Grappling with the dirty bomb threat

President Obama has turned his focus to stockpiles of dangerous chemical and radiological materials that remain at risk of being stolen by terror groups planning to make a dirty bomb. However, the challenges are compounded by the potentially small size of such bombs and the widespread use of materials. "There are nuclear materials that are inadequately secured in dozens of countries all over the world," says Matthew Bunn of the Ploughshares-funded Belfer Center at Harvard and author of an annual report called Securing the Bomb.