[5] In Becquerel's early career, he became the third in his family to occupy the physics chair at the Muséum National d'Histoire Naturelle in 1892.

[7] Becquerel's discovery of spontaneous radioactivity is a famous example of serendipity, of how chance favors the prepared mind.

He nevertheless proceeded to develop the plates on 1 March and then made his astonishing discovery: the object shadows were just as distinct when left in the dark as when exposed to sunlight.

"[11] As often happens in science, radioactivity came close to being discovered nearly four decades earlier in 1857, when Abel Niépce de Saint-Victor, who was investigating photography under Michel Eugène Chevreul, observed that uranium salts emitted radiation that could darken photographic emulsions.

[12][13] By 1861, Niepce de Saint-Victor realized that uranium salts produce "a radiation that is invisible to our eyes".

[15] Niepce further noted that on the one hand, the effect was diminished if an obstruction were placed between a photographic plate and the object that had been exposed to the sun, but " … d'un autre côté, l'augmentation d'effet quand la surface insolée est couverte de substances facilement altérables à la lumière, comme le nitrate d'urane … " ( ... on the other hand, the increase in the effect when the surface exposed to the sun is covered with substances that are easily altered by light, such as uranium nitrate ...

If one places between the phosphorescent substance and the paper a piece of money or a metal screen pierced with a cut-out design, one sees the image of these objects appear on the negative ... One must conclude from these experiments that the phosphorescent substance in question emits rays which pass through the opaque paper and reduce silver salts.

On 2 March 1896 he reported: I will insist particularly upon the following fact, which seems to me quite important and beyond the phenomena which one could expect to observe: The same crystalline crusts [of potassium uranyl sulfate], arranged the same way with respect to the photographic plates, in the same conditions and through the same screens, but sheltered from the excitation of incident rays and kept in darkness, still produce the same photographic images.

Henri made this discovery when he left a piece of radium in his vest pocket and noticed that he had been burnt by it.

[5] In 1908 Becquerel was elected president of Académie des Sciences, but he died on 25 August 1908, at the age of 55, in Le Croisic, France.

[6] He died of a heart attack,[9]: 49  but it was reported that "he had developed serious burns on his skin, likely from the handling of radioactive materials.

[5] In 1900, Becquerel won the Rumford Medal for his discovery of the radioactivity of uranium and he awarded the title of an Officer of the Legion of Honour.

[26] During his lifetime, Becquerel was honored with membership into the Accademia dei Lincei and the Royal Academy of Berlin.