A short history of nuclear science


  Radioactivity
  Nuclear reactivity
  Atomic power
  Pacific uses of nuclear energy

   Radioactivity

The first scientist who claimed the discovery of something named later radioactivity was Claude Niepce de Saint-Victor, who discovered many useful technics of photography. In 1867, Niepce de Saint-Victor showed that uranium salts could emit radiations for several months in the dark ; he explained that fact by heat. Let understand why : he knew that uranium are luminescent, and since light is correlated with heat (according all old physics theories), he deduced that heat contained in the uranyl salt was responsible of the darkening of the plate. Roentgen had discovered X-rays in 1895, and noticed that the radiation was able to react with baryum platinocyanide ; the interesting point is that he used photographic plates to detect X rays : the goal was to study the property of absorption of the radiations, the surprising result is that he obtained the image of his hand.
Henry Becquerel was the son of Edmond Becquerel, a scientist who made a lot of studies about luminescence, in fact he was using the works of old chemists ; Nicolas Lemery (1675) described the preparation of the Pierre de Bologne (Stone of Bologne) discovered by the italian Vinsenzo Casciarolo, which has the property to be luminescent in the darkness. But Edmond Becquerel made a systematic study of luminescent materials , especially uranyl salts and among them uranyl sulfate. You will find most of the papers of Edmond Becquerel in Annales de Chimie et de Physique (available in University of Arizona, Tucson). Henry Becquerel established a relation between Niepce de Saint-Victor observation and Roentgen works since he recognized in one of his paper published in the Comptes Rendus de l'Acadťmie des Sciences that Niepce de Saint-Victor gave a wrong intepretation of radiation emitted by uranyl salts. Henry Becquerel demonstrated that a uranyl salt emits radiations that have properties similar with that of X-rays.
It is now the Polish girl , Maria Sklodowska , who decided to identify the source of the radiations emitted by the uranyl salt , and successfully discovered that the main source of radiations comes from trace elements mixed with uranium. We may admit that nuclear science really born with the discovery of radium and polonium.

This science history taked into account works of people whose business was the study of Physics and Chemistry. But it is interesting to search traces of the knowledge of radioactivity in older papers. The first point is to notice that discovery of radioactivity by scientists has been possible because they worked with uranium minerals. As we know, pure uranium salts such as uranyl nitrate, uranyl sulfate, are weakly radioactive, but older preparations, at least three months, present a higher radioactivity, and minerals have a very intense radioactivity.
A pocket book about Lead (Le Plomb (Marc Lheraud) - Que sais-je ?) indicates that the use of lead as protection against radiations was known years ago by some alchemists who wore pieces of lead to protect the heart :

We have seen that the luminescence of uranyl salts has been the main fact that lead to the discovery of radioactivity. Let also consider the history of the element phosphore which has been discovered by Brandt. It appears that substances emitting light had years ago, and still to-day, a very fascinating power. Light is related with Life, and years ago some people thought that luminescent materials should own a proper life : a mineral life.

   Nuclear reactivity

With the discovery of radioactivity, scientists have quickly understood that radioactive materials emit energetical particles, and may be used as a source of energy. But we have to wait Otto Hahn for the big discovery : the fission of uranium induced by neutrons. at the end of 1938. While working jointly with Dr. Strassmann, Hahn discovered the fission of uranium and thorium and his first work on these subjects appeared on 6th January and 10th February, 1939, in Naturwissenschaften.

   Atomic power

World war II has motivated Germany and USA to develop research programs about the possibility of making atomic bombs. The Germany reserach program is described in the interesting book : The German Atomic Bomb: The History of Nuclear Research in Nazi Germany (1983) ISBN 0-306-80198-1 ; it emphasizes the challenge between theorists and experimentalists. The Manhattan project of USA is well known, scientists from several nations worked under the commandment of general Groves , and Oppenheimer for the scientific part. Scientists habe been divided in teams, each one dedicated to a specific part of the research, for example Seaborg work was to separate plutonium produced from the bombardment of uranyl nitrate with neutrons ; Enrico Fermi worked on the making of a nuclear reactor.
The goal was to make an atomic bomb, it has been reached. In 1945 Bombs have been tested in Hiroshima (U-235) and then in Nagasaky (Pu-239)
It was the beginning of the cold war. Few years later Sovietic scientists succeeded in making fission bombs, and few years after fusion bombs. England too, produced nuclear weapons tested in Australia, but we have to wait 1960 to hear about France atomic weapons. IsraŽl with some technical support from France produced around 200 nuclear weapons. South Africa too succeeded in making fission bomb. The surprise for Occidental countries has been to discovered that India , China and Pakistan also succeeded in making fission bombs. It means that for qualified scientists the making of atomic bombs is not so complicated, it is the reason why IsraŽl is assassinating Iranian scientists, technicians and engineers (Le Canard enchaÓnť- Mercredi 14 Octobre 2009). I wonder to know why that policy is not applied in all the world, since zero nuclear weapon means also zero nuclear scientist.

   Pacific uses of nuclear energy

Nuclear energy is the energy released by the splitting of an uranium nucleus when a neutron comes inside. The uranium nucleus breaks itself in two smaller nuclei; the energy of fission corresponds approximately to the electrostatic Coulomb energy required to unite both smaller nuclei. In other words, it is the repulsion energy of fragments of fission ; it means you may produce a lot more of energy if you are able to disintegrate the uranium nucleus... like Trinitium fluoride.
Fission bomb is the very fast release of fission energy of uranium. A nuclear reactor is the controlled release of fission energy. You may have reactors mainly focused to the production of heat. Technology of nuclear reactors is described in specialized books; you have to know that uranium combustible in gained with zirconium alloy to prevent its mixing with fluid that recuperates the heat.
Research reactors are mainly focused on the production of high neutron flux to produce short lives radioisotopes for medical uses (scintigraphy, tomography), analysis by activation of a sample.



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