Neutron thermalization in graphite

The neutron thermalization and diffusion parameters in graphite were determined by pulsed technique for the neutron flux and the neutron density spectra, respectively. Measurements were performed on assemblies of geometrical bucklings between 2.26×10−3/cm2 and 15.58 × 10−3/cm2, in which, by suitable arrangement of the neutron source and detector, the higher modes of spatial harmonics were diminished. The results indicated that it was necessary to wait 1.5∼2 msec after the injection of 14 MeV neutrons, in order to let the neutron spectrum attain its asymptotic form, independent of assembly size. The thermalization and diffusion parameters for both neutron flux and neutron density spectra were in good agreement with theoretical values.