Becquerel, Antoine-Henri (1852-1908)
Becquerel, Antoine-Henri (1852-1908)
Antoine-Henri Becquerel's landmark research on x rays and his discovery of radiation laid the foundation for many scientific advances of the early twentieth century. X rays were discovered in 1895 by the German physicist Wilhelm Conrad Röntgen, and in one of the most serendipitous events in science history, Becquerel discovered that the uranium he was studying gave off radiation similar to x rays. Becquerel's student, Marie Curie , later named this phenomenon radioactivity . His later research on radioactive materials found that at least some of the radiation produced by unstable materials consisted of electrons. For these discoveries Becquerel shared the 1903 Nobel Prize in physics with Marie and Pierre Curie . Becquerel's other notable research included the effects of magnetism on light and the properties of luminescence.
Becquerel was born in Paris on December 15, 1852. His grandfather, Antoine-César Becquerel, had fought at the Battle of Waterloo in 1815 and later earned a considerable reputation as a physicist. He made important contributions to the study of electrochemistry, meteorology , and agriculture. Antoine-Henri's father, Alexandre-Edmond Becquerel, was also scientist, and his research included studies on photography, heat, the conductivity of hot gases, and luminescence.
During his years at the Ecole des Ponts et Chaussées, Becquerel became particularly interested in English physicist Michael Faraday's research on the effects of magnetism on light. Faraday had discovered in 1845 that a plane-polarized beam of light (one that contains light waves that vibrate to a specific pattern) experiences a rotation of planes when it passes through a magnetic field ; this phenomenon was called the Faraday effect. Becquerel developed a formula to explain the relationship between this rotation and the refraction the beam of light undergoes when it passes through a substance. He published this result in his first scientific paper in 1875, though he later discovered that his initial results were incorrect in some respects.
Although the Faraday effect had been observed in solids and liquids, Becquerel attempted to replicate the Faraday effect in gases. He found that gases (except for oxygen ) also have the ability to rotate a beam of polarized light. Becquerel remained interested in problems of magneto-optics for years, and he returned to the field with renewed enthusiasm in 1897 after Dutch physicist Pieter Zeeman's discovery of the Zeeman effect—whereby spectral lines exposed to strong magnetic fields split—provided new impetus for research.
In 1874 Becquerel married Lucie-Zoé-Marie Jamin, daughter of J.-C. Jamin, a professor of physics at the University of Paris. She died four years later in March 1878, shortly after the birth of their only child, Jean. Jean later became a physicist himself, inheriting the chair of physics held by his father, grandfather, and great-grandfather before him. Two months prior to Lucie's death, Becquerel's grandfather died. At that point, his son and grandson each moved up one step, Alexandre-Edmond to professor of physics at the Musée d'Histoire Naturelle, and Antoine-Henri to his assistant. From that point on, Becquerel's professional life was associated with the Musée, the Polytechnique, and the Ponts et Chaussées.
In the period between receiving his engineering degree and discovering radioactivity, Becquerel pursued a variety of research interests. In following up his work on Faraday's magneto-optics, for example, he became interested in the effect of the earth's magnetic field on the atmosphere. His research determined how the earth's magnetic field affected carbon disulfide. He proposed to the International Congress on Electric Units that his results be used as the standard of electrical current strength. Becquerel also studied the magnetic properties of a number of materials and published detailed information on nickel, cobalt, and ozone in 1879.
In the early 1880s Becquerel began research on a topic his father had been working on for many years—luminescence, or the emission of light from unheated substances. In particular he made a detailed study of the spectra produced by luminescent materials and examined the way in which light is absorbed by various crystals . Becquerel was especially interested in the effect that polarization had on luminescence. For this work Becquerel was awarded his doctoral degree by the University of Paris in 1888, and he was once again seen as an active researcher after years of increasing administrative responsibility.
When his father died in 1891 Becquerel was appointed to succeed him as professor of physics at the museum and at the conservatory. The same year he was asked to replace the ailing Alfred Potier at the Ecole Polytechnique. Finally, in 1894, he was appointed chief engineer at the Ecole des Ponts et Chaussées. Becquerel married his second wife, Louise-Désirée Lorieux, the daughter of a mine inspector, in 1890; the couple had no children.
The period of quiescence in Becquerel's research career ended in 1895 with the announcement of Röntgen's discovery of x rays. The aspect of the discovery that caught Becquerel's attention was that x rays appeared to be associated with a luminescent spot on the side of the cathode-ray tube used in Röntgen's experiment. Given his own background and interest in luminescence, Becquerel wondered whether the production of x rays might always be associated with luminescence.
To test this hypothesis Becquerel wrapped photographic plates in thick layers of black paper and placed a known luminescent material, potassium uranyl sulfate, on top of them. When this assemblage was then placed in sunlight, Becquerel found that the photographic plates were exposed. He concluded that sunlight had caused the uranium salt to luminesce, thereby giving off x rays. The x rays then penetrated the black paper and exposed the photographic plate. He announced these results at a meeting of the Academy of Sciences on February 24, 1896.
Through an unusual set of circumstances the following week, Becquerel discovered radioactivity. As usual, he began work on February 26 by wrapping his photographic plates in black paper and taping a piece of potassium uranyl sulfate to the packet. However, because it wasn't sunny enough to conduct his experiment, Becquerel set his materials aside in a dark drawer. He repeated the procedure the next day as well, and again a lack of sunshine prompted him to store his materials in the same drawer. On March 1 Becquerel decided to develop the photographic plates he had prepared and set aside. It isn't clear why he did this—for, according to his hypothesis, little or no exposure would be expected. Lack of sunlight had meant that no luminescence could have occurred; hence, no x rays could have been emitted.
Surprisingly, Becquerel found that the plates had been exposed as completely as if they had been set in the sun . Some form of radiation—but clearly not x rays—had been emitted from the uranium salt and exposed the plates. A day later, according to Oliver Lodge in the Journal of the Chemical Society, Becquerel reported his findings to the academy, pointing out: "It thus appears that the phenomenon cannot be attributed to luminous radiation emitted by reason of phosphorescence, since, at the end of one-hundredth of a second, phosphorescence becomes so feeble as to become imperceptible."
With the discovery of this new radiation Becquerel's research gained a new focus. His advances prompted his graduate student, Marie Curie, to undertake an intensive study of radiation for her own doctoral thesis. Curie later suggested the name radioactivity for Becquerel's discovery, a phenomenon that had until that time been referred to as Becquerel's rays.
Becquerel's own research continued to produce useful results. In May 1896, for example, he found uranium metal to be many times more radioactive than the compounds of uranium he had been using, and he began to use it as a source of radioactivity. In 1900 he also found that at least part of the radiation emitted by uranium consists of electrons, particles that were discovered only three years earlier by Joseph John Thomson. For his part in the discovery of radioactivity Becquerel shared the 1903 Nobel Prize in physics with Curie and her husband Pierre.
Honors continued to come to Becquerel in the last decade of his life. On December 31, 1906, he was elected vice president of the French Academy of Sciences, and two years later he became president of the organization. On June 19, 1908, he was elected one of the two permanent secretaries of the academy, a post he held for less than two months before his death on August 25, 1908, at Le Croisic, in Brittany. Among his other honors and awards were the Rumford Medal of the Royal Society in 1900, the Helmholtz Medal of the Royal Academy of Sciences of Berlin in 1901, and the Barnard Medal of the U.S. National Academy of Sciences in 1905.
See also Geochemistry
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Antoine-Henri Becquerel was born the son of the physicist Alexandre-Edmond Becquerel, and the grandson of the physicist Antoine-César Becquerel, and it is not surprising that he followed in their footsteps. It is also not surprising that his research interests centered around solar radiation and phosphorescence, as these are phenomena that his father had investigated. He entered the École Polytechnique, in Paris, in 1872, which he left in 1874 and to which he subsequently returned. Becquerel received a doctorate degree from the Faculty of Sciences of Paris in 1888. In 1892, he was appointed professor of applied physics in the Department of Natural History at the Paris Museum, and in 1895, professor of physics at the École Polytechnique.
Becquerel's early work focused on plane-polarized light, the phenomenon of phosphorescence (in which certain compounds glow after being exposed to direct light), and the absorption of light by crystals. But all of his early research became overshadowed by his discovery of natural radioactivity. Although Becquerel did not initially comprehend what he was observing, his landmark discovery of radioactivity paved the way for a new understanding of the atom and atomic structure.
On February 24, 1896, Becquerel attended a meeting of the French Academy of Science and presented a short paper (one of the quickest methods in France at that time for disseminating results). One can well imagine Becquerel's excitement as he reported his results to the members of the academy.
One wraps a Lumiere photographic plate with a bromide emulsion in two sheets of very thick black paper, such that the plate does not become clouded upon being exposed to the Sun for a day. One places on the sheet of paper, on the outside, a slab of the phosphorescent substance, and one exposes the whole to the Sun for several hours. When one then develops the photographic plate, one recognizes that the silhouette of the phosphorescent substance appears in black on the negative. (Becquerel Comptes Rendus )
From this simple experiment, Becquerel concluded that the phosphorescent substance had to be emitting a type of ray that was passing through the paper and reducing the silver in the emulsion. This would seem to make sense, as the production of X rays, discovered a few years earlier by Wilhelm Röntgen, is accompanied by a soft glowing spot at the surface of the cathode ray tube. Becquerel decided to probe his unusual rays a little further. One week later, on March 2, 1896, Becquerel was back before the French Academy with the results of his further experiments. He had continued his experiments using a double sulfate salt of uranium and potassium
(potassium uranium sulfate monohydrate), which has a strong but short-lived phosphorescence.
He carefully wrapped his photographic plates in black paper, coating the paper with a crust of the uranium double salt, and upon exposure to sunlight he once again observed the "signature" of the phosphorescenceinduced rays. However, repeating the experiment on Wednesday, February 26, and Thursday, February 27, he was frustrated by two days of only intermittent sunlight. And because the Sun made no appearance on the two days following, on March 1 he developed his plates. Expecting to see only a faint silhouette resulting from the wrapped plates' intermittent exposure to sunlight, he was surprised to see that the silhouettes appeared with great intensity.
Becquerel suspected that the rays that produced the silhouettes emanated from the uranium salt itself, and that the small amount of sunlight was of no consequence. He arranged three more experiments, in which photographic plates were kept completely in the dark but put in direct contact with: (1) the salt; (2) a thin sheet of glass; and (3) a thin sheet of aluminum. He surmised that the glass would eliminate any possibility that a silhouette was the consequence of a chemical reaction, and that the aluminum would block the mysterious rays.
Developing the photographic plates, Becquerel observed an intensely defined silhouette on the first two plates, and a clear but considerably weaker silhouette on the third. Because he had double-boxed his plates inside his dark room and had placed the ensembles inside a drawer that he then closed, he was able to conclude that his mysterious rays were not related to phosphorescence and were not induced by sunlight.
It was another four years before Becquerel's radiation became understood as the production of β -rays (high energy electrons), but by then there was no question that Becquerel had discovered the instability of some atomic nuclei, and that he was richly deserving of the 1903 Nobel Prize that he shared with Pierre and Marie Curie.
see also Curie, Marie Sklodowska; RÖntgen, Wilhelm.
Todd W. Whitcombe
Asimov, Isaac (1989). Asimov's Chronology of Science and Discovery. New York: Harper & Row.
Farber, Eduard (1952). The Evolution of Chemistry: A History of Its Ideas, Methods, and Materials. New York: Ronald Press.
Leicester, Henry M. (1956). The Historical Background of Chemistry. New York: Wiley.
Becquerel, Antoine H. Comptes Rendus, translated. "On the Rays Emitted by Phosphorescence." Available from <http://webserver.lemoyne.edu/faculty/giunta>.
Becquerel, Antoine H. Comptes Rendus translated. "On the Invisible Rays Emitted by Phosphorescent Bodies." Available from <http://webserver.lemoyne.edu/faculty/giunta>.
Nobel e-Museum. "Antoine Henri Becquerel—Biography." Available from <http://www.nobel.se>.
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Antoine Henri Becquerel
Antoine Henri Becquerel
The French physicist Antoine Henri Becquerel (1852-1908) was the discoverer of natural radioactivity.
Antoine Henri Becquerel was born in Paris on Dec. 15, 1852. Both his father, Alexandre Edmond Becquerel, and his grandfather, Antoine César Becquerel, were scientists. Following his graduation from the École Polytechnique in 1874, Antoine Henri worked as a civil engineer, but he also retained a strong interest in scientific problems. In 1878 he succeeded in the chair of his father who was professor of applied physics at the Conservatoire des Arts et Métiers. Ten years later Becquerel earned his doctor's degree with a dissertation on the absorption of light in crystals. He then became professor of applied physics at the Museum of Natural History in Paris in 1892 and professor of physics at the Polytechnique in 1895.
Prior to 1895 Becquerel did research on phosphorescence. He had inherited from his father a supply of uranium salts, which were known to be phosphorescent when exposed to light. Upon learning in January 1896 about W. C. Roentgen's discovery of x-rays, Becquerel's interest immediately turned to the question of whether all phosphorescent materials acted as sources of similar rays.
The results did not justify his hopes, but Becquerel stumbled on an unexpected phenomenon. After placing sheets of sulfate of uranium on photographic plates wrapped in black paper, he exposed the package to light for several hours. On developing the plates he obtained distinct pictures of the uranium sheets. Later he obtained pictures of medals which had been placed between the uranium and the plates. The uneven thickness of the medals blocked in varying degrees the effectiveness of the radiation from uranium. He also discovered that part of the radiation could be deflected by a magnetic field and that the radiations had an ionizing effect on the surrounding air.
For the discovery of natural radioactivity, which for a number of years was called Becquerel rays, he won the Nobel Prize in physics in 1903. In his Nobel lecture Becquerel noted that the new radiation indicated the possible modification of atoms which "the methods at our disposal are unable to bring about (but which) could certainly release energy in sufficiently large quantities to produce the observed effects, without the changes in matter being large enough to be detectable by our methods of investigation." As a cause of that modification, he held out the possible existence of "an external radiation" hitherto undetected but which, when absorbed by radioactive materials, would be transformed into radioactivity without bringing about the transformation of the atoms themselves.
Becquerel's election as perpetual secretary of the Academy of Sciences in 1908 was one of the numerous honors bestowed on him. His death on Aug. 25, 1908, at Le Croisic did not signal the end of the lineage of scientists in the Becquerel family. From Becquerel's marriage to Lucie Zoé Marie Jamin a son, Jean, had been born; he became the fourth Becquerel to occupy the chair of physics at the Museum of Natural History and was also an able investigator of radioactivity.
The major work on Becquerel is in French. A detailed account of Becquerel's life is in Bessie Zaban Jones, ed., The Golden Age of Science: Thirty Portraits of the Giants of 19th-century Science by their Scientific Contemporaries (1966). Nobel Lectures: Physics, 1901-1921 (1964), published by the Nobel Foundation, includes a biographical sketch of Becquerel as well as his Nobel lecture on radioactivity. A biographical sketch is also contained in Niels Hugh de Vaudrey Heathcote, Nobel Prize Winners in Physics, 1901-1950 (1953). For background material see Harvey E. White, Classical and Modern Physics (1940). □
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Becquerel, Antoine Henri
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