Antoine Henri Becquerel was a French scientist born on December 15, 1852, and he died on August 25, 1908. He won the 1903 Nobel Prize in Physics along with Marie and Pierre Curie because he discovered radioactivity.
Education and career
Antoine Henri Becquerel was born on 15 December 1852 in Paris, France. His grandfather, Antoine César Becquerel, father, Edmond Becquerel, and later his son, Jean Becquerel, were all well-known physicists.
Becquerel studied at Lycée Louis-le-Grand before attending École polytechnique (1872–1874) and École des ponts et chaussées (1874–1877) to learn engineering. In 1888, he earned his Doctor of Science (D.Sc.) from the Sorbonne. His research focused on the polarization of light, including the process of phosphorescence and how light is absorbed by crystals.
In 1878, Becquerel worked as an assistant at the National Museum of Natural History. He became a Professor of Applied Physics there in 1892. In 1894, he was named chief engineer in the Department of Roads and Bridges. He also became a professor at École polytechnique in 1895.
Discovery of radioactivity
Becquerel’s discovery of spontaneous radioactivity is a well-known example of how chance can lead to important scientific findings when a person is prepared. Becquerel had been studying phosphorescence, which is the process where an object glows with light of one color after being exposed to light of another color. In early 1896, scientists were excited about Wilhelm Röntgen’s discovery of X-rays in late 1895. Röntgen found that the Crookes tubes he used to study cathode rays emitted a new kind of invisible ray that could pass through black paper. Becquerel learned about Röntgen’s discovery during a meeting of the French Academy of Sciences on January 20, where his colleague Henri Poincaré read Röntgen’s paper. Becquerel then began exploring whether phosphorescent materials, including uranium salts, might emit radiation similar to X-rays when exposed to bright sunlight.
In the first weeks of February, Becquerel placed coins or other objects on photographic plates, covered them with thick black paper, and placed phosphorescent materials on top. He then exposed these setups to sunlight for several hours. When he developed the plates, he saw clear shadows of the objects. On February 24, he shared his early results. However, on February 26 and 27, the weather was dark and overcast, so Becquerel stored his plates in a dark cabinet for those days. When he developed the plates on March 1, he made a surprising discovery: the shadows remained just as clear even without sunlight. William Crookes and Becquerel’s 18-year-old son, Jean, witnessed this finding.
By May 1896, after testing non-phosphorescent uranium salts, Becquerel concluded that uranium naturally emitted penetrating radiation without needing sunlight or other external energy. This led to intense research on radioactivity, including the discovery that thorium is also radioactive and the identification of polonium and radium by Marie and Pierre Curie. Becquerel published seven papers on radioactivity in 1896. His experiments also helped him study how radiation interacts with magnetic fields. He found that different radioactive substances deflected in different directions or not at all when placed in a magnetic field, showing that there are three types of radioactivity: negative, positive, and neutral.
Radioactivity was nearly discovered earlier, in 1857, when Abel Niépce de Saint-Victor, who was studying photography under Michel Eugène Chevreul, noticed that uranium salts could darken photographic emulsions. By 1861, Niépce de Saint-Victor realized that uranium salts emit invisible radiation. He knew Edmond Becquerel, Henri Becquerel’s father. In 1868, Edmond Becquerel wrote a book titled La lumière: ses causes et ses effets (Light: Its Causes and Its Effects). On page 50 of volume 2, he noted that Niépce de Saint-Victor observed that objects exposed to sunlight could leave shadows on photographic plates even in the dark. Niépce also noted that covering a surface exposed to sunlight with materials easily altered by light, like uranium nitrate, increased the effect.
On February 27, 1896, Becquerel described these findings to the French Academy of Sciences. However, further experiments led him to question and eventually abandon this earlier hypothesis. On March 2, 1896, he reported new findings.
Later life and death
In 1900, Becquerel studied the properties of beta particles and found that they had the same properties as fast-moving electrons coming from the nucleus. The next year, he discovered that radioactivity could be used in medicine. He placed a piece of radium in his vest pocket and noticed that his skin was burned. This discovery led to the creation of radiotherapy, which is now used to treat cancer.
Becquerel died on 25 August 1908 in Le Croisic at the age of 55. He died of a heart attack, but it was reported that "he had developed serious burns on his skin, possibly caused by handling radioactive materials."
Commemoration
The standard unit for measuring radioactivity is named after Becquerel. There is a crater on the Moon named after him, and there is also a crater on Mars named after him. A uranium-containing mineral called Becquerelite is named after him. A minor planet, numbered 6914 Becquerel, is named in his honor.