upon. With ²³⁴U driven ¹⁹F(α, n) reactions being the main neutron source in low enriched UF₆ the uncertainties of the ¹⁹F(α, n) energy spectrum and the thick target yield of ²³⁴U in UF₆ propagate into the uncertainty in the predicted response and represent a major influence of basic nuclear data. Here sensitivity of the simulated total (Singles) and coincidence (Doubles) count rates are assessed for the Passive Neutron Enrichment Meter using six potential ¹⁹F(α, n) neutron energy spectra over a range of enrichments and material distributions. The results indicate that variations in the Singles and Doubles due to simulated (α, n) neutron spectrum are less than 1.5% for this set of simulated neutron spectra, with dependence varying inversely with enrichment. Singles uncertainty is only slightly less than that of the thick target ¹⁹F(α, n) yield corresponding to the primary neutron source, whereas the ¹⁹F(α, n) yield dependence of the Doubles is reduced by the non-negligible ²³⁸U(SF) coincident neutron emissions. Based on available thick target ¹⁹F(α, n) yield estimates the uncertainty is on the order of 5%, establishing this as the main nuclear data limitation when simulating thermal neutron detectors response for 30B UF₆ storage cylinders. Based on these findings, it appears that the measurement and evaluation of the thick target ¹⁹F(α, n) yield for uranium hexafluoride is due.

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Research Organization:: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

Sponsoring Organization:: USDOE National Nuclear Security Administration (NNSA), Office of Nonproliferation and Verification Research and Development (NA-22); USDOE

Grant/Contract Number:: 89233218CNA000001

OSTI ID:: 1787295

Alternate ID(s):: OSTI ID: 1788092

Report Number(s):: LA-UR-21-20862; TRN: US2210440

Journal Information:: Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 1009; ISSN 0168-9002

Publisher:: ElsevierCopyright Statement

Country of Publication:: United States

Language:: English

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Title: Sensitivity of the simulation of passive neutron emission from UF6 cylinders to the uncertainties in both 19F(α,n) energy spectrum and thick target yield of 234U in UF6

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Title: Sensitivity of the simulation of passive neutron emission from UF₆ cylinders to the uncertainties in both ¹⁹F(α,n) energy spectrum and thick target yield of ²³⁴U in UF₆