Henri Becquerel - Biographical Henri Becquerel The Nobel Prize in Physics 1903 Henri Becquerel, Pierre Curie, Marie Curie Share this: Henri Becquerel - Biographical Antoine Henri Becquerel was born in Paris on December 15, 1852, a member of a distinguished family of scholars and scientists. His father, Alexander Edmond Becquerel, was a Professor of Applied Physics and had done research on solar radiation and on phosphorescence, while his grandfather, Antoine César, had been a Fellow of the Royal Society and the inventor of an electrolytic method for extracting metals from their ores. He entered the Polytechnic in 1872, then the government department of Ponts-et-Chaussées in 1874, becoming ingénieur in 1877 and being promoted to ingénieur-en-chef in 1894. In 1888 he acquired the degree of docteur-ès-sciences.

From 1878 he had held an appointment as an Assistant at the Museum of Natural History, taking over from his father in the Chair of Applied Physics at the Conservatoire des Arts et Metiers. In 1892 he was appointed Professor of Applied Physics in the Department of Natural History at the Paris Museum. He became a Professor at the Polytechnic in 1895. Becquerel's earliest work was concerned with the plane polarization of light, with the phenomenon of phosphorescence and with the absorption of light by crystals (his doctorate thesis). He also worked on the subject of terrestrial magnetism. In 1896, his previous work was overshadowed by his discovery of the phenomenon of natural radioactivity. Following a discussion with Henri Poincaré on the radiation which had recently been discovered by Röntgen (X-rays) and which was accompanied by a type of phosphorescence in the vacuum tube, Becquerel decided to investigate whether there was any connection between X-rays and naturally occurring phosphorescence. He had inherited from his father a supply of uranium salts, which phosphoresce on exposure to light.

When the salts were placed near to a photographic plate covered with opaque paper, the plate was discovered to be fogged. The phenomenon was found to be common to all the uranium salts studied and was concluded to be a property of the uranium atom. Later, Becquerel showed that the rays emitted by uranium, which for a long time were named after their discoverer, caused gases to ionize and that they differed from X-rays in that they could be deflected by electric or magnetic fields. For his discovery of spontaneous radioactivity Becquerel was awarded half of the Nobel Prize for Physics in 1903, the other half being given to Pierre and Marie Curie for their study of the Becquerel radiation. Becquerel published his findings in many papers, principally in the Annales de Physique et de Chimie and the Comptes Rendus de l'Academie des Sciences. He was elected a member of the Academie des Sciences de France in 1889 and succeeded Berthelot as Life Secretary of that body. He was a member also of the Accademia dei Lincei and of the Royal Academy of Berlin, amongst others.

He was made an Officer of the Legion of Honour in 1900. He was married to Mlle. Janin, the daughter of a civil engineer. They had a son Jean, b. 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. From Nobel Lectures , Physics 1901-1921, Elsevier Publishing Company, Amsterdam, 1967 This autobiography/biography was written at the time of the award and first published in the book series Les Prix Nobel . It was later edited and republished in Nobel Lectures . To cite this document, always state the source as shown above. French physicist, and Nobel laureate (1852–1908)., Autograph manuscript (fragment). $ 4,975 / 4.500 € (35084) Becquerel writes research notes on molecular X- rays, electrolysis, ions, etc., which is part of Becquerel's own work related to radioactivity.

Becquerel writes in his hand scientific notes about ions, electrolysis, atoms, molecules, positive charges of the ions and how they react, he writes several long formulas, including: “e/e=l,n=rx10 to the power of 19,and then explains how e/u= 10 to the power of 7, 2x 1000…of the electrolysis v( S 10 to the power of 4 ), l/2000 of the atom dissolving middle body.” Manuscripts by Becquerel discussing his work on radioactivity are of great rarity. Becquerel whose experiments with uranium salts led to the discovery of spontaneous radioactivity; for this breakthrough he shared the 1903 Nobel Prize for Physics with Marie and Pierre Curie.. read more biography Antoine Henri Becquerel. The Nobel Prize in Physics Antoine Henri Becquerel The Nobel Prize in Physics 1903 biography (b. Dec. 15, 1852, Paris--d. Aug. 25, 1908, Le Croisic, Fr.), French physicist who discovered radioactivity through his investigations of uranium and other substances.

In 1903 he shared the Nobel Prize for Physics with Pierre and Marie Curie. (see also Index: physical science) He was a member of a scientific family extending through several generations, the most notable being his grandfather Antoine-Cesar Becquerel (1788-1878), his father, Alexandre-Edmond Becquerel (1820-91), and his son Jean Becquerel (1878-1953). Education and training. After his early schooling at the Lycee Louis-le-Grand, Henri received his formal scientific education at the Ecole Polytechnique (1872-74) and engineering training at the Ecole des Ponts et Chaussees (Bridges and Highways School; 1874-77). In addition to his teaching and research posts, Becquerel was for many years an engineer in the Department of Bridges and Highways, being appointed chief engineer in 1894. His first academic situation was in 1876 as assistant teacher at the Ecole Polytechnique, where in 1895 he succeeded to the chair of physics.

Concurrently, he was assistant naturalist to his father at the museum, where he also assumed the physics professorship upon his father's death. Electricity, magnetism, optical phenomena, and energy were major areas of physical investigation during the 19th century. For several years the young man's research was concerned with the rotation of plane-polarized light by magnetic fields, a subject opened by Michael Faraday and to which Henri's father had also contributed. Henri then concerned himself with infrared radiation, examining, among other things, the spectra of different phosphorescent crystals under infrared stimulation. Of particular significance, he extended the work of his father by studying the relation between absorption of light and emission of phosphorescence in some uranium compounds. (see also Index: electromagnetic radiation) By 1896 Henri was an accomplished and respected physicist--a member of the Academie des Sciences since 1889--but more important than his research thus far were his expertise with phosphorescent materials, his familiarity with uranium compounds, and his general skill in laboratory techniques, including photography. Together, these were to place the discovery of radioactivity within his reach. Systematic study of radiation.

At the end of 1895, Wilhelm Rontgen discovered X-rays. Becquerel learned that the X-rays issued from the area of a glass vacuum tube made fluorescent when struck by a beam of cathode rays. He undertook to investigate whether there was some fundamental connection between this invisible radiation and visible light such that all luminescent materials, however stimulated, would also yield X-rays. To test this hypothesis, he placed phosphorescent crystals upon a photographic plate that had been wrapped in opaque paper so that only a penetrating radiation could reach the emulsion. He exposed his experimental arrangement to sunlight for several hours, thereby exciting the crystals in the customary manner. Upon development, the photographic plate revealed silhouettes of the mineral samples, and, in subsequent experiments, the image of a coin or metal cutout interposed between the crystal and paper wrapping. Becquerel reported this discovery to the Academie des Sciences at its session on February 24, 1896, noting that certain salts of uranium were particularly active. He thus confirmed his view that something very similar to X-rays was emitted by this luminescent substance at the same time it threw off visible radiation.

But the following week Becquerel learned that his uranium salts continued to eject penetrating radiation even when they were not made to phosphoresce by the ultraviolet in sunlight. To account for this novelty he postulated a long-lived form of invisible phosphorescence; when he shortly traced the activity to uranium metal, he interpreted it as a unique case of metallic phosphorescence. During 1896 Becquerel published seven papers on radioactivity, as Marie Curie later named the phenomenon; in 1897, only two papers; and in 1898, none. This was an index of both his and the scientific world's interest in the subject, for the period saw studies of numerous radiations (e.g., cathode rays, X-rays, Becquerel rays, "discharge rays," canal rays, radio waves, the visible spectrum, rays from glowworms, fireflies, and other luminescent materials), and Becquerel rays seemed not especially significant. The far more popular X-rays could take sharper shadow photographs and faster.

It required the extension in 1898 of radioactivity to another known element, thorium (by Gerhard Carl Schmidt and independently by Marie Curie), and the discovery of new radioactive materials, polonium and radium (by Pierre and Marie Curie and their colleague, Gustave Bemont), to awaken the world and Becquerel to the significance of his discovery. Further contributions. Returning to the field he had created, Becquerel made three more important contributions. One was to measure, in 1899 and 1900, the deflection of beta particles, a constituent of the radiation, in both electric and magnetic fields. From the charge to mass value thus obtained, he showed that the beta particle was the same as Joseph John Thomson's recently identified electron. Another discovery was the circumstance that the allegedly active substance in uranium, uranium X, lost its radiating ability in time, while the uranium, inactive when freshly prepared, regained its activity. When Ernest Rutherford and Frederick Soddy found similar decay and regeneration in thorium X and thorium, they were led to the transformation theory of radioactivity, which explained the phenomenon as a subatomic chemical change in which one element spontaneously transmutes into another.

Becquerel's last major achievement concerned the physiological effect of the radiation. Others may have noticed this before him, but his report in 1901 of the burn caused when he carried an active sample of the Curies' radium in his vest pocket inspired investigation by physicians, leading ultimately to medical use. For his discovery of radioactivity, Becquerel shared the 1903 Nobel Prize for Physics with the Curies; he was also honoured with other medals and memberships in foreign societies. His own Academy of Sciences elected him its president and one of its permanent secretaries. (L.Ba.) BIBLIOGRAPHY. There is no full-length biography of Becquerel in English. The article on him by Alfred Romer in the Dictionary of Scientific Biography, vol. 1 (1970), pp. 558-561, provides further details.

The Nobel Prize in Physics 1903 The Nobel Prize in Physics 1903 Henri Becquerel, Pierre Curie, Marie Curie Share this: The Nobel Prize in Physics 1903 Antoine Henri Becquerel Marie Curie, née Sklodowska Prize share: 1/4 The Nobel Prize in Physics 1903 was divided, one half awarded to Antoine Henri Becquerel "in recognition of the extraordinary services he has rendered by his discovery of spontaneous radioactivity", the other half jointly to Pierre Curie and Marie Curie, née Sklodowska "in recognition of the extraordinary services they have rendered by their joint researches on the radiation phenomena discovered by Professor Henri Becquerel". Photos: Copyright © The Nobel Foundation Share this: To cite this page MLA style: "The Nobel Prize in Physics 1903". Nobelprize.org. Nobel Media AB 2014. Web. 20 Jan 2017. < Pioneers: Henri Becquerel Henri Becquerel born Dec. 15, 1852, Paris, France died Aug.

25, 1908, Le Croisic Full name, Antoine-Henri Becquerel. French physicist who discovered radioactivity through his investigations of uranium and other substances. In 1903 he shared the Nobel Prize for Physics with Pierre and Marie Curie . He was a member of a scientific family extending through several generations, the most notable being his grandfather Antoine-Cesar Becquerel (1788ï¿½1878), his father, Alexandre-Edmond Becquerel (1820ï¿½91), and his son Jean Becquerel (1878ï¿½1953). After his early schooling at the Lycee Louis-le-Grand, Henri received his formal scientific education at the Ecole Polytechnique (1872ï¿½74) and engineering training at the Ecole des Ponts et Chaussï¿½es (Bridges and Highways School; 1874ï¿½77). In addition to his teaching and research posts, Becquerel was for many years an engineer in the Department of Bridges and Highways, being appointed chief engineer in 1894.

His first academic situation was in 1876 as assistant teacher at the ï¿½cole Polytechnique, where in 1895 he succeeded to the chair of physics. Concurrently, he was assistant naturalist to his father at the museum, where he also assumed the physics professorship upon his father's death. Electricity, magnetism, optical phenomena, and energy were major areas of physical investigation during the 19th century. For several years the young man's research was concerned with the rotation of plane-polarized light by magnetic fields, a subject opened by Michael Faraday and to which Henri's father had also contributed. Henri then concerned himself with infrared radiation, examining, among other things, the spectra of different phosphorescent crystals under infrared stimulation. Of particular significance, he extended the work of his father by studying the relation between absorption of light and emission of phosphorescence in some uranium compounds.

By 1896 Henri was an accomplished and respected physicistï¿½a member of the Academie des Sciences since 1889ï¿½but more important than his research thus far were his expertise with phosphorescent materials, his familiarity with uranium compounds, and his general skill in laboratory techniques, including photography. Together, these were to place the discovery of radioactivity within his reach. Returning to the field he had created, Becquerel made three more important contributions. One was to measure, in 1899 and 1900, the deflection of beta particles, which are a constituent of the radiation in both electric and magnetic fields. From the charge to mass value thus obtained, he showed that the beta particle was the same as Joseph John Thomson's recently identified electron. Another discovery was the circumstance that the allegedly active substance in uranium, uranium X, lost its radiating ability in time, while the uranium, though inactive when freshly prepared, eventually regained its lost radioactivity.

When Ernest Rutherford and Frederick Soddy found similar decay and regeneration in thorium X and thorium, they were led to the transformation theory of radioactivity, which explained the phenomenon as a subatomic chemical change in which one element spontaneously transmutes into another. Becquerel's last major achievement concerned the physiological effect of the radiation. Others may have noticed this before him, but his report in 1901 of the burn caused when he carried an active sample of the Curies' radium in his vest pocket inspired investigation by physicians, leading ultimately to medical use. For his discovery of radioactivity, Becquerel shared the 1903 Nobel Prize for Physics with the Curies; he was also honoured with other medals and memberships in foreign societies. His own Academy of Sciences elected him its president and one of its permanent secretaries.

Antoine-Henri Becquerel For anything and everything on science from India Antoine-Henri Becquerel Dr V B Kamble Antoine-Henri Becquerel (1852-1908) is known for his discovery of radioactivity, for which he received the Nobel Prize for Physics jointly with Marie Curie (1897-1934) and Pierre Curie (1859-1906) in 1903 and the contributions he made to that field. He was a member of the Academy of Sciences, became its President, and was elected to the far more influential post of permanent Secretary. He held three chairs of Physics in Paris - at the Museum of Natural History, at the cole Polytechnique,and at the Conservatoire National des Arts et Méésartiers' - and attained high rank as an engineer in the National Administration of Bridges and Highways. Henri's father, Alexandre-Edmond Becquerel, and his grandfather, Antoine César becquerel,were renowned physicists, both members of the Academy of Sciences and each in his turn professor of Physics at the Muserum of Natural History.

Henri Becquerel was born on December 15, 1852, and was educated at the Lycee Louis-le-Grand,Ecolésar Polytechnique (1872-1874) and at the Ecolésar des Ponts et Chaussees (1874-1877), where he received his engineering training. On leaving the Polytechnique, he married Lucie-Zoe-Marie Jamin, daughter of J.C. Jamin, academician and professor of Physics in the Faculty of Sciences in Paris. Before the end of his schooling, he had begun both his private research and his teaching career at the Polytechnique.His wife died in March 1878, a few weeks after the birth of their son Jean.Becquerel succeeded to the post of his father at the Museum, and from then on,his professional life was shared among the Museum, the Polytechnique, and the Ponts et Chaussees. Becquerel's early research was almost exclusively in optics.His first extensive investigations (1875-1882) dealt with the rotation of plane-polarised light by magnetic fields.

He next turned to infra-red spectra, making visual observations by means of the light released from certain phosphorescent crystals under infra-red illumination. He then studied the absorption of light in crystals.With these researches, Becquerel obtained his doctorate from the Faculty of Sciences of Paris (1888) and election to the Academy of Sciences (1889). In 1890, he married his second wife. Following the death of his father in 1891,he succeeded in the following year to his father's two chairs of Physics at the Conservatoire National des Arts et Métiers and at the Museum. Thus, in the beginning of 1896, at the age of forty three, Becquerely was established in the rank and responsibility, his years of active research behind him and all that for which he is now remembered still undone! There are few scientific discoveries whose circumstances are known as minutely as those around the almost accidental finding of radioactivity. On January 7, 1896, the great French mathematician Jules-Henri Poincare (1854-1912) received a letter containing several astonishing photographs of the bones in someone's hand.

The bones belonged to Wilhelm Conrad Rööntgen (1845-1923), a scientist Poincare had never visited. The letter explained that the pictures had been taken with the aid of a new discovery, X-rays that Ròöntgen had turned up the previous month, and that he was publicizing his findings by mailing off prints all over Europe. Publicized they were: The photographs created a sensation across the globe(fig.3). Within three weeks, little Eddie McCarthy of Dartmouth, New Hampshire, became a local celebrity when his broken arm was set by physicians armed with X-rays images of the fracture(fig.4). It is easy to imagine Poincare's amazement-photographs of the inside of a human being! -and he quickly asked two local doctors if they could duplicate Röntgen's work. On January 20, they showed their own X-ray photographs to the assembled members of the French Academie des Sciences. The reaction was immediate and extreme. In the next fortnight, five members of the Academie presented papers on the new phenomenon.

Antoine-Henri Becquerel (1852-1908), too, was sitting in the audience when the X-ray photographs were shown. He was fascinated by the strange ghostly images and the mysterious emanations that produced them.Both he and his father had studied the phenomenon of phosphorescence-the museum laboratory was filled with lumps of stone and wood that shone in the dark. The glow of X-ray emission put Becquerel in mind of the light in his study; although he had not done much active research in the last few years, he thought immediately of putting some phosphorescent rock on photographic paper to see if it would darken it in the same way as one of Röntgen's X-ray sources. It would not be all that much work. Born on December 15, 1852, Becquerel was the third in the line of Becquerel who held the chair of applied physics at what is today called the National Museum of Natural History in Paris. Like his grand father Antoine-Cesar Becquerel, and father Alexandre-Edmond Becquerel, before him, he was a member of the French Academy of Sciences and attended its weekly meetings.

During the meeting of January 20, 1896, he felt that the X-rays appeared to emanate from the area of a glass vacuum tube made fluorescent when struck by a beam of cathode rays. Poincare wondered aloud if such radiation was emitted by other luminescent bodies. Becquerel was immediately challenged by this question. In fact, he was ideally suited to answer it. Not only was he expert in the investigation of various luminescent effects, a common activity in physical laboratories of the 19th century, but he had studied the phosphorescence of some uranium compounds in particular. He also was skilled in laboratory applications of photography. And, like most physicists, he sought a better understanding of the nature of matter, so perhaps the mechanics of phosphorescence would bring him closer to reaching this final, philosophical goal. What is Radioactivity? Imagine that you are holding a water melon in your hands. All of a sudden, for no apparent reason, one of its seeds comes flying out through the thick skin. At the same time, you find that the water melon has turned into a musk melon.

Before you realise what happened, the musk melon throws out a seed and turns into an apple.As you are looking at the apple wondering to bite into it or not, a seed shoots out of it, and now what you have in your hand is an orange. By the time you try comprehend this unbelievable chain of event, the orange throws out a seed and becomes a emon. Surely, you would not like to eat a lemon, so you wait for it to turn into a berry or into a grape. You keep waiting, but nothing happens. The lemon remains a lemon. You may think that may be the a magician is trying to keep you awaiting from eating, or that there is a hitherto unknown power which is responsible for the entire chain of events. Fortunately, we never find one fruit changing into another kind of fruit the way it is described here.However, you may like to note that a very similar process is called Radioactivity. Atoms are the smallest constituents that make up of elements, and hence all matter. At the centre of each atom, there is a much smaller nucleus that contains even tinier particles called Protons and Neutrons.

The nucleus of a "Radioactive"atom - throw out one or more of these tinier articles, sometime particles other than proton or neutron thereby changing into a different element, or sometimes electromagnetic radiation. Such a nucleus is said to decay, or break apart when the decay of a nucleus occur. One type of atom is changed into a different type., and hence one element into another. and will consider his watch to be slow! An expert on uranium phosphorescence: In the second half of the 19th century, Henri's father, Alexandre-Edmond Becquerel (1820-1891), was the leading authority in Europe on the subject of the phosphorescence of solids. It was an important field, made prominent by Robert Wilhelm Bunsen's (1811-1899) and Gustav Robert Kirchhoff's (1824-1887) recent spectroscopic analyses. Incidentally, "Fluorescence" is defined as the emission of light only during stimulation by external radiation. "Phosphorescence" persists after the external radiation ceases. "Luminescence" is the umbrella term.

Edmond was drawn to the investigation of uranium salts because of their exceptionally bright phosphorescence and their interesting spectra. One of his contributions was to show that the uranic series of salts is phosphorescent and that the uranous series is not.His son, Henri, began publishing on phosphorescence in 1883, and wrote twenty papers on this and related areas of study over the next 13 years, being attracted especially to the effects of infrared radiations. Like his father, Henri was fascinated by uranium salts, and he examined their absorption bands in both infrared and visible regions. Although uranium and its compounds interested the Becquerels, the study of these substances remained in something of a scientific backwater throughout the 19th century. Uranium had been discovered in 1789 by a German analytical chemist, Martin Klaproth, while he had been examining pitchblende from Saxony. Its name was chosen in honor of William Herschel's discovery of the planet Uranus in 1781 (a practice continued in the 20th century with the naming of neptunium and plutonium).

Not until 1841, however, was it recognized that Klaproth had obtained only the oxide. Eugene Peligot, a noted French chemist,then succeeded in separating the metal. Attention was again directed to uranium when Dmitri Ivanovich Mendeleev (1834-1907) formulated his periodic table in 1869 and showed it to be the heaviest element. But in an age of burgeoning chemical production, few applications for it were found. Compounds were tried as toning agents in photography, as dyes or stains for leather and wool and as mordants for silk and wool, and attempts were made with the metal to form an alloy with steel. The greatest use was in the ceramic and glass industries, in which uranium was valued for making coloured glazes and coloured clear glass. By varying the percentage of the salt used, one could get yellow, orange, brown, green or black. Photography entered the laboratory around the middle of the 19th century, being used to complement the microscope, telescope and balloon (for aerial photography),and to capture events such as sound waves, flying bullets, drop splashes, the motion of animals and lightning.

Röntgen's encounter with X-rays, which evoked tremendous public interest, relied heavily on photography for its fame. By far the greatest scientific use of this tool came in the century's last two decades,which suggests the impact of dry, gelatin emulsion plates. By 1896 Becquerel would probably have had at his disposal dry photographic plates of relatively good quality, uniform emulsion and long shelf life. Luminescence, uranium, photography Becquerel was in the right place at the right time. But he still might have failed to recognizes radioactivity as a phenomenon separate from phosphorescence if he had not been an accomplished physicist (Figure). Why does an apple remain an apple? Most atoms are not radio active, fortunately. Their neuclei are "stable",i.e. they do not decay. This is why an ordinary object, such as an apple or a watermelon with millions and millions of atoms with stable neuclei, always remains the same. Incidentally, we call a radioactive nucleus unstable because it can decay. When it does decay, both the number of protons and neutrons can change. Will the resulting nucleus be stable? Well, it may be stable or it too may be radioactive.

If it is radio active, it may be further decay to form yet another new nucleus, which could be radioactive as well. This is how a "decay series" could occur. Each kind of chemical element in the series changes into the next kind. Ultimately, the series may end with an element such as lead, i.e. not radio active. The atoms in this element are stable, they do not decay. Thus after a sufficiently long time one may find that radium or uranium has completely changed into lead! A model of scientific method: Becquerel's working hypothesis was that a body had to luminesce to emit penetrating radiation such as Röö;ntgen had found. His technique was to wrap a photographic plate in light tight black paper, position the mineral on the plate, and leave the experiment on his window sill where sunlight would stimulate the mineral to glow. At a meeting of the Academy of Sciences on 24 February 1896, he claimed success, reporting that several materials in particular, phosphorescent crystals of potassium uranyl sulfate emitted rays that penetrated thick black paper and exposed the photographic plate. This exposure was little more than a smudge.

To refine the results and to make them more attractive to others Becquerel also placed coins and other thin, metallic objects under the crystals, producing interesting silhouettes and showing their penetrating power. It must, however,be stated that X-rays, which produced far sharper photographic images in less time were overwhelmingly more popular. On Wednesday and Thursday, 26 and 27 February, 1896, Becquerel prepared several arrays of crystals and photographic plates. The Parisian winter, however, brought half a week of overcast skies, forcing Becquerel to postpone the experiments;he felt that he needed strong sunlight. The plates rested in a dark drawer until Sunday, 1 March, when Becquerel developed them, "expecting to find very weak images. To the contrary", he wrote in his memoirs, "the silhouettes appeared with great intensity". The following day, on 2 March 1896, Becquerel reported to the Academy of Sciences that the potassium uranium sulfate crystals could be stimulated to emit the new rays by diffuse daylight hrough a thin cloud cover, as well as by reflected and refracted direct sunlight. He also described using different thicknesses of copper foil to examine the absorption of the rays.

But the most astounding result that Becquerel offered was that stimulation of the crystals by sunlight immediately before or during the experiment was apparently not necessarry. The Uranium, it seemed, was spitting out X-rays all by itself. This, too, was not entirely correct. In fact, the lump of potassium uranyl sulfate was emitting a whole spectrum of radiation, of which only a small portion was X-rays. Nonetheless, the discovery caused a sensation, in part because it was so easy to duplicate. Almost every laboratory in the world had construction paper,photographic plates, and chunks of uranium ore. Within weeks, scientists across the Continent were looking in astonishment at the blurred black patches on their photographs making Becquerel a celebrity (Figure). Within weeks, news of Becquerel's findings had spread to Germany, Great Britain, Italy, and the United States, further exciting researchers already stirred by the discovery of X-rays. Tests of the two phenomena were often conducted on the same workbench. The consequences of each discovery, however, were far different. X-rays were found to be simply pulses of light light of an intensity and power never before seen, but light nonetheless.

Radioactivity, on the other hand, was something entirely new, something that did not fit anywhere. The existence of radioactivity metal that somehow shot out energy! was a direct attack on the most ardent beliefs of Becquerel and his colleagues. When the strange behaviour of uranium was first noted, Becquerel wrote in his memoirs, "There was no reason to presume that the phenomenon was [anything but] a new example of a known type of energy transformation. Contrary to every expectation, the first experiments demonstrated the existence of an apparently spontaneous production of energy" . They had spent many years, those nineteenth century scientists, establishing the law of conservation of energy: Energy was neither created not destroyed. But every single piece of uranium seemed of its own accord to produce radiation that fogged photographic plates, electrified gases, and sometimes even burned physicists and the energy needed to do these things evidently came from no place at all. The metal just sat there, its atoms quietly working away, continuously beaming out penetrating rays in seeming disregard for the conservation of energy.

A page from the doctoral thesis of Marie Curie (1903) Marie Curie's representation of alpha, beta and gamma rays in a magnetic field from a radioactive material placed in a narrow but deep cavity in a block of lead. The magnetic field is applied in a direction perpendicular to and out of the plane of the paper. In the absence of electric and magnetic fields, the rays would emerge as a thin vertical beam. The alpha particles being positively charged and relatively heavy, would be slightly deflected to the right. The beta particles, being negatively charged and light, would be deviated to a greater extent to the left, whereas the gamma rays, carrying no electric charge, would not be deflected at all. What prompted Becquerel to develop the plates? But why had Becquerel bothered to develop those plates, which he thought were faintly exposed at best? His behavior has been explained as thoroughness: Jean Becquerel has suggested that his father planned to resume his experiments and wished to use fresh plates, so why to develop the old ones anyway? The explanation (proffered by G.E.M.

Jauncey in a 1946 paper in the American Journal of Physics) is "impatience after awaiting four days for the sun to shine". Yet other reasons, suggested, are "simple thrift or an overriding curiosity". We can dismiss the belief that Becquerel planned to resume his experiments on that Sunday: Meteorological records indicate that the day was less sunny than the average of the ceding four days A better explanation for Becquerel's activity is that he wanted to have sufficient material to report at the next day's session of the academy. In previous experiments he had already found, or so he believed, that weak illumination triggered his crystals somewhat. Perhaps he thought that these newly prepared plates had been exposed to some diffuse daylight, if not a short period of sunlight, before he placed them in the dark drawer. Thus, even if he could not describe many additional experiments, he might furnish evidence of the connection between the intensity of the photographic image and the intensity and duration of phosphorescence.

Another page from Marie Curie's doctoral thesis describing the set-up for measuring the ionisation power of "uranium rays" The method employed consists in measuring the conductivity acquired by air under the action of radioactive bodies; this method possesses the advantage of being rapid and of furnishing figures which are comparable. The apparatus employed by me for the purpose consists essentially of a plate condenser, AB (Figure 1). The active body, finely powdered, is spread over the plate B, making the air between the plates a conductor. In order to measure the conductivity, the plate B is raised to a high potential by connecting it with one pole of a battery of small accumulators. P, of which the other pole is connected to earth. The plate A being maintained at the potential of the earth by the connection CD,an electric current is set up between the two plates. The potential of plate A is recorded by an electrometer, E. If the earth connection be broken at C, the plate A becomes charged, and this charge causes a deflection of the electrometer. The velocity of the deflection is proportional to the intensity of the current, and serves to measure the latter.

But a preferable method of measurement is that of complensating the charge of plate A, so as to cause no deflection of the electrometer. The charges in question are extremely weak; they may be compensated by means of a quartz electric balance, Q, one sheath of which is connected to plate A and other to the earth. The quartz lamina is subjected to known tension, produced by placing weights in a plate,T; the tension is produced progressively, and has the effect of generating progressively a known quantity of electricity during the time observed. The operation can be so regulated that, at each instant, there is compensation between the quantity of electricity that traverses the condenser and that of the opposite kind furnished by the quartz. In this way, the quantity of electricity passing through the condenser for a given time, i.e., the intesity of the current, can be measured in absolute units. The measurement is independent of the sensitiveness of the electrometer. (Source Resonance, March 2001) (fig.6).

That he found the plates as blackened as they would have been had the crystals phosphoresced continuously, and that he recognized the significance of his surprising observation, shows that the discovery of radioactivity was not simply a happy accident but also a product of genuine scientific talent. Becquerel's example is comforting to us: His genius emerged because he mistakenly believed in a connection between the penetrating rays and phosphorescence, and because he felt compelled to speak at the academy's meeting. Though a major step, this event does not deserve to be called the discovery of radioactivity. The discovery was a process, not an instantaneous occurrence, for even at this point Becquerel had not sufficiently localized the phenomenon. No doubt Becquerel was a skilled and ingenious experimenter. However, in this early research he was not sufficiently meticulous to exclude extraneous influences and to see that some of his experimental results could bear more than one explanation. Thus, he often concluded that his experiments proved uranium rays to posses a certain physical property, only to have it shown later that the effect was due to another cause. Indeed, his investigations are particularly interesting for their many false trails, unreproducible results and misinterpreted effects.

Yet,his erroneous conclusions inexorably led him to further experiments, which often revealed the true nature of the phenomenon. This uneven progress is perhaps the most striking facet in the story of the discovery of radioactivity. But it must be understood that few scientists are able to avoid false trails. He recognized that the next step must be to determine if any light at all was necessary to stimulate the crystals. Working in a dark room, he placed different minerals atop photographic plates in an opaque cardboard box. When developed five hours later, the plates showed strong images in samples in which the crystals lay directly on the emulsion and less intense images in those in which the crystals were separated from the emulsion by sheets of aluminum and glass. Besides showing attenuation, the samples involving aluminum and glass also indicated that chemical action was not the explanation for the photographic smudges. Nor could the smudges result from the luminous radiation, because the phosphorescence of uranium salts is perceptible only for about 0.01 second, too short a time to expose a plate.Becqurel therefore suggested that phosphorescent bodies might give off an invisible emission that lasts much longer than the visible radiation.

Even before Rö;ntgen's discovery of X-ray, it had become almost a standard procedure for scientists exploring various types of radiation to perform some of the experiments that Rö;ntgen conducted to determine the properties of X-rays. Becquerel followed suit, as was only logical, because he believed that his own rays were similar to X-rays. He only had to substitute a layer of uranium salts for a cathode-ray tube, for example, to show that the separate gold leaves of an electroscope were made to fall. Having established this electrical property, he next examined whether the rays were reflected and refracted and he claimed they were. This conclusion, however, would be corrected by Rutherford some three years later. Through March and the succeeding months of 1896, Becquerel found that those crystals kept in darkness retained their ability to expose a photographic plate. Surely, he felt, this was a remarkable example of long-lived phosphorescence. But he was at a loss to explain the equally intense images produced by non-phosphorescent uranous sulfate. This discovery led him on a new path of investigation.

Since uranium nitrate ceases to luminesce when dissolved or melted in its water of crystalization, Becquerel, in darkness, heated a crystal in a sealed glass tube, protecting it even from the light of the alcohol flame. He then allowed it to recrystallize in darkness. All phosphorescence had been destroyed in this process, yet the salt still produced results on a photographic plate as strong as crystals exposed to light. Indeed, Becquerel admitted the anomalous behaviour of his samples: All salts of uranium emitted the invisible radiation, while other phosphorescent bodies did not. Finally, he tried a disk of pure uranium metal and found that it produced penetrating radiation three to four times as intense as that he had first seen with potassium uranyl sulfate. With this last announcement, on May 18, 1986, Becquerel's discovery of radioactivity was complete, although he continued with ionization studies of his penetrating radiation until the following spring. The new rays emerged from the element uranium, and with the implicit consequence that this was an atomic phenomenon, it may be said that the process of the discovery of radioactivity was essentially over.

It was a process that took several months, notable for a number of conclusions that were later overturned! Enter Marie and Pierre Curie Marie Curie (1867-1934) leaped into this exciting new field. She soon discovered at roughly the same time that Becquerel and Ernest Rutherford (1871-1937)(fig8) did that the radiations given off by uranium were composed of more than one type. Some rays were bent one way by a magnetic field; others were bent another way. Rutherford named the positively charged rays alpha rays and the negatively charged ones beta rays (also known as alpha particles and beta particles). Exactly what these rays or particles were composed of, no one knew, but by 1898 Marie Curie suggested a name for these radiations radioactivity and that is the name that stuck. And in 1900, Paul Ulrich Villard discovered a third, unusually penetrating type of ray in radioactive radiation, one that did not bend at all n a magnetic field, which he named the gamma ray. The use of Greek letters to name these rays simply meant that their identity was unknown, as with the X in X-ray.

The Law of Exponential Decay Rutherfod and Soddy observed in 1902 that the activity of a radioactive element was diminishing in an exponential or (logarithmic) manner. This implied that the rate of decay of an active species, that is, the number of atoms that disintegrate in a unit interval of time, is proportional to the total number of atoms of that species present at that time. If we suppose that at a given instant, there are N atoms present of a particular radioelement, the rate of disintegration is represented by dN/dt. Since the rate of disintegration is proportional to the total number of atoms N, the relationship between the two, following methods of simple calculus, can be written as - dN/dt = N where l is is a constant which Rutherford and Soddy called the "radioactive constant". It is now referred to as the disintegration constant or the decay constant of the element under consideration. The negative sign is due to the fact that the number of atoms of the radioactive element decreases with time, and hence the rate dN/dt is a negative quantity.

The value of l depends on the property of a given radioelement and is independent of the physical condition or state of chemical combination. In an equivalent exponential form, the above equation yields the result, N t = N 0 e - lt where N 0 is the number of atoms present at any arbitrary zero time and N t is the number remaining after the lapse of a further time t. Another constant introduced by Rutherfod in 1904, called the "half-life" is the time required for the radioactivity of a given amount of the element to decay to half its initial value, that is, when half of the N0 atoms present at the zero time have decayed. Marie Sklodowska, a Polish girl came to Paris at the Sorbonne University to study physics and mathematics and qualified with honours and distinction. She married Pierre Curie (1859-1906) of the same university in 1895. Pierre was already famous for his discovery of piezo electricity - a property shown by some crystals such as quartz of developing an electrical voltage between opposite ends when subjected to pressure. Marie Curie used the discovery of her husband (see Box) to measure radioactivity.

Radioactive rays, like X rays, ionized any gas they passed through (including air) making it capable of conducting electricity. She found that she could measure the current so conducted with a galvanometer and offset it with the potential of a crystal under pressure. By measuring the amount of pressure it took to balance the current, she could obtain the reading of the intensity of the radioactivity. She systematically tested radioactive salts and succeeded in showing that the degree of radioactivity was in proportion to the amount of uranium in the radioactive material thereby narrowing the source of the radioactivity in her samples down to uranium. Then in 1898 she made yet another find: the heavy element thorium was also radioactive. It was already known that natural pitchblende is three or four times more active than uranium. Even more interesting is the fact that as Marie was working to separate uranium out of pitchblende, she found that the residues she produced had a much higher measurement of radioactivity than the uranium content alone could account for. Since the other minerals present in the ore were not radioactive, that could mean only one thing. Some other radioactive element, in amounts too small to detect, must also be present!

By this time, Marie's work had developed so much potential that her husband Pierre joined her to help with the backbreaking, tedious work of crystallizing the elements from the ores. Though himself a fine scientist with a successful career, he set his own work aside and spent the remaining seven years of his life assisting her, recognizing both her extraordinary gifts as a scientist and the importance of the path she was following. By July 1898 the two had succeeded. Working together, they had isolated a tiny amount of powder from the uranium ore from the fraction that contained bismuth. It was a new element, never before detected, with a level of radioactivity 400 times higher than uranium. They named the new element polonium, after Marie's home country. But something still seemed strange. The ore still gave off more radioactivity even than the uranium and polonium combined could account for. There must still be something else. In December 1898 they found the answer: another, even more radioactive element obtained from the fraction that contained barium which was 900 times more active than uranium. This one they named radium (from Latin radius meaning ray).

Marie and Pierre could not really offer a good description of new element radium because the amount they were able to derive from the ore they had was so minuscule. They could measure its radiations, and Eugene Demarcay, a specialist in elemental line spectra, was able to provide the spectral characteristics. (Different elements give off different wavelengths of electromagnetic radiation or light, and these can be observed as discrete lines.) The next project was to produce a large enough quantity of radium that they could weigh it and measure it and see it. For this, they required a much bigger laboratory and financial resources which Sorbonne University could not provide. Undaunted by the circumstances, they set to work in a make-shift laboratory housed in a neighbouring abandoned court-yard. Through the courtesy of the Academy of Sciences, Vienna, they managed at a reasonable cost, stacks of the required ore pitchblende. The new laboratory was damp with a leaky glass roof, walls made of card-boards, a few tables knocked together as the work tables, a gas stove and no exhaust to remove noxious fumes arising from the work upto 20 kg of the ore every day.

It was a back breaking, hazardous and almost suicidal adventure with no help coming from any quarters. They spent their life savings to obtain large masses of waste ore from a nearby mine, and they began the monumental task. They spent four years, during which Marie lost 5 pounds, purifying and repurifying the ore into small amounts of radium, say, about 0.1 gram. Marie Curie wrote her doctoral dissertation on the subject in 1903, for which she, Pierre and Henri Becquerel shared the Nobel Prize in physics that year. In 1906, two years after receiving an appointment as professor of physics at the Sorbonne, Pierre Curie was run over by a horse-drawn truck at the age of 47. Marie was appointed in his place and she became the first woman to teach physics at the Sorbonne. Eight years after Pierre's death (1914), she received another Nobel for her discovery of two new elements, viz. Polonium and Radium, this time in chemistry and this time alone, Pierre - her partner and collaborator - no longer at her side.

Years later, in 1935 to be precise, their daughter Irene and her husband Frederic Joliot-Curie - the second husband and wife team - were awarded the Nobel Prize in chemistry for their discovery of artificial radioactivity. Nobel Prizes awarded for work with radioactivity The discovery of radioactivity brought about a revolution in our conceptiual understanding of the matter and found applications various fields of human activity. Here is a list of Nobel Prizes awarded for work with radioactivity. 1903

Question: Henri Becquerel shared a Nobel prize for his work in discovering what?
Answer: Radioactivity