Radioactivity Discovered by Henri Becquerel in 1896
118 years ago in late February, French scientist Henri Becquerel was hard at work in his lab studying phosphorescent emissions stimulated by the Sun. After exposing uranium-bearing crystals to sunlight and placing them on a photographic plate, he correctly hypothesized that the crystal would produce its image on the plate. However, like any good scientist, he wanted to investigate his theory further. As the sun went down and the clouds set in, he placed his uranium sample and photographic plate in a drawer for another day.
Over the next few cloudy days, Becquerel was unable to do any work without a source of sunlight – so his materials continued to sit untouched in his drawer.
Finally on March 1, the sun came out and Becquerel was eager to get back to work. When he went to retrieve his materials, he was shocked to discover the uranium crystal had already left a clear, strong image on the plate – without any exposure to sunlight, or energy source to produce the image!
Although Becquerel attributed this reaction to “spontaneous emissions by the uranium” and did not pursue his findings any further at the time, what he had in fact discovered was radioactivity.
Years later, Marie and Pierre Curie became interested in Becquerel’s discovery, and decided to explore further. While experimenting with their own uranium-containing ore, they coined the term "radioactivity" to describe the resulting decay caused by the spontaneous emissions that they studied. Further investigation led them to discover how different types of decay produced different types of radiation, and that other chemical elements besides uranium contained radioactive isotopes. This led to the Curies’ isolation of two new elements, polonium and barium.
In 1903, Becquerel and the Curies together received the Nobel Prize in physics for their discovery of radioactivity and other contributions to this area.
The discoveries of these early scientists paved the way for new techniques to determine the age of the Earth, and more.