5. (20) A LWR has a small gap between fuel pellet and the cladding. While typically filled with He, mistakes were made and ours is filled with air. a) Assuming the composition of air is just nitrogen with a weight fraction of 0.765 and oxygen as the balance and the density of air 1.2103g/cm3. What are the number densities of oxygen and nitrogen atoms? b) Using the information below and information from the chart of the nuclides, estimate the macroscopic scattering cross section and mean free path of thermal neutrons in air. c) Compare this to the macroscopic cross section of air calculated with the 4R2 approximation for hard sphere collisions