Assuming thermal cross section data: (a) What fuel-to-moderator ratio will yield a k. of 1.25 if the fuel is233U and the moderator is heavy water (D½O)? (b) If the non-leakage

probability for a sphere of radius R is definedby P_{N L}=\frac{1}{1+L^{2} B^{2}} where L? = the diffusion length and B = ()², what is the radius of a sphere of this material that is critical? [Continue to assume mono-energetic neutrons.]