[7] An isotropic point source emits 1010 Y-rays/sec with an energy of 1 MeV. The source is surrounded by a lead shield 10 cm thick. Calculate at the surface of the shield: a) The flux in the absence of the shield; b) The un-collided flux; c) The buildup flux; d) in the absence of the shield; e) without the buildup of scattered radiation; f) with buildup.