At the time to, 5 hours after the detonation of a nuclear warhead, the fission products are distributed as fallout uniformly over a certain area at a density

of 6.2 x 10-5 Ci/cm? A man enters a fallout shelter (shown in Fig. 10.28) at this time and remains there for ts hours.

(a) Show that if his total exposure is not to exceed XR, then his initial exposure rate in the shelter must not exceed as shown formula in figure.

(b) How thick must the concrete roof of the shelter be for the man to receive an expo- sure of 2R over 2 weeks? (Note: For simplicity, take the roof to be

infinite in extent and assume the y-rays have an energy of 0.7 MeV.]