Unshielded but intact pebbles would emit extraordinarily high amounts of radiation that falls off with 1/r^2 by geometric attenuation. Picking them up and putti

Unshielded but intact pebbles would emit extraordinarily high amounts of radiation that falls off with 1/r^2 by geometric attenuation. Picking them up and putting them back in a shield would require remote handling (long tools and/or robots). But once they're all picked up and re-shielded, the radiation would be gone. Much different from spilling a vat of radioactive liquid which is much harder to clean.