But the acquisition of radioactive material for a so-called 'dirty bomb,' which is radioactive material that is dispersed with a conventional explosive device, that is not that challenging.

VOA: standard.2009.05.01

Experts say terrorist groups are seeking materials for a crude nuclear device - a so-called "dirty bomb" - that would have limited blast potential but could spread radiation in a major urban area.

VOA: standard.2010.04.11