Narrator: This is Science Today. In an ongoing effort to strengthen our nation's defense against terrorism, scientists at the Lawrence Livermore National Laboratory are testing commercial instruments and developing new technologies to detect if nuclear materials have been smuggled inside cargo containers. Arden Dougan, a program manager at the Lab, says handheld radiation detectors are being used for what's called active interrogation.

Dougan: The active interrogation method uses neutrons to go inside the container and that makes the nuclear material fission and when it fissions, new signatures of radiation exit the cargo container, we detect that and from that we can say 'A-ha, there's something inside." And so we're looking at various techniques to look inside that container.

Narrator: This includes what Dougan calls defense and depth strategies.

Dougan: It's kind of a layered approach for security, where you don't just use one super detector that detects everything inside a container, you have different kinds of detectors that are each specialized or maybe overlap what they detect.

Narrator: For Science Today, I'm Larissa Branin.