Henri Becquerel
Henri Becquerel was the first person who made the first breakthrough in discovering radioactivity. One of the elements he used happened to be uranium. He put a slate and penny in black paper. Then he folded the paper over it, poured uranium over it, covered it with more black paper, and later he poured water over it and lifted it and a faint outline of the slate and penny were in the center. When Becquerel died, a scientist named Marie Curie took over.