With the second Nuclear Security Summit fast approaching, it is a good moment to reflect on one of the new issues with which the Seoul summit will attempt to grapple: radiological security. The first Nuclear Security Summit in Washington focused on weapons-usable nuclear materials -- highly enriched uranium and plutonium. The rationale behind a strictly defined agenda was to attract attention to the materials that pose the gravest dangers, as they can be used in a nuclear weapon. The organizers of the second summit, however, have expanded the agenda to include issues pertaining to radioactive materials.