Changes to the 252Cf neutron spectrum caused by source encapsulation

Volume: 54, June 2017, pages 44-53,

Authors: R. Weinmann-Smith^1,2, S. Croft³, M.T. Swinhoe¹, A. Enqvist²

¹_{Safeguards Science and Technology Group (NEN-1), Nuclear Nonproliferation Division, Los Alamos National Laboratory,} ²_{Engineering Department, University of Florida,} ³_{Safeguards and Security Technology, Nuclear Security & Isotope Division, Oak Ridge National Laboratory}

Abstract:

Lightly encapsulated 252Cf sources are commonly used to characterize and calibrate neutron detectors for safeguards applications without much attention being paid to what it means for the encapsulation to be neutronically “light”. In this work we quantify the impact of encapsulation on both the neutron spectrum and neutron intensity. We find that a 1.3 mm shell of copper reduces the mean energy by about 1 %. Thus encapsulation can be used to deliberately adjust the mean energy to match, for example, that of the spontaneously fissile Pu nuclides. The spectrum cannot be matched perfectly however and so the influence of encapsulation on a particular system calibration is case specific. We demonstrate using encapsulation to match the Pu neutron detection efficiency for a common safeguards detector, the Active Well Coincidence Counter.

Keywords: NDA; Monte Carlo; Prompt Fission Neutron Spectrum, 252Cf, encapsulation

Reference guideline:

Weinmann-Smith, R., Croft, S., Swinhoe, M.T., & Enqvist, A. (2017). Changes to the 252Cf neutron spectrum caused by source encapsulation. ESARDA Bulletin - The International Journal of Nuclear Safeguards and Non-proliferation, 54, 44-53. https://doi.org/10.3011/ESARDA.IJNSNP.2017.6