Here is a brief video demonstration of nuclear contamination and how it’s measured.
This video also nicely demonstrates that once the source of radioactivity is removed from an area, the area is no longer considered “radioactive.”
The counter used here is the Ludlum Model 3, and the probe is the Eberline Tungsten HP-210. This setup is used by professionals, but these are from my personal collection (Ebay has been good to me). NoSalt contains Potassium (as a Sodium salt substitute) and therefore is just radioactive enough for a demonstration like this. The radiation emitted by potassium is minimal and not a cause for concern.
Mikl Moose 