Electron Shielding

You are a radiation scientist working for the space agency. A Mission Coordinator asks you to design shielding to prevent monoenergetic 10 MeV electrons from interacting with a cell culture that is to be flown on an upcoming space shuttle mission. The cell culture is covered with a 1 cm thick sheet of Lucite (density = 1.19 g/cm^3) - see figure below.

a) What thickness of lead (in cm) is required on top of the Lucite to prevent the 10 MeV electrons from reaching the culture?

b) The Mission Coordinator assumes that when the electrons are shielded out, that there will be no other radiation sources interacting with the cell culture. Assuming that your spacecraft is shielded from all other external radiations, and that we consider natural radiation from the materials and personnel surrounding the culture to be inconsequential, is she correct in her assumption?

c) What would be the effect, if any, on the radiation field around the cell culture if the positions of the lead and the Lucite were swapped?


(Question is also included in attachment)