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ScienceWeek
RADIOACTIVITY
HENRI BECQUEREL (1852-1908): RADIOACTIVITY AND X-RAYS
In 1912, the eminent British scientist Ernest Rutherford (1871-1937) succeeded for the first time in obtaining convincing evidence that atomic nuclei really exist. However, the history of our knowledge concerning atomic nuclei begins earlier. The nuclear chronicle should actually begin with 1896. This starting point was marked by a scientific error, or, to be more precise, by an incorrect scientific hypothesis.
The question at hand concerned the nature of the then mysterious x-rays discovered just before (1895) by the German scientist Wilhelm Roentgen (1845-1923). Men of science in all countries were then under the impression of this discovery. Roentgen's work was subjected to careful study and discussion. The French scientist Henri Becquerel (1852-1908) took note of Roentgen's remark that the invisible X-rays he had discovered emerge from the end of a glass tube that glows with a yellowish green light which resembles the light of fluorescent substances. Both the yellowish green glow and the x-rays come out of the same spot of the glass tube. This was not fortuitous. In the tube with which Roentgen performed his investigations, the production of x-rays was always accompanied by a yellowish green illumination of the glass.
Becquerel had spent a long time in the study of various fluorescent materials which under the action of sunlight begin to radiate their own peculiar light. The idea that stimulated Becquerel's experiments was simple: is not fluorescence the cause of x-rays? Maybe x-rays exist whenever there is fluorescence. Now, in the light ot our knowledge concerning the constitution of the atom and the nature of x-rays, this idea seems absurd, but at that time, when the nature of these rays was unknown, this assumption appeared quite natural.
Becquerel was, of course, just lucky. It was by sheer accident that for the fluorescent material he took one of the uranium salts, the double sulfate of uranium and potassium. This circumstance predetermined the success of the experiment which was extremely simple and amounted to the following:
A photographic plate was carefully wrapped in black paper that did not pass visible rays. Then the uranium potassium sulfate was placed on the paper. The plate was then placed in bright sunlight. Several hours later it was developed with all possible precaution. A dark spot was detected on the plate and in form resembled the silhouette of the fluorescent material. Becquerel performed a series of control experiments and showed that this darkening arose from the action on the photographic plate of rays coming from the uranium crystals and passing through the black paper that is impenetrable to the sun's light.
At first Becquerel did not doubt that these were the x-rays. But he soon saw that he was mistaken. During these experiments, one of the days happened to be overcast and the uranium salt was hardly at all fluorescent. Assuming the experiment to be unsuccessful, he put the plate with the uranium salt back into the drawer of the case where it remained several days. Before his next experiment he developed this plate, since he was not sure that it was good any longer. To his surprise he saw a dark spot on the plate that was the image of the salt; the intensity of this image was exceptionally great. But in the dark case the salt had not fluoresced. Hence, fluorescence had nothing to do with it: there was something that affected the plate without fluorescence.
It was obvious that Becquerel had encountered some kind of new rays, and very soon it was established that these rays were due to uranium. Only such fluorescent materials as contained uranium affected a photographic plate, and a plate was affected by any of the uranium salts. But the strongest action was that produced by uranium itself.
The rays discovered by Becquerel resemble to some extent Roentgen's rays. They act on a photographic plate, and pass through black paper and thin layers of metal. However, these rays differ greatly. X-rays arise during an electric discharge in a highly rarefied gas. The pressure of the gas must be of the order of a millionth part of atmospheric pressure. A very high voltage (tens of kilovolts) must be applied to the electrodes before a discharge takes place. In these conditions, the x-rays are produced regardless of the nature ot the gas in the x-ray tube and also of the substance of the electrodes.
Becquerel's rays do not require any electric potential, either large or small. And no rarefied gas is necessary. X-rays appear only in the presence of an electric discharge, while Becquerel's rays radiate continuously and at all times."
Adapted from: M. Korsunsky: The Atomic Nucleus. Moscow, 1958, p.7. Translated from the Russian by G. Yankovsky.
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MARIE CURIE (1867-1934)
The following points are made by Roger M. Macklis (Science 2002 295:1647):
1) With the possible exception of Albert Einstein, Marie Curie was the most famous scientist of her era and is almost certainly the most celebrated female scientist in history. Although known primarily for her discovery of radium, her true gift to science was her realization that radioactivity is an intrinsic atomic property of matter rather than the result of superficial chemical processes. She was one of the exceedingly rare Nobel laureates to win the prize twice (physics and chemistry). Her life will forever reflect dogged determination, unswerving devotion to work, political tenacity, and an optimistic belief is scientific positivism. On a more personal note, she has also come to symbolize a cautionary tale concerning the unfortunate difficulties encountered when a woman enters and succeeds dramatically and publicly in a sphere traditionally dominated by men.
2) Initially viewed as a mere research assistant "riding" on the coattails of her more talented husband Pierre, his death in 1906 confronted her with the need and the opportunity to both establish her own scientific identity and to insist, despite her critics, on her place in the annals of the dawning technological age. She succeeded brilliantly, although she paid a personal price for her temerity.
3) After the death of her husband, Curie, now a distraught widow at 38, resolved to carry on the work that had been so important to her and her husband. She was promoted, amid some grumbling, to her husband's old chair. She continued her work on the chemical purification and characterization of radium and its byproducts, but her colleagues noted she had lost the fire that had imbued her previous research. A clandestine affair with the physicist Paul Langevin (1872-1946), a married student of her dead husband's and 5 years her junior, apparently renewed her zeal for life, but legal action by Langevin's wife brought the affair to the scandal sheets. Then, in the midst of all of this, the Swedish Academy announced that Marie Curie had been awarded an unprecedented second Nobel Prize, this time in chemistry, for the discovery of radium.
4) Curie traveled to Stockholm to accept the 1911 prize, but the public scandal concerning her affair with Langevin followed her. That year, Curie collapsed both physically and psychologically, and her subsequent scientific career was devoted primarily to organizing a national radium institute. When Curie died in 1934, she became the first woman to be granted the great honor of perpetual interment at the Pantheon in Paris. A year after her death, her daughter Irene won the family's third Nobel Prize.
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THE CURIES AND URANIUM
In the rush to build industries and make profits from the application of scientific knowledge, one must remember that nature does not easily give up her secrets, and that such knowledge is often gained only by arduous efforts and dedicated lives. Here are two excerpts concerning the Curies and their work on uranium:
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On April 19, 1906, the 47-year-old Nobel laureate Pierre Curie was run over by an oversize horse-drawn wagon filled with bales of army uniforms. He was negotiating that tricky Parisian intersection where traffic from the Rue Dauphine, the Quai Conti, the Quai des Grand Augustins, and the Pont Neuf have created Gallic havoc for over a century. Curie had just quit a meeting of reform-minded university professors where he argued for legislation to improve the lot of junior faculty and to prevent laboratory accidents. He had planned to stop at his publisher's office on the Quai, but the office was shut because of a strike by equally reform-minded trade unionists. Absent-minded and somewhat radium-sick, he turned away in the spring rain, and was on his way to the library of the Institut when that 6-ton wagon rumbled down the bridge from the Ile de la Cite to crush his skull.
The death brought to an end two remarkably creative careers in physical science, his own and that of his wife, Maria Salomea Sklodowska -- known to the world as Madame Curie. She later recollected that on the Rue Dauphine, "I lost my beloved Pierre, and with him all hope and all support for the rest of my life." She was right: for although Madame Curie was to survive her husband until 1934, her contributions to science after his death were less than innovative; she turned her tough mind to the application of their discoveries, to teaching young scientists, and to construction of the Radium Institute which she turned into a world center of physical science.
The story of Pierre and Marie Curie is a tribute to a dazzling set of discoveries jointly made by a man and a woman of genius... Among the most memorable photographs is a late one of an intense Marie Curie on the balcony of her Institute behind the Ecole Normale. Her lined face looks forward into the future, her hands are scrumbled by the scars of radium; it's an image that sums up the hope and the harm of her discovery. She would have been pleased that she is shown overlooking the street that we now call the Rue Pierre et Marie Curie."
Adapted from: Gerald Weissmann: Darwin's Audubon: Science and the Liberal Imagination. Plenum 1998, p.81,85. More information at: http://www.amazon.com/exec/obidos/ASIN/0738205974/scienceweek
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ON PERSEVERANCE IN RESEARCH
The School of Physics could give us no suitable premises, but for lack of anything better, the Director permitted us to use an abandoned shed which had been in service as a dissecting room of the School of Medicine.
Yet it was in this miserable old shed that we passed the best and happiest years of our life, devoting our entire days to our work. Often I had to prepare our lunch in the shed, so as not to interrupt some particularly important operation. Sometimes I had to spend a whole day mixing a boiling mass with a heavy iron rod nearly as large as myself. I would be broken with fatigue at the day's end. Other days, on the contrary, the work would be a most minute and delicate fractional crystallization, in the effort to concentrate the radium.
Thus the months passed, and our efforts hardly interrupted by short vacations, brought forth more and more complete evidence. Our faith grew ever stronger, and our work being more and more known, we found means to get new quantities of raw material and to carry on some of our crude processes in a factory, allowing me to give more time to the delicate finishing treatment. At this stage I devoted myself especially to the purification of the radium, my husband being absorbed by the study of the physical properties of the rays emitted by the new substances.
It was only after treating one ton of pitchblende residues that I could get definite results. Indeed we know today that even in the best minerals there are not more than a few decigrams of radium in a ton of raw material.
At last the time came when the isolated substances showed all the characters of a pure chemical body. This body, the radium, gives a characteristic spectrum, and I was able to determine for it an atomic weight much higher than that of the barium. This was achieved in 1902. I then possessed one decigram of very pure radium chloride. It had taken me almost four years to produce the kind of evidence which chemical science demands, that radium is truly a new element. One year would probably have been enough for the same purpose, if reasonable means had been at my disposal.
Adapted from: Marie Curie: Pierre Curie. Published 1927. Transl. Charlotte and Vernon Kellogg.
Editor's note: Marie Curie (1867-1934) and her husband Pierre Curie (1859-1906) shared the Nobel Prize for Physics in 1903. Marie Curie also won the Nobel Prize for Chemistry in 1911. Three years after receiving the Nobel Prize, Pierre Curie died at the age of 47 in a traffic accident, run over by a horse-drawn vehicle. During her work in the shed, Marie Curie also had to care for her 5-year-old daughter Irene, later known as Irene Joliot-Curie. Irene and her husband Frederic Joliot shared the Nobel Prize in Chemistry in 1935. Marie Curie died at the age of 67 of a leukemia apparently caused by her exposure to high-energy radiation (her notebooks are apparently still too contaminated to handle). She died one year before her daughter was awarded the Nobel Prize. Despite their poverty, and the chance for obvious riches, the Curies refused to patent their radium isolation process. Concerning the patenting of the process, Marie Curie stated: "It would be impossible, it would be against the scientific spirit... Physicists should always publish their researches completely. If our discovery has a commercial future, that is a circumstance from which we should not profit. If radium is to be used in the treatment of disease, it is impossible for us to take advantage of that."
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GEORGE DE HEVESY (1885-1966)
George de Hevesy (also known as George von Hevesy) received the Nobel Prize in Chemistry in 1943 for his his work on the use of isotopes as tracers in the study of chemical and biological processes. It is interesting that Hevesy's first use of radioactive tracers in 1923 was hardly noticed by chemists and biologists at the time, but before long his methods became the foundation for enormous progress in chemical dynamics, biochemistry, and physiology. In 1923, Hevesy, prodded by Niels Bohr and working with Dirk Coster, also discovered the element hafnium.
The following points are made by J. Van Houten (J. Chem. Ed 2002 79:301):
1) George de Hevesy developed his interest in isotopes while working in the laboratory of Ernest Rutherford (1871-1937) in Manchester, England between 1910 and 1913, and with Frederic Paneth at the Vienna Institute of Radium Research from 1913 to 1915, where de Hevesy and Paneth carried out the first radioactive tracer research. Rutherford had already received the Nobel Prize in 1908 for his "investigations into the disintegration of the elements and the chemistry of radioactive substances".
2) Prior to going to work with Rutherford in 1910, de Hevesy studied at Budapest University in his native Hungary and at Berlin Technical University. After receiving his doctorate from the University of Freiburg im Breisgau in 1908, de Hevesy worked for two years as an assistant at the Institute of Physical Chemistry, Technical University of Switzerland, and briefly with Fritz Haber (1868-1934), who was then working on the catalytic synthesis of ammonia by what later came to be known as the "Haber process", and for which Haber received the Nobel Prize in 1918.
3) After serving in the Australia Hungarian army during World War I, de Hevesy went to Copenhagen in 1919 to join the Institute for Theoretical Physics headed by Niels Bohr (1885-1962). Bohr received the Nobel Prize in physics in 1922 for his well-known theory of atomic structure. Bohr and de Hevesy had worked simultaneously in Rutherford's lab in Manchester a decade earlier. It was, of course, Rutherford's famous alpha-particle scattering experiments, performed in 1909, that led to the original nuclear model of the atom and ultimately to the Bohr model.
4) de Hevesy pioneered the use of radioisotopes as tracers, a technique that continues today in investigations of chemical reactions as well as in physiological studies. In fact, de Hevesy himself appears to have been more interested in the uses of tracers in physiological studies than in mechanistic chemical investigations. For example, he was among the first to employ P32--labelled sodium phosphate injected into animals and humans to study the rate of incorporation of phosphorus from the blood stream into various tissues, organs, bones, and tooth enamel. He performed similar experiments with radio-labeled sodium, potassium, lead, bismuth, and thallium in plants and animals. He also employed stable nuclides. For example, using deuterium-enriched water provided by Harold Urey (1893-1981), de Hevesy found that fish and amphibians swimming in that water take up deuterium and come to equilibrium with their environment with respect to deuterium in about four hours, and that humans who drink D2O excrete deuterium in their urine in approximately 26 minutes.
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