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Some issues of Superman have indicated the mechanism by which green kryptonite may hurt Superman. Like Hanna-Barbera's Birdman, Superman in some ways is a living solar battery; his cells absorb electromagnetic radiation from stars (like Earth's sun). Kryptonite's radioactivity possibly interferes with this process, driving the energy out of his cells in a painful fashion. Long term and high-level exposure to green kryptonite can be fatal to Superman. In post-Crisis comics, long-term exposure to kryptonite is known to have the same effects on human beings as exposure to Earth-born radioactive materials; these effects include cancer. Lex Luthor discovered this inadvertently after acquiring a ring with a green kryptonite fragment set in it to provide protection against Superman—Luthor first lost the hand he wore the ring on to cancer and later had to have his brain transferred into a new, cloned body after the cancer was found to have spread throughout his original body.