Enhancement of thermal neutron self-shielding in materials surrounded by reflectors

Chilian, Cornelia; Kennedy, Gregory
July 2012
Journal of Radioanalytical & Nuclear Chemistry;Jul2012, Vol. 293 Issue 1, p179
Academic Journal
Materials containing from 41 to 1124 mg chlorine and surrounded by polyethylene containers of various thicknesses, from 0.01 to 5.6 mm, were irradiated in a research reactor neutron spectrum and the Cl activity produced was measured as a function of polyethylene reflector thickness. For the material containing the higher amount of chlorine, the Cl specific activity decreased with increasing reflector thickness, indicating increased neutron self-shielding. It was found that the amount of neutron self-shielding increased by as much as 52% with increasing reflector thickness. This is explained by neutrons which have exited the material subsequently reflecting back into it and thus increasing the total mean path length in the material. All physical and empirical models currently used to predict neutron self-shielding have ignored this effect and need to be modified. A method is given for measuring the adjustable parameter of a self-shielding model for a particular sample size and combination of neutron reflectors.


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