Tests of a novel method to assay SNM using polarized photofission and its sensitivity in the presence of shielding

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Accelerators, spectrometers, detectors and associated equipment, 2015-03, Vol.776 (C), p.107-113
• Main Authors: Mueller, J.M., Ahmed, M.W., Kafkarkou, A., Kendellen, D.P., Sikora, M.H., Spraker, M.C., Weller, H.R., Zimmerman, W.R.
• Format: Article
• Language: English
• Subjects: Active interrogation; Assay; Enrichment; Fission; Neutron detectors; Polarized beams
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2014.12.022

A novel method to identify Special Nuclear Material was recently developed (Mueller et al., 2014) [1]. This method relies upon using a linearly polarized γ-ray beam to induce photofission of a sample and then comparing the prompt fission neutron yields in and out of the plane of beam polarization. The present paper will describe experimental tests of this new technique and assess its sensitivity in the presence of shielding. The capability of this technique to measure the enrichment of uranium was tested by using combinations of thin 235U and 238U foils of known enrichments. The sensitivity of this assay to shielding by lead, steel, and polyethylene was experimentally measured and simulated using GEANT4. These tests show that the measured asymmetry can indeed be used to determine the enrichment of materials composed of an admixture of 235U and 238U, and this asymmetry is relatively insensitive to moderate amounts of shielding.