The device's primary source of neutron radiation was the radioactive element californium, but the stream of neutrons produced by the californium was multiplied by passing it through a lattice of highly enriched uranium U-235, whose nuclear fission released additional neutrons.

CNN: SHARE THIS

The GAO is giving good marks to those 10-mile response systems, saying that the primary health risk in those zones is exposure to radiation.

FORBES: Nuclear Energy Radiating on Capitol Hill