At the Kyoto University Critical Assembly, a series of reactor physics experiments on the accelerator-driven system (ADS) coupled with the fixed-field alternating gradient (FFAG) accelerator are carried out, and the spallation neutrons generated by 100-MeV protons from the FFAG accelerator are successfully injected into the cores. In the ADS experiments, the neutron characteristics of the solid target are investigated through static and kinetic analyses, when the external neutron source of the neutron spectrum (the W, W-Be, or Pb-Bi target) is varied. The results demonstrate that the neutron yield is large with the W target, but a discrepancy is observed between the experiments and the calculations, because the experimental uncertainty of proton monitoring is attributable to defocusing of proton beams. With the use of reaction rate distribution in the core region, the static parameters are estimated fairly well in the analyses of the neutron multiplication and subcritical multiplication factor. In the kinetic experiments, the variation of the solid target used is clearly evident in the prompt neutron decay constant and the subcriticality.
