Explanation

Radioactivity was discovered by Henri Becquerel in 1896

They discovered radioactivity proving that the uranium emitted radiation without an external source of energy such as the Sun

Marie Curie with her husband Pierre Curie, coined the term radioactivity 

in 1903, Henry Becquerel shared the Nobel Prize for Physics with Pierre and Marie Curie

Ernest Rutherford did many experiments studying the properties of radioactive decay (alpha, beta, and gamma)