From Fig. 7.7, the total microscopic cross section in iron for neutrons with energy of 27 keV is about 0.4 b. and for a neutron with an energy of 28 keV about 90 b. 

(a) Estimate the fraction of 27-keV neutrons that pass through a 10-cm thick slab without interaction, 

(b) What is this fraction for 28-keV neutrons?

   

Cross section (b) Cross section (b) 103, 10 10 10-11 10 101 10 10-1 10-5 10-10 10-4 10-9 10-3 L 10-8 1 10-2 Neutron energy (MeV) 10-7 10-1 10-6 10 10-5 10 Figure 7.7. Total neutron cross section for iron computed using NJOY-processed ENDF/B (version V) data.