The Convention on the Physical Protection of Nuclear Materials Implementation Act of 1982, Pub.L. No. 97-351, makes it a criminal offense: (1) to possess unlawfully or use nuclear material when it will cause substantial injury; (2) to take or use nuclear material without authorization, or to obtain nuclear material fraudulently; or (3) to threaten or attempt to use nuclear material for illegal purposes. See 18 U.S.C. § 831.