Leaders from around the world — some 47 countries — are in Washington this week for the Nuclear Security Summit, a gathering to talk about the threat of nuclear weapons ending up in the wrong hands. "If there was ever a detonation in New York City, or London, or Johannesburg, the ramifications economically, politically, and from a security perspective, would be devastating," said host President Barack Obama, pictured above, receiving acting Nigerian President Goodluck Jonathan. "And we know that organizations like al Qaeda are in the process of trying to secure a nuclear weapon — a weapon of mass destruction that they have no compunction at using," Obama warned. Since the passage of health care, nuclear has become a very hot topic. Last week, Obama signed an arms reduction treaty with Russia — setting off some political sparring on the president's policy. The day after that, consummately defiant Iran unveiled an advanced centrifuge system. Click HERE to read Huma Khan's full ABCNews.com report setting up the summit, including the intrigue around Israeli Prime Minister Benjamin Netanyahu's decision not to attend. Embedded below is the report we did last Wednesday "Loose Nukes," a Cynthia McFadden/Melia Patria look at the team of Americans whose job it is to find and secure loose nuclear weapon parts around the world. The story includes the removal process of enriched uranium in Chile, a job we were given exclusive access to film, at the time of the earthquake — making an already sensitive job that much more delicate. If you missed it, worth a watch given today's relevant news.