Henri Becquerel (1852 - 1908)

Current Atomic Model

1. Discovered nuclear radiation in 1896.
2. Becquerel was studying phosphorescence (the phenomenon which allows certain toys to glow in the dark after absorbing some light). He thought phosphorescence was related to x-rays, a newly discovered form of radiation. Some uranium compounds were phosphorescent, so he happened to be experimenting with them.
3. To test his idea that phosphorescence was related to x-rays, he sealed a photographic plate in black paper to prevent it from being exposed to visible light. It was known that x-rays could penetrate paper, so Becquerel would put a uranium compound in the form of a mineral rock on top of the paper and place these both out in the sun. The idea was that the sun would cause the rock to become phosphorescent, thus giving off x-rays and exposing the plate through the paper.
4. His idea worked (or so he thought). The uranium containing rock made an outline of itself on the photographic plate through the sealed paper. However, a series of cloudy days had passed and his next experiment was sitting in a desk drawer preventing the uranium from being exposed to light which prevented it from giving off light due to phosphorescence.
5. Without exposing the plate and uranium to light, he developed the photographic plate and found to his astonishment that the uranium still exposed the plate through the paper even though the uranium hadn't given off any phosphorescent light. This meant that phosphorescence was not the reason the plate was being exposed and that the uranium was giving off some kind of radiation which could penetrate through the paper wrapped around the photographic plate.

Marie Curie (1867-1934)

Current Atomic Model

1. Shortly after this discovery Marie Curie began experiments with uranium to determine the nature of this "radioactivity", a term coined by her. Her husband also turned his research toward the understanding of radiation. In 1903, Marie and Pierre Curie and Henri Becquerel received the Nobel prize for their work in radioactivity.
2. These experiments laid the groundwork for a new era of physics and chemistry. Eventually this would lead to the discovery of the neutron.