3.An "enhanced radiation" warhead is just what it says, a nuclear weapon where the design has been "tweaked" so that a larger fraction of the energy release from fission/fusion comes out of the bomb case as radiation.
5.A: There are a few events which cause extreme levels that will never go away, but most radiation from things like blown up cars (nuclear engines) and the mini-nuke weapon will dissipate given a little time.
