Also even if it was never understood what was the first encounter with radioactive material?
Yes, actually. Miners working in Joachimsthal died of an unknown lung ailment at an alarming rate in the 1400s. These mines were likely filled with huge quantities of Rn. http://www-ns.iaea.org/tech-areas/communication-networks/orpnet/documents/cn223/8-chambers-keynote.pdf