A spacecraft is powered by electricity generated by the heat produced when 23894Pu decays with a half-life of 87.75 y. Engineers predict that the spacecraft will have insufficient power to operate its instruments when the amount of 238 94Pu in its power generators drops below 67 % of the amount it had at launch on September 1, 1977 Required:
In what year will its instruments cease to function?

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia