Take your self to a series of walmarts, buy ALL the smoke detectors you can, they all have sources. Package with explosive, voila - dirty bomb.
Big deal? not really, just needs cleanup. But, I just told you how to make one, Here, with materials from here.
There are times on this site where I just wait for an ignorant person to spew their crap...answer me 2 questions pal, #1, what state do you live in??? #2, describe in detail the last time you went through border patrol and / or customs???? radioactive material is not getting across our borders, no way, no how.....