Henri Becquerel (December 15, 1852-August 25, 1908) was a French physicist. He was awarded the 1903 Nobel Prize in Physics for the discovery of natural emissive phenomena.

At that time, Becquerel's material of choice was uranium and potassium bissulfates. He exposed the two materials to sunlight, and then wrapped the exposed materials and photosensitive negative with black paper. After a period of time, the negative was developed to show images of uranium crystals.

Becquerel concluded: "The radiation emitted by phosphorescent materials can pass through opaque paper." At first, he thought that uranium would absorb energy from the sun and then emit X-rays.

On February 26 and 27, 1896, it was cloudy over Paris. Becquerel originally planned to dry the wrapped uranium and photographic plates in the sun, so he had to return them to the drawer. When he developed the negatives on March 1, he thought that he could only see vague images, but unexpectedly he saw very clear images, which surprised him. Uranium can emit radiation without requiring external energy sources such as sunlight, so he discovered radioactivity and emitted radiation spontaneously from materials.

Comments: The problem he accidentally discovered made him a famous scientist.