Becquerel Wins the Nobel Prize for Discovering Natural Radioactivity
Antoine-Henri Becquerel is renowned for his pivotal discovery of natural radioactivity, a breakthrough that significantly advanced the field of nuclear physics. This discovery emerged in the context of late 19th-century scientific exploration of electromagnetic radiation, which included the earlier discoveries of visible light, infrared, and X rays. Influenced by Wilhelm Röntgen’s discovery of X rays, Becquerel conducted experiments with uranium crystals, initially hypothesizing that ultraviolet light would trigger X rays. Surprisingly, he found that uranium emitted penetrating rays even in complete darkness, leading to his announcement of radioactivity on May 18, 1896.
Becquerel's work laid the groundwork for further research into radioactive elements and their properties, inspiring subsequent investigations by notable scientists like Marie and Pierre Curie, and Ernest Rutherford. In recognition of his groundbreaking contributions, Becquerel was awarded the Nobel Prize in Physics in 1903, alongside the Curies. His discovery not only captivated the scientific community but also opened new avenues for understanding atomic structure and the fundamental nature of matter, marking a significant turning point in scientific history.
Becquerel Wins the Nobel Prize for Discovering Natural Radioactivity
Date December 10, 1903
Antoine-Henri Becquerel was awarded the Nobel Prize in Physics for his discovery of the phenomenon of natural radioactivity.
Locale Stockholm, Sweden
Key Figures
Antoine-Henri Becquerel (1852-1908), French physicistMarie Curie (1867-1934), Polish-French physicist and chemistJoseph John Thomson (1856-1940), English physicistHeinrich Hertz (1857-1894), German physicistErnest Rutherford (1871-1937), British physicistFrederick Soddy (1877-1956), English chemist
Summary of Event
The discovery of radioactivity is only part of the larger story of scientific investigations of the electromagnetic spectrum and is intimately connected with the discovery of X rays. During the final two decades of the nineteenth century, building on the theoretical foundations of James Clerk Maxwell, scientists explored the nature of a variety of electromagnetic radiation. If Maxwell’s theories were correct, it would be possible to produce electromagnetic radiation through a moving electrical charge. In 1887, Heinrich Hertz attempted such an experiment and was the first to identify radio waves. This largely completed the electromagnetic spectrum to include visible light, infrared radiation (discovered earlier by William Herschel), and ultraviolet radiation (discovered by Johann Wilhelm Ritter). By 1890, the spectrum of electromagnetic radiation extended from the long-wavelength radio waves to the extremely short-wavelength ultraviolet rays. The missing member of this family was X rays, which completed the electromagnetic spectrum. In 1895, Wilhelm Conrad Röntgen, while experimenting with a cathode-ray apparatus, discovered a powerful ray that penetrated thick paper as well as thin metals. Called “X ray” because of its unknown composition, this radiation had the ability to penetrate materials, and its power and mystery captured the imagination of both the public and other scientists. Antoine-Henri Becquerel was one of the scientists whose imaginations were triggered by this event.
For several generations, the Becquerel family had been involved closely with science in France. Becquerel’s father and grandfather were both distinguished scientists, and he followed in their footsteps. Becquerel’s early research focused on optics; later, he shifted to infrared radiation and finally to the absorption of light in crystals. He completed his doctoral dissertation in 1888, and in 1889 he was elected to the Academy of Sciences. During the following years, Becquerel undertook few research projects but moved actively through the academic ranks. He held an unprecedented three chairs of physics at different institutions at the same time and became chief engineer for the Department of Bridges and Highways.
By 1896, Becquerel was one of the most successful and powerful scientists in France, and yet none of his accomplishments could be considered a major contribution to the history of science. His interest in research was revived by Röntgen’s discovery of X rays. Becquerel concluded that, given that X rays were generated through the use of the cathode-ray tube along with visible light and that both X rays and light were found at the place where the beam produced a fluorescent pattern, X rays and light may be produced by the same mechanism. (It turned out that fluorescence was purely incidental to the production of X rays.) He began to search for materials other than glass that could be made to fluoresce through the use of ultraviolet light. His earlier work with crystals brought to mind a uranium-potassium-sulfate compound that possessed such qualities. He exposed to sunlight a photographic plate wrapped in light-proof papers with the uranium crystals placed on top. He had hoped that the ultraviolet rays of sunlight would trigger the crystals to produce X rays and expose the photographic plate. On developing the plate, Becquerel found it blackened by some penetrating rays.
One week later, Becquerel decided to set a control for his experiment by repeating the procedure in total darkness. Much to his surprise, the photographic plates were exposed again. This result violated his working hypothesis: that ultraviolet rays triggered the production of X rays in the uranium crystal. In the weeks that followed, Becquerel considered a number of alternative explanations for this contradictory result. He thought there was a possibility of residual effects from the initial experiment, so he isolated his crystals in the dark for some time. The effect, however, remained the same. Becquerel tested other luminescent crystals, but he could not reproduce the results. This led him to test nonluminescent uranium compounds, which produced penetrating rays, and finally he tried a disk of pure uranium and found the penetrating radiation several times as intense. On May 18, 1896, Becquerel announced the discovery of radioactivity.
In 1897, Becquerel completed a series of studies to separate other possible sources for this radiation and to establish the properties of this form of radiation. He was able to show that the presence of the penetrating rays was a particular property of uranium. He also found that the emission of the rays from the uranium was continuous and independent of any external source. The discovery of radioactivity produced a response equal to that of the discovery of X rays. Laboratories immediately began extensive examination of this new phenomenon. After his discovery of radioactivity, Becquerel continued his pioneering work in nuclear physics with the identification of electrons in the radiation of radium and produced the first evidence of the radioactive transformation. In 1903, Becquerel and his student Marie Curie were awarded the Nobel Prize in Physics.
Significance
The discovery of radioactivity opened up a new world of nuclear physics. At the Cavendish Laboratory in England, Sir Joseph John Thomson and his colleague Ernest Rutherford began to study the ionizing powers of the newly identified rays. Rutherford discovered that uranium exhibited two kinds of radioactive rays: alpha rays, which had low penetrating powers, and beta rays, which possessed greater abilities to penetrate metal foils. In 1898, Marie and Pierre Curie found that thorium had radioactive properties, and in quick succession they added polonium and radium to the list of radioactive elements. Marie Curie also gave the name to the process whereby uranium gives off rays: radioactivity. As the list of radioactive elements grew in confusing profusion, Rutherford and Frederick Soddy produced the theory of radioactive transformation through “decay” of one element to another. The concept of isotopes (a term coined by Soddy) also simplified the number of elements on the list. Rutherford utilized the alpha particles to investigate the structure of the atom, which revolutionized the model of the atom. In 1900, Paul Villard observed a third ray more powerful than X rays, called gamma rays, which were emitted by radioactive substances.
By the first decade of the twentieth century, the initial exploration of radioactivity had opened the door to the study of nuclear physics, which changed the very concept of the nature of the material world. In a series of papers published in 1914, Rutherford described the hypothesis of a new atomic model that included the proton as the nucleus of the atom. The Rutherford model of the atom gained prominence through the work of Niels Bohr. Bohr saved this new model of the atom by proposing a quantum theory, whereby the energy of the spinning electron emits energy only in specific quanta. This means that during stable orbits of the electron, there is no emission of radiation, but when the electron jumps from one orbit to another through increasing or decreasing energy of the atom, radiation is emitted. Furthermore, the quantum numbers for the electrons are whole numbers. Although this model of the atom was later referred to as the “Bohr atom,” credit must be given to Rutherford for providing the basic structure. The stage was set for scientists to investigate further the structure of the atom, a process that involved a multinational effort through the twentieth century. In the history of science, no other single revolution is comparable to the discovery of radioactivity.
Bibliography
Badash, Lawrence. “Becquerel’s Blunder.” Social Research 72 (Spring, 2005). This article, part of an issue devoted to “fruitful errors,” describes Becquerel’s discovery of radioactivity.
Broglie, Louis de. The Revolution in Physics: A Non-mathematical Survey of Quanta. Translated by Ralph W. Niemeyer. New York: Noonday Press, 1953. A highly recommended text for those seeking nontechnical information on quantum mechanics. Attempts to provide a popular explanation of the rapidly changing world of physics and makes the difficult subject of quantum mechanics accessible to the general reader.
Crowther, J. G. The Cavendish Laboratory, 1874-1974. New York: Science History Publications, 1974. Covers the history of the laboratory. Various chapters cover Joseph John Thomson’s early years at the laboratory, his initial work as director, his assistants and students, his work on the electron, and the later period of his life, through the end of World War I. In addition, two chapters cover his predecessor, Lord Rayleigh, and eight chapters discuss his successor, Ernest Rutherford.
Einstein, Albert, and Leopold Infeld. The Evolution of Physics: The Growth of Ideas from Early Concepts to Relativity and Quanta. 1938. Reprint. New York: Simon & Schuster, 1966. Probably one of the most accessible single volumes of history on the development of modern physics available to the general reader. Employs few technical terms, and no knowledge of mathematics is required. The sections on the decline of the mechanical view and on quanta are highly recommended.
Jammer, Max. The Conceptual Development of Quantum Mechanics. 2d ed. Los Angeles: Tomash, 1989. Traces both the physics and the conceptual framework of quantum theory. The sections covering the formative development of quantum theory are moderately accessible for the general reader.
Rayner-Canham, Marelene F., and Geoffrey W. Rayner-Canham. A Devotion to Their Science: Pioneer Women of Radioactivity. Philadelphia: Chemical Heritage Foundation, 2005. A collection of biographical essays on twenty-three women involved in atomic science research in the early part of the twentieth century, including Marie Curie as well as many lesser-known scientists whose stories are rarely told.
Romer, Alfred. The Restless Atom: The Awakening of Nuclear Physics. 1960. Reprint. Mineola, N.Y.: Dover, 1982. This standard text on the early days of nuclear physics is highly recommended. Romer makes the details of this part of history easily accessible.
Segrè, Emilio. From X-Rays to Quarks: Modern Physicists and Their Discoveries. San Francisco: W. H. Freeman, 1980. Segrè was one of a handful of physicists who participated directly in nuclear physics, received a Nobel Prize for his work, and wrote a number of popular accounts on the history of physics. The earlier sections of this volume cover the discoveries and theories of those who produced a coherent picture of the atom.