Is it possible that the sodium nitrate is radioactivley causing the intense heat in the Atacama Desert?
That is entirely impossible. Sodium Nitrate, or NaNO3, is nothing that contains higher elements that can have nuclear decay and hence produce radioactivity. Naturally occurring radioactive materials (NORM) are coal (as it contains uranium and thorium as well as potassium-40, lead-210 and radium-226. However, the actual radioactivity levels are not great), mineral sands (which contain titanium and zircon, sometimes monazite, a rare earth mineral containing thorium), Tantalum concentrate (which usually contains uranium and/or thorium, but hardly ever reaches critical levels), oil and gas produce (radium-226, lead-210), and Radon gas which sometimes occurs naturally in caves. Now Radon is the best example that radioactivity does not directly have to do anything with heat! In Radon caves (which are sometimes used for healing purposes) the Radon gas cannot be smelled or felt, these caves are also rather cool. You are mixing up some things here: heat is produced in a radioactive chain reacti
