Civil engineers use something similar to verify the compaction around piping when we backfill after excavation work.
Up here someone stole one once, they put the fact that it was radioactive out in the media,(since I guess the thieves were too stupid to know what the symbol is for), and the next day someone left it outside of a post office.
We laughed and wondered if the cops thought of notifying the local hospitals about anyone who might be showing up in the emergency rooms wondering if they had radiation poisining, lol.