Measurement of Neutron Flux Spectrum by Multi-Foil Activation Method at the Central Graphite Cavity of UTR-KINKI

At the central cavity in the internal graphite reflector of the Kinki University Reactor, UTR-KINKI, the flux spectrum of neutrons was measured by two foil activation methods: Firstly, so called sandwich foil method was applied to the measurement of epithermal neutron fluxes at 1.46, 4.94, 18.8 and 337 eV, corresponding to the resonances of In-115, Au-197, W-186 and Mn-55, respectively. Secondly, the neutron spectrum was obtained by unfolding multi-foil activation data using a code named NEUPAC. Both results showed a good agreement with that by the two dimensional diffusion (CITATION) and transport (TWOTRAN) calculations with the SRAC code system. Through the present measurements and analysis, it is found that the neutron spectrum at this central cavity is very close to the 1/E standard field in the energy region from about 1 eV to a few hundreds keV and is superior to other 1/E neutron fields ever proposed. Supplementally, distributions of thermal neutrons and Cd-ratio at the central cavity in UTR-KINKI were experimentally obtained.