Absolute Reaction Rate Measurement With D-D Neutron Source in Polyethylene Spherical Shell

The absolute reaction rate distribution measurements in a polyethylene spherical shell with 38.6 cm outside diameter and 10 cm thickness were performed with D-D neutron source. By combining fission method and activation method, rich-uranium fission chamber, depleted-uranium fission chamber, ²³⁷Np fission chamber and ¹¹⁵In activation foils were placed at several positions on the equatorial line of the inner face of the shell, and the absolute reaction rates were obtained. The uncertainty of fission rates is 2.5%-4.3%, while the uncertainty of activation rates is about 6.3%. The reaction rates were calculated by MCNP and ENDF/B-Ⅶ.0. The calculated results are lower than the measured results and ²³⁸U is typical.