4) As depicted in the figure below, a 100 MBq "Co point source is located 20 cm from a person (P point, assume water), with a 2.5 cm, poor-geometry aluminum shield between the source (S) and person (P). Only photons with radiation yields (Y) larger than 80% are considered here (the decay scheme of > Co is attached): (a) Calculate the gamma-ray flux at point P in 'em2. sec ") and (b) Calculate the gamma-ray dose in Gy at point P (assume water) for 24 hours. For this problem: (1) use buildup factor, (2) DO NOT calculate the dose using exposure or gamma-ray constant, so you should use the direct dose calculation method, and (3) ignore attenuateon in air. (20 points). Al P 57 Co O A = 100 MBq 2.5 cm 20 cm