Henri Becquerel is one of the contributors to the discovery of radiation along with the Curies.
In 1898, the Curies discovered the existence of polonium and radium. They also contributed to the research in radiation, which is how Marie died to radiation poisoning.
Niels Bohr was the first person to develop a truly modern description of the atom. He worked with both electrons and radiation, and proposed that atoms emit radiation when electrons jump from allowed states in his model.
Image from https://en.wikipedia.org/wiki/Radiation