Just to be clear, a nuclear warhead (including a suitcase nuke) generates blast effect either through nuclear fission or nuclear fusion. One additional effect is intense and relatively short half-life radiation. After a 2-4 week period in a suitably shielded shelter, one could emerge and live in that area.

A dirty bomb is a conventional explosive that is packed in a radioactive material. When detonated, the radioactive material is disseminated in the area surrounding the explosion. The residual radiation may persist for decades.

Two different events entirely.