Röntgen discovered x-rays, and Becquerel discovered radioactivity. (jan 1, 1895 – 23h 59min, dec 31, 1895 y)

Description:

They utilized cathode rays and uranium-enriched substances.
Röntgen found that radiation penetrated matter, darkened photographic plates and caused fluorescence. He also discovered that x-rays couldn't be deflected by a magnet and therefore couldn't contain charged particles.
Becquerel accidentally discovered that exposing wrapped photographic plates to a uranium compound caused them to darken even without cathode rays. This spontaneous emission of particles and/or radiation was named radioactivity

Added to timeline:

Date: