Question

What is radioactivity and how did Henri Becquerel discover it?

Answer 1

Radioactivity is the emission of ionizing radiation or particles caused by the spontaneous disintegration of atomic nuclei.
Antoine Henri Becquerel discovered it by conducting an experiment which started with the exposure of a uranium-bearing crystal to sunlight. Once the crystal had sat in the sunshine for a while, he placed it on a photographic plate. For a couple of days he left his sample of uranium in a closed drawer along with the photographic plate. When the weather had cleared, he returned to the drawer to retrieve his gear. He found that the crystal had left a clear, strong image on the photographic plate. He discovered that a piece of mineral which contained uranium could produce it's image on a photographic plate in the absence of light. and thus he discovered was radioactivity...He attributed this phenomenon to spontaneous emission by the uranium.