Dirty bombs aren’t really a thing one needs to worry about. Getting enough material to make one would require industrial nuclear material handling processes, otherwise you the bomb maker would die. Nuclear material heavy so it’s hard to get it up into the air, you’ll need a large bomb probably truck sized. So at this point you need to drive the thing around. Remember this thing is very radioactive, so you’ll need to shield the driver or they’ll be cooked before getting to their destination. You also need to avoid detection, and you won’t so you’ll need to work fast. Then once you blow up most of the material will fall out of the air really quickly, so you’ll want it somewhere populated like a city. Unfortunately all of the buildings keep the material from hitting many people, and anyone so unfortunate can just shower and take some iodine tablets. The explosion itself will cause most of the damage.
Once you’ve done this to little effect, the wrath of the whole world will fall on you for breaking this taboo. So it’s really not worth the trouble.
> Thus the consequences of this incident appeared to be less grave than in two earlier cases—in Brazil in 1987, and in Thailand in 2000—when unsuspecting scavengers who dismantled old radiotherapy machines exposed themselves and their families to very high doses of radiation. Four of the exposed people died in Brazil, and three in Thailand, and more were seriously injured. The cost of cleanup and recovery for their communities was substantial.
> Officials, especially in the United States, were relieved that the stolen Mexican capsule did not end up with terrorists, who could have used it to build a “dirty bomb.” Even though many planning scenarios predict that such a bomb would probably cause few radiation-related deaths, its economic impact could be disastrous.
Two previous incidents of material disappearing killed the thieves, and even still a dirty bomb isn't any more dangerous than a regular bomb to the intended victims. They're essentially not really a thing as I posted earlier. You'd probably just bake yourself trying to build one.
The actual danger to humans pales in comparison to stupid humans being irrationally afraid of a tiny statistical increase in the likelihood of cancer. Detonate a dirty bomb and you've created a zone that is difficult to remediate to the point where nobody would have any issues with living and working there.
Do it in a place like Manhattan and the cost to remediate would be potentially huge. We're not talking about turning an isolated former nuclear or chemical weapon production/storage facility into a nature preserve, but returning a 'slimed' dense urban area into one suitable for long-term human habitation. That's the real power of a radiological dispersal device.
Can't they just dig down? Are you saying some countries don't have bedrock?