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Improved Bonner sphere neutron spectrometry measurements for the nuclear industry

Roberts, N J; Thomas, D J; Visser, T P P (2017) Improved Bonner sphere neutron spectrometry measurements for the nuclear industry. Radiation Physics and Chemistry, 140. pp. 319-321.

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Abstract

A novel, two-stage approach has been developed for producing the a priori spectrum where neutrons are produced by spontaneous fission and (alpha,n) reactions, e.g. in UF6. The code SOURCES 4C is first used to obtain the energy spectrum of the neutrons inside the material, which is then fed into a MCNP model of the entire geometry to derive the neutron spectrum at the location of the Bonner sphere. Using this as the a priori spectrum produces a much more detailed unfolded Bonner sphere spectrum retaining fine structure from the calculation that would not be present if a simple estimated spectrum had been used. This is illustrated using a Bonner sphere measurement of the neutron energy spectrum produced by a 48Y cylinder of UF6. From the unfolded spectrum an estimate has been made of the neutron ambient dose equivalent, i.e. the quantity which a neutron survey instrument should measure. The difference in the ambient dose equivalent of the unfolded spectrum is over 10% when using the novel approach instead of using a simpler estimate consisting of a single high energy peak, 1/E continuum, and thermal peak.

Item Type: Article
Keywords: Bonner spheres, neutron spectrometry, UF6, Monte Carlo, unfolding, neutron survey instruments
Subjects: Ionising Radiation > Neutron Metrology
Divisions: Chemical, Medical & Environmental Science
Identification number/DOI: 10.1016/j.radphyschem.2017.02.019
Last Modified: 13 Feb 2018 11:22
URI: http://eprintspublications.npl.co.uk/id/eprint/7701

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