Antoine Henri Becquerel
1852-1908
French Physicist
Henri Becquerel had already established himself as a respected French physicist when his discovery of radioactivity, in 1896, catapulted him into the ranks of the world's leading scientists. Although the discovery was unexpected, it was not random. Becquerel's background, experience, and particular circumstances positioned him for this historic event.
His background began with his ancestors. Becquerel's father, Alexandre Edmond Becquerel (1820-1891), and his grandfather, Antoine César Becquerel (1788-1878), had each been the physics professor at the Natural History Museum in Paris. Edmond Becquerel was especially interested in phosphorescence. He assembled a large collection of luminescent minerals for the Museum.
Edmond Becquerel's son, Antoine Henri (known as Henri), decided to follow the path that his father and grandfather had chosen. This path gave him the experience, and later the professional positions, that proved to be crucial forhis future. Henri Becquerel entered the Paris Polytechnical School in 1872, where he earned an engineering degree. In 1878 he became his father's assistant at the Natural History Museum.
Henri Becquerel investigated the magnetic properties of different substances and the effects of magnetism on light. He also studied infrared spectra, luminescence, and absorption of light. For his researches he was awarded the doctorate in 1888. Becquerel was elected to the French Academy of Sciences in 1889. He was also named to the French Legion of Honor.
Becquerel became professor at the Museum in 1892, after his father's death. He was also appointed to his father's position at the National Conservatory of Arts and Trades. In 1895 Becquerel received his third professorship, this time at the Polytechnic School, where his father and grandfather had previously held the post. He continued to work at all three institutions simultaneously. He was named chief engineer of bridges and highways in 1894.
Early in 1896 Becquerel heard a talk that would forever change his life. A German physicist had just discovered invisible rays that could pass through opaque objects. Becquerel learned that the invisible rays seemed to come from the phosphorescent screen used in the experiments. It was natural to wonder whether other phosphorescent materials might also produce these rays (later called x rays).
Becquerel returned to the Museum and began testing the specimens in his father's collection of phosphorescent minerals. He soon found that uranium minerals emitted invisible rays, which he believed were a form of light. He published his findings during 1896-1897.
At first most scientists were not very interested in Becquerel's rays, since their journals were being flooded with reports of all sorts of invisible rays. Becquerel himself turned to the newly discovered Zeeman effect in 1897, since it related to his researches of magnetism's effects on light. He was drawn back to his rays after Marie Curie (1867-1934) and Pierre Curie (1859-1906) used them to trace and identify two new elements, polonium and radium (1898). Around that time Becquerel was recognized as having discovered a new property of matter, which Marie Curie named radioactivity.
Along with several other researchers, Becquerel found that part of the rays emitted by radium were beams of electrons (1900). In 1901, checking to see whether uranium's rays might come from an impurity, Becquerel separated a radioactive substance from uranium, leaving the uranium inactive. Amazingly, the uranium eventually regained its original activity. This information helped Ernest Rutherford (1871-1937) and Frederick Soddy (1877-1956) to develop a revolutionary theory of radioactive transmutation in 1903.
Radioactivity became a popular subject for research. Later it would develop into the field of nuclear physics. Becquerel's earlier finding that rays from uranium could affect electrified bodies (the process was later called ionization) was essential for radioactivity studies. However, Becquerel no longer was in the forefront of the field, and he eventually returned to his earlier interests of phosphorescence and light spectra.
For his discovery of radioactivity Becquerel shared the 1903 Nobel Prize in physics with Marie and Pierre Curie. He was also honored by election as vice president, president, and permanent secretary of the Academy of Sciences.
Becquerel's first wife, Lucie-Zoé Jamin, was the daughter of a noted French physicist. She died soon after the birth of their son Jean in 1878, and Becquerel later remarried. After Henri Becquerel's death, Jean Becquerel was named to the physics chair at the Natural History Museum, the fourth generation of his family to hold that position.
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