Re: Not a nuclear scientist here...
"but isn't the significant thing about an alpha decaying radioactive source the fact that alpha particles don't go all that far in air, and can be stopped in general by even packaging, let alone shielding?"
On the one hand, yes. But on the other hand, that applies to any method you might try to use to detect stuff. So this method won't be any worse in that respect, but may have benefits over other detection methods in other ways.
Exactly why they think anyone is smuggling large quantities of radioactive materials through American ports is a more difficult question to answer.
Biting the hand that feeds IT
