Ferrite steel is often used as the material for a reactor pressure vessel. After 40 years of service, it was found that Cu-rich clusters or precipitates are generated in the alloy. These precipitates can act as pinning points for mobile dislocations. The density of the precipitates is 1×10^15 cm^-3 and the average precipitate diameter is 5 nm. What is the average spacing between these clusters in a plane where dislocations are moving? If the shear modulus of the steel is 90 GPa, and the magnitude of the Burgers vector of the mobile dislocation in the steel is 0.3 nm, calculate the increase in yield stress (in MPa) caused by the radiation-induced Cu precipitates. Assume there are two kinds of BCC Fe alloys, A and B, with very similar strain-stress curves before irradiation. Alloy A has a larger grain size (e.g., 100 micrometers) and alloy B has a smaller grain size (e.g., 0.1 micrometer). Which alloy will exhibit a larger radiation-induced hardening after receiving the same amount of radiation damage (e.g., 0.5 dpa)? Provide a brief explanation for your answer.