Yes, but Charlie got the math wrong. It's a lot less than he suggests.

See: https://news.ycombinator.com/item?id=12329322

In addition, if we are talking "gram sized" projectiles, they likely have a front cross sectional area on the order of 10^-4 m^2 or less. That means that we are talking about 16 milliCuries or so. That's about the amount of radiation in a single medical imaging dose, or as much alpha emission as 1000 smoke detectors.