Reply #11: Actually, it IS that easy

[Xithras]

The designs for a Little Boy type bomb are all over the Internet (Google it and you can find a diagram in under two minutes), but this style of weapon isn't likely to be used by any terrorist with a brain.

The Little Boy design was abandoned because it was grossly inefficient...something less than 20% of its fissionable material actually detonated (it may have been less, but I studied this a long time ago). It's hard to believe that a terrorist group would go through the trouble of creating that much fissionable uranium just to turn around and waste 80% of it on such a primitive weapon. Implosion-type nuclear bombs deliver an equally big bang at a fraction of the fissile material cost.