Henri Becquerel Essay, Research Paper

Henri Becquerel

Henri Becquerel, a French physicist, was born in Paris on December 15, 1852. His grandfather, Antoine-Cesar 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. Henri father, Alexander-Edmond Becquerel, also made a name for himself in science. His research-included studies on photography, heat, and the conductivity of hot gases, and luminescence.

Becquerel?s early education took place at the Lycee Louis-le-Grand from which he graduated in 1872. He then enrolled at the Ecole Polytechnique, and two years later he moved on to the Ecole des Ponts et Chaussees (Bridges and Highways School). In 1875 he started teaching at the Polytechnique and later he succeeded his father Alexander ?Edmond Becquerel in the Chair of Physics at the Natural History Museum. He was an expert in fluorescence and phosphorescence, continuing the work of his father and his grandfather.1

The period of quiescence in Becquerel?s research career came to an end in 1895 with the announcement of Rontgen?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. Becquerel wondered whether the production of X rays might always associated with luminescence.2

To test this hypothesis, Becquerel exposed fluorescent uranium salt, pitchblende, to light and then placed it on a wrapped photographic plate. He found that a faint image was left on the plate, which Becquerel believed was due to the pitchblende emitting the light it had absorbed as a more penetrating radiation. Accidentally Becquerel left a sample that had not been exposed to light on the top of a photographic plate in a drawer. He noticed that the photographic plate also had a faint image of the pitchblende. After several chemical tests he concluded that these ?Becquerel rays? were a property of atoms. He had accidentally discovered radioactivity and prompted the beginning of the nuclear age.3

With this discovery of this new radiation Becquerel?s research gained a new focus. His advances prompted his graduate student Marie Curie to understand 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 of 1896 Becquerel found uranium metal to be many times more radioactive than the compounds of uranium he had been using and began to use it as a source of radioactivity. Becquerel demonstrated that the radiation emitted in uranium shared certain characteristics with X-rays but unlike X-rays could be deflected by a magnetic field and therefore must consist of charged particles.4

On February 24, 1986, he reported to the Academy that fluorescent crystals of potassium uranyl sulfate had exposed a photographic plated wrapped in black paper while they both lay for several hours in direct sunlight. On March 2, Bacquerel reported comparable exposures when both crystals and plate lay in total darkness.

Becquerel did not neglect his general studies. He showed that, like X rays, crystals could ionize the air they passed through. He found evidence to suggest that the rays were refracted and reflected like visible light, although later he attributed these effects to secondary electrons ejected from his glass plate and mirrors. However, he devoted a substantial amount of effort to searching out the radiation that had first excited his penetrating rays. He kept some of his crystals in the darkness, hoping that their pent-up energy might spread itself and reexcite themselves. He tried other luminescent crystal and found that only those containing uranium emitted the penetrating radiation.5

With this last announcement, on May 18, Becquerel?s discovery of radioactivity was complete, although he continued with ionization studies of his penetrating radiation until the following spring. Becquerel established the occurrence and the properties of that radiation, so that it could be identified clearly. He also showed that the power of emitting penetrating rays was a particular property of uranium. However, the implication of this second conclusion was by no means clear at the time. Becquerel characterized his own achievement as the first observation of phosphorescence in a metal.6

Marie Curie?s work, which attracted Becquerel?s attention, brought her and her husband within the circle of his acquaintance and turned him back to radioactive studies. He became the mediator through whom their papers reached the Academy, and they lent him radium preparations from time to time. Toward the end of 1899 Becquerel began to investigate the effects of magnetic deflection of the beta rays from short-term decay products in equilibrium with the radium.7

In July of 1900, Becquerel was successful in reducing that radiation, in one specimen, to one-sixth of its original value. In confirmation of this result, he found that earlier that spring, Crookes had succeeded by more effective chemical procedures, in separating from uranium the photographically active radiation, which he now attributed to a substance provisionally named uranium X. One year later Becquerel realized the logical incongruity of these two successes. It had been relatively easy to remove the apparent radioactivity from uranium by chemical purification, yet no one who had investigated uranium over the last five years had ever observed a nonradioactive specimen. It followed, then, that whatever radioactivity was lost in purification must always regenerate itself; and he verified this logical conclusion on his own earlier specimens. The uranium had regained its lost radioactivity, and barium sulfate precipitates had lost all that they had carried down. The explanations he attempted were thoroughly confusing, but the facts remained.8

In December 31, 1906, Becquerel was elected vice-president of the Academy of Sciences, serving in that capacity during 1907 and succeeding to the presidency in 1908. In June 1908 he was elected as one of two permanent secretaries of the Academy. In 1903 Becquerel shared the Nobel Prize in physics with the French physicist Pierre Curie and Marie Curie for their work on radioactivity.

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 the U.S. National Academy of Sciences in 1905. Some of Becquerel works include Recherches sur la phosphorescence (Research on Phosphorescence, 1882-1897) and Decouverte des radiations invisibles emises par l?uranium (Discovery of the Invisible Radiation Emitted by Uranium, 1896-1897). 9

He was married to Mlle Janin, the daughter of a civil engineer. They had a son

Jean, 1878, who was also a physicist: the fourth generation of scientists in the

Becquerel family..

Antoine Henri Becquerel died at Le Croisic on August 25, 1908.

Endnotes

1. Dictionary of Scientist (pg42)

2. Notable Twentieth-Century Scientist (pg134)

3. Dictionary of Scientist(pg42)

4. Notable Twentieth-Century Scientist(pg134)

5. Dictionary of Scientific Biography(pg559)

6. Dictionary of Scientific Biography(pg559)

7. Notable Twentieth-Century Scientist(pg135)

8. Notable Twentieth-Century Scientist(pg135)

9. Microsoft Encarta 98 Encyclopedia

Microsoft Encarta 98 Encyclopedia: Microsoft Corporation.

1993-1997

Muir, Hazel. Dictionary of Scientists: Larousse Inc.

New York 1994

Dictionary of Scientific Biography: Volume I, Charles Scribner?s Sons.

New York 1970

Notable Twentieth-Century Scientist: Volume I A-E, Gale Research Inc.

Chicago 1995