​​When Frédéric Joliot and Irène Joliot-Curie bombarded a thin | The Nobel Prize

​​When Frédéric Joliot and Irène Joliot-Curie bombarded a thin piece of aluminum with alpha particles (helium atom nuclei) in 1934, a new kind of radiation was discovered that left traces inside an apparatus known as a cloud chamber.

The pair discovered that the radiation from the aluminum continued even after the source of radiation was removed. This was because aluminum atoms had been converted into a radioactive isotope of phosphorus. That meant that, for the first time in history, a radioactive element had been created artificially.

The pair were awarded the 1935 Nobel Prize in Chemistry for their work "in recognition of their synthesis of new radioactive elements."