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? Unless of course it's such a strong emitter that it's glowing in the dark and already looking distinctly unhealthy to all and sundry?
The point being that someone smuggling radioactives is hardly likely to stick them conveniently on the outside of the box.
Or did I misunderstand something fundamental in either the piece, or in 40-year-old A-level physics?