a 1 mci source of 60co is placed in the center of a cylindrical water-filled tank with an inside diameter of 20 cm and depth of 100 cm. the tank is made of iron with a wall thickness of 1 cm. what is the uncollided flux density at the outer surface of the tank nearest the source? you will need data from appendix d of the course text. making the right assumption(s) simplifies the calculation.