Becquerel discovered radioactivity by accident while studying a mineral containing uranium. He observed that with exposure to sunlight the mineral gave off a penetrating energy that exposed the film. While one day he tried the experiment one day the day was cloudy so he put it away in a dark dresser drawer and at the next day he found the picture of the mineral and later found out that the mineral did not need sunlight to expose radiation so he gave it to two young researchers that eventually isolated the two elements named polonium and radium.