[finnman69]

Hiroshim and Nagasaki were both relatively clean airbursts.

You blow up a dirty bomb laced with cesium or worse, cobalt, yes you could render all of Manhattan uninhabitable.

http://www.fas.org/faspir/2002/v55n2/dirtybomb.htm

[Reactionary]

Thanks for posting this information.

Given that the dust cloud from a cobalt bomb could disperse radition over three states in a pencil-shaped pattern, perhaps the Jihadists are planning on using them to symbolically "cut the US into three parts" using them.

They're quite fond of veiled references.