'Dirty Bomb' Sting Finds a Hole in Security  Undercover
investigators obtained a license to buy enough radioactive
material to build a "dirty bomb," amid little scrutiny from
federal regulators, according to a government report obtained
Wednesday. The U.S. Nuclear Regulatory Commission issued the
license to a fake company in just 28 days, with only a cursory
review, the Government Accountability Office says.      And I'm
Melissa Block.  Today, congressional investigators reported the
results of an unusual sting operation. Working undercover, they
set up a fake company and obtained a license for purchasing
radioactive materials, the kind that could be used by terrorists
in the dirty bomb.  NPR's David Kestenbaum reports.  DAVID
KESTENBAUM: You can buy smoke detectors from the supermarket
that have small radioactive sources inside them. But to buy more
powerful sources, you need a license from U.S. Nuclear
Regulatory Commission. Some members of Congress wanted to see
how hard that would be, so they asked invest