Being so small, they could even be smaller than the wavelength of the electromagnetic radiation, and thus be immune from it. Failing that, a mesh of conducting metal with holes smaller than the wavelength of the radiation, would protect them. The mesh would probably stop it from cloning into the area around, unless it just burst open with dozens of clones when the pressure gets too high inside (and the clones themselves would also have the shielding and would continue the cycle). But this is seriously getting impossible now...