@Terry
I get it, but it's stupid. Ukraine doesn't even need to use dirty bombs when russians were stupid enough to dirty themselves already, and will probably do it again if they try to mess with Chernobyl again.
@Hoss @Terry
Hard to say for sure. To some degree every country is aware of what kind of radioactive material everyone else has at their disposal, what kind of concentrations their bombs should have, what byproducts they'd produce etc. But if we're talking about a dirty bomb, I imagine you could easily mask it by just throwing in random stuff in there to throw off readings.