1896 – Discovery of radioactivity
     Radioactivity – the spontaneous emission of radiation by an element – was discovered in 1896 by the French scientist Antoine Henri Becquerel, who observed, from an experiment, that uranium salts emit invisible radiation that passes through paper, wood, glass etc. and then blacken photographic paper. Since then until today, remarkable progress in this area were made, resulting in important benefits of using radioactivity for social and economic development, first of all in power generation, then in dating of rocks to decipher the geological past, in medicine, biology, agriculture, industry and so on, but also giving rise to a global scale concern on the devastating consequences of military use and operational accidents of nuclear power plants, or by using nuclear energy in other areas.
     1898 – Discovery of the first radioactive elements

     Soon after Becquerel’s discovery, two French chemists, Marie and Pierre Curie, have the merit of separating, for the first time, the determining components of uranium ore radioactivity, Marie Curie being the one who coined the term “radioactivity”. Studying together to obtain pure uranium from the uranium ore, the Curies discovered two new radioactive elements: polonium and radium. It will take 4 years and 4 tons of processed uranium ore, to isolate a sufficient quantity of each element, in order to determine its chemical properties. On December 10, 1903, the Stockholm Academy of Science announces the award of Nobel Prize in Physics, half to Henri Becquerel and half to Curies, for discoveries related to radioactivity.

     1919 – First artificial transformation of atoms

    Lord Ernest Rutherford, founder of the planetary structure of the atom theories, discovered the equation of exponential decay process of radioactive elements. Intensively bombarding the nitrogen nucleus with alpha radiation, he obtained oxygen, thus demonstrating the artificial transformation of nuclei and atoms structure.

     1934 – Artificial radioactivity

     Until 1934, only natural radioactive elements are known, but, in 1934, Irene and Frederic Joliot showed that aluminum and magnesium can become radioactive, if they are bombarded with alpha particles from polonium. After the discovery of the radioactivity artificially induced, the problem of using a more energetic source of alpha particles arise, taking into account the potential barrier of the nuclei. And such, the accelerators were built.
    Nowadays, the artificial radioactivity, in fact the radioactive isotopes, are produced by bombardment with charged particles, achieved by using accelerators at convenient energies, or with neutrons, most often in nuclear reactor. This one, the nuclear reactor, is the main source of radioactive isotopes. In both cases, the radioactive isotope is produced by a nuclear reaction.
     Artificial radiation is used in many branches of human activity. For example, in industry is used to control the processes and the products quality; as a purpose of study, is used in research institutes and universities.

       1942 – First nuclear reactor

   The Italian scientist and Nobel Prize winner in 1938, Enrico Fermi, demonstrated that in all elements bombarded with neutrons, transformations of nucleus are occurring. By discovering the slowing down process of neutrons, he made possible the discovery of nuclear fission (by Hahn and Strassmann), leading to the possibility of issuing secondary neutrons and the chain reaction.
     Enrico Fermi and Leo Szillard, were the first ones to build a nuclear pile and they have presented a controlled chain reaction, on December 2, 1942. In 1955, they shared the patent of invention for nuclear reactor U.S. Patent 2,708.656.
     The first U.S. nuclear reactor was used to produce plutonium for nuclear weapons. Other reactors have been used in naval propulsion (submarines and warships).

       1946 – Establishment of United Nations Atomic Energy Commission

     The United Nations Atomic Energy Commission (UNAEC), is the first disarmament negotiating body, created by the General Assembly of the United Nations Organization, on January 24, 1946.

       1956 – Beginning of nuclear energy commercial use
     On December 20, 1951, the electricity was first time generated by using nuclear fission, at Experimental Fast Reactor EBR-1, located near Arco, Idaho.
    In October 1956, at Calder Hall, England, the first nuclear power plant commercially operated is put into operation, while in U.S.A., the commercial use of nuclear energy begins with the prototype reactor PWR Yankee Rowe, driven by Westinghouse, in 1960 and the reactor BWR Dresden-1, designed by General Electric and fully operational in 1960.
     The 1973 Oil Embargo gave a strong impetus to nuclear power generation.
     The most spectacular nuclear program was the French one, which totaled 34,900 MWe.
    Besides U.S.A. (with 20% of electricity generated by nuclear power plants), significant nuclear programs were launched also in many European countries (Germany, Sweden, Spain, Belgium, Italy, Switzerland, Finland, Czech Republic) as in Asian ones as well (Japan, South Korea).
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