I did a bit more reading, and found this crazy and scary graph. It's under "Uranium-232 Series Activity" near the bottom of this paper[1]. It shows that gamma ray output from U-238 increases > 5x a year after U-238 is first refined, and stays higher than originally was for >100 years.
It's due to the decay products of U-238 (and their decay products) all producing radiation that adds up to more than the original's.
I never would have guessed that.