Irradiated Sand Bomb

I watched a documentary about the German plan to bomb the US during world war 2 using their Amerika Bomber, and it talked about that if they didn't have an atomic bomb in time, they'd use a weapon that consisted of irradiated sand wrapped around an explosive core, that would explode at medium altitude at rain down radioactive sand on the city below. Has anyone heard of this before, I can't find any information about it online, or even that sand could be irradiated.

yeah it was on history channel and some books on german military. The planes they wanted to drop the bomb with planes where way ahead of their time just planes on the drawing board planes that can go in to space.

[edit on 2-10-2004 by blacman2k6]