Is there any way to reflect gamma rays?
Since they have the shortest wavelength of all EM radiation, gamma rays are extremely deeply penetrating. Gamma ray mirrors do exist, but they are usually in the form of multilayer reflectors; sheets of reflecting material spaced by layers of gamma-transparent material. As a gamma ray passes down into the reflector, a succession partial reflections occur, one at each layer of reflecting material. A multilayer reflector is usually several metres thick, perhaps more, depending on the energy of the rays it works with. Multilayer reflectors of this nature are much more effective at shallow, grazing angles. For a gamma ray approaching it at a higher angle, less energy will be reflected. There are no theoretical limits to the efficiency of gamma ray mirrors, only engineering and economical concerns. The best attainable efficiency in practice probably peaks somewhere around 80% to 90%. You could probably shield against the remaining 10% to 20% using lead or depleted uranium, which absorbs the
