Pulsed-Neutron Diffusion Parameters in Spherical Water Systems

The diffusion parameters of light water have been measured by the pulsed-source method. The neutron bursts were produced from a Texas Neutron Generator by pulsing the ion source and using the ³H (d, n) ⁴He reaction. Neutrons were injected into spherical volumes of H₂O and the decay constants of the neutrons were determined by means of an enriched BF₃ miniature proportional counter. Neutron lifetime measurements were performed on small and large water samples with values of the geometric buckling from 0.035 to 0.655 cm⁻². A harmonic analysis was conducted for the large geometries, while the waiting time method was used for the smaller ones. In the harmonic analysis, it appeared that a detector in a sphere is more sensitive to neutron fluctuation with time than it would be in a rectangular or cylindrical system. The diffusion parameters, D₀ and C, were determined by fitting the decay constants to the equations and , where and are the geometric and the corresponding transport buckling, respectively. The second fit gave a lower standard deviation of C than did the first fit.