Experimental evaluation of epithermal neutron self-shielding for 96Zr and 98Mo
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In a previous work we experimentally tested some neutron self-shielding calculations methods for thermal absorbers, from which the semi-empirical “sigmoid method” gave the most accurate results. In this work we aim at evaluating the accuracy of this method on the epithermal self-shielding phenomena as compared to the analytical “MatSSF method”. Metallic foils of Zr and Mo were compactly stacked together into small cylinders (or disks) of different thickness, allowing for up to 20 % epithermal self-shielding when irradiated on two channels of the BR1 reactor. A 2 % relative difference between calculated and experimental self-shielding factors was obtained from the MatSSF method when a perpendicular source-sample axial configuration was assumed, while the isotropic or the co-axial configuration alternatives gave up to 10 % relative differences. On the other hand, the sigmoid method gave relative differences of up to 6 % that can be reduced to just 2 % by applying the “effective” epithermal absorption cross-sections for 98Mo and 96Zr proposed in this work.
KeywordsNeutron self-shielding Resonances Neutron absorption Bell factor Effective epithermal absorption cross-sections Sigmoid method MatSSF method
JEL classificationC20 C30 C60 C61 C63 C90
This work would have not been possible without the technical support from the reactor staff: I. Verwimp, B. Van Houdt, P. Vandycke, S. Van Bijlen and J. Leeuws and their skillful assistance during the irradiations.
- 2.IAEA (2009) MATSSF Program. Vienna. http://www-nds.iaea.org/naa/matssf/. Accessed 10 Aug 2010