That isn't true. It is actually less radioactive than plutonium. And plutonium can be worked with without special shielding:
During the Manhattan project the core of the "Gadget" (plutonium) was transported to the Trinity Site in the back seat of a car by a physicist who held it in his lap.
I think the author is instead postulating that it is extremely dangerous because it's much easier to make an a-bomb with it than plutonium.