The gold around satellites are actually very thin layers of mylar, aluminum foil and kapton (a type of golden, transparent plastic) which are used to keep heat inside the satellite inside, and heat outside, outside (See Multi-Layer Insulation). Radiation shielding usually comes from the aluminum structural elements of the spacecraft, or is close to the electronics so you do not waste too much mass on shielding material. Basically, shielding efficacy is most determined by its thickness, so it quickly becomes quite heavy.