Becquerel, HA
ACHIEVEMENT(S): Discovered radioactivity
NICKNAME/ALIAS: None
DATE/PLACE OF BIRTH: 15 December 1852, at Paris, France
DATE/PLACE/AGE AT DEATH: 25 August 1908, in Le Croisic,
France. Aged 55
DISCIPLINE: Physicist
FIELD: Physics
LANGUAGE: French
PARENTS: Alexandre-Edmond Becquerel (1820-91) and ?
SIBLINGS: ?
SPOUSE: Lucie-Zoe-Marie Jamin (d. 1878), married 1874; Louise Desiree
Lorieux, married 1890
CHILDREN: Jean (1878-1953)
EDUCATION: Lycee Louis-le-Grand, 1864-72; Ecole Polytechnique, Paris,
1872-74; Ecole des Ponts et Chaussees, 1874-77
MAJOR WORK: "Emission de radiations nouvelles par l'uranium metallique", 1896
LIFE AND TIMES:
From 1882-88, Becquerel extended his father's studies on luminescence (the emission of light from unheated substances), by studying the relation between absorption of light and emission of luminescence in some uranium compounds. In particular, he developed a new method for analysing spectra (the displays of the various wavelengths emitted by light sources), and then made a detailed study of the spectra produced by luminescent materials, and the way in which light is absorbed by various crystals.
In 1888 he received his doctorate from the University of Paris for a dissertation on the absorption of light in crystals, and the following year he was elected a member of the Academie des Sciences.
In late 1895, the German physicist Roentgen* discovered the highly energetic and penetrating radiation, known today as X-rays, which is generated when cathode rays (electrons) emitted by the negative electrode (cathode) of a vacuum tube strike another portion of the tube during a high-voltage electric discharge. The mathematician JH Poincare* told Becquerel of this discovery, and in particular that X-rays were emitted from a luminescent spot on the side of Roentgen's glass cathode ray tube. This fact immediately suggested to Becquerel that X-rays might be produced naturally by luminescent crystals.
In order to test this hypothesis, in 1896 Becquerel decided to investigate whether luminescent materials activated by light rather than by cathode rays would also emit X-rays. He placed photographic plates wrapped in thick black paper up against a known luminescent material, potassium uranyl sulfate (a uranium salt), and exposed the package to sunlight for several hours.
On developing the plate, Becquerel found it to be fogged (with a silhouette of the mineral samples clearly visible) and concluded that the ultraviolet rays in sunlight had caused the uranium salt to luminesce and give off X-rays, that had penetrated the paper and exposed the plate.
After announcing his results at a meeting of the Academie des Sciences on 24 February 1896, Becquerel then tried to repeat the experiment, but the weather remained continually cloudy, so he set aside the package in a dark drawer until 1 March when he decided to develop the photographic plates anyway.
To his amazement, he found that the plates had been exposed as completely as if they had been placed in sunlight, and he immediately realized that some form of radiation - but not X-rays - had been emitted from the uranium salt and exposed the plates.
Over the next few months he found that these "Becquerel rays", as they were known for a time, behaved like X-rays in penetrating matter and ionizing air. He repeated his experiment with other luminescent materials and found that only uranium compounds emitted the spontaneous radiation he had discovered, and that non-luminescent uranium compounds produced the same emissions, proving that radiation was not linked to luminescence.
In May 1896, Becquerel then found that uranium* metal was three to four times more radioactive than the compounds of uranium, and during this year published seven papers on his discoveries.
Becquerel's advances in his research prompted one of his graduate students, Marie Curie*, to study radiation for her doctoral thesis, and she later suggested the name ‘radioactivity’ for Becquerel's discovery.
From her investigations in collaboration with her husband, Pierre Curie, in 1898 Marie Curie discovered (simultaneously with Gerhard Carl Schmidt) that thorium was also radioactive, and then managed to isolate two new highly radioactive elements, which they named polonium and radium.
In 1900, Becquerel then subjected the radiation from radium to electric and magnetic fields and was able to prove by measuring the deflection of the radiation beta particles that these beta particles were in fact the same as the electrons discovered by J.J. Thomson* in 1897, and that radioactivity consists in part of a stream of electrons. Becquerel also discovered that radioactivity could be removed from a radioactive material by chemical action, but that the material then regained its radioactivity.
He also found evidence that radioactivity causes the transformation of one element into another. Finally, in 1901, his report on the physiological effects of radiation (after an active sample of the Curies' radium carried in a pocket caused burns) inspired investigation that led ultimately to medical use.
ASSESSMENT: His discovery of radioactivity was instrumental in the development of nuclear physics.
EXTRA CONNECTIONS: His work related to that of C.T.R. Wilson*, Ramsay*
ONELINER: Henri Becquerel, discoverer of radioactivity
BIBLIOGRAPHY:
DSB, EB
Tyler Wasson (ed.), Nobel Prize Winners, 1987
Newton, David E., Notable Twentieth Century Scientists, ed. Emily J. McMurray, New York & London: Gale Research, 1995