Which scientist discovered the phenomenon of radioactivity?

French physicist Henri Becquerel studied the effect of luminescent materials activated by sunlight on photographic plates. During the experiments, the plates were wrapped in thick black paper. It was assumed that it would be possible to detect X-rays. It was found that blackening of the plates occurs even in cases where the luminescent material (potassium uranyl sulfate) was not irradiated, but simply stored nearby.
In May 1896, experiments were carried out with pure uranium. The impact was 3-4 times stronger than when working with uranium salts. The phenomenon has come to be known as Becquerel rays. Marie Curie later discovered that thorium had a similar effect. In the course of her joint work with Pierre Curie, radioactive elements – polonium and radium – were discovered.
In 1903, all three physicists were awarded the Nobel Prize. A. Becquerel was especially noted for the discovery of spontaneous radioactivity. The author of the term “radioactivity” is M. Curie.
Answer: A. Becquerel.