Extraction of polychromatic thermal neutrons by Bragg diffraction to use for prompt gamma neutron activation analysis

Byun, S. H.; Choi, H. D.; Jun, B. J.; Kim, M. S.
July 2000
AIP Conference Proceedings;2000, Vol. 529 Issue 1, p731
Academic Journal
Extraction method of thermal neutron beam by Bragg diffraction is investigated. A thermal neutron beam is used for the Prompt Gamma Neutron Activation Analysis system at HANARO, a 30 MW research reactor in the Korea Atomic Energy Research Institute. Polychromatic beam including all orders of diffraction is obtained by setting a pair of pyrolytic graphite crystals with a Bragg angle of 45° on a horizontal white beam line. Diffracted neutron flux at the sample position is calculated by considering the integrated reflectivity and mosaic spread of crystals. Due to the divergence effect, the mosaic spread of crystals is optimized to give the maximum and flat flux at the sample position. An experiment has been performed to verify the reflectivities for high order diffractions from pyrolytic graphite. When the focusing technique of bending the crystals is adopted, a design value of 1.0×10[sup 8] n/cm[sup 2]s is expected at the sample position. Hence Bragg diffraction is a promising method of extracting thermal neutrons for PGNAA. © 2000 American Institute of Physics.


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