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The gemstone irradiation is a process in which a gemstone is artificially irradiated in order to enhance its optical properties. High levels of ionizing radiation can change the atomic structure of the gemstone's crystal lattice, which in turn alters the optical properties within it. As a result, the gemstone's color may be significantly altered or the visibility of its inclusions may be lessened. The process, widely practised in jewelry industry, is done in either a nuclear reactor for neutron bombardment, a particle accelerator for electron bombardment, or a gamma ray facility using the radioactive isotope cobalt-60.〔〔 ''This article incorporates text from the source, which is in the public domain.''〕 The irradiation enabled creation of certain gemstone colors that do not exist or are extremely rare in nature.〔 ==Radioactivity and regulations== The term ''irradiation'' is a very broad one, which covers bombardment by subatomic particles as well as the use of the full range of electromagnetic radiation, including (in order of increasing frequency and decreasing wavelength) infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. Certain natural gemstone colors, such as blue-to-green colors in diamonds, are the results of the exposure to natural radiation in the earth, which is usually alpha or beta particle. The limited penetrating ability of these particles result in partial coloring of the diamond's surface.〔 Only high-energy radiation such as gamma ray or neutron can produce fully saturated body colors,〔 and the sources of these types of radiation are rare in nature, which necessitates the artificial treatment in jewelry industry. Irradiation, particularly when done in a nuclear reactor, can make gemstones slightly radioactive, so they are typically set aside for a couple of months to allow any residual radioactivity to decay.〔 The first documented artificially irradiated gemstone was created by English chemist Sir William Crookes in 1905, by burying a diamond in powdered radium bromide. After having been kept there for 16 months, the previously colorless diamond became green.〔 This method produced a dangerously high degree of long-term residual radioactivity and is no longer in use. However, radium-treated green diamonds are still occasionally found in markets, which can be detected by a Geiger counter or by making autoradiographs on photographic films.〔 The concerns for possible health risks related to the residual radioactivity of the gemstones led to government regulations in many countries.〔 In the United States, the Nuclear Regulatory Commission (NRC) has set strict limits on the allowable levels of residual radioactivity before an irradiated gemstone can be distributed in the country.〔 All neutron- or electron beam-irradiated gemstones must be tested by an NRC-licensee prior to release for sales.〔 In India, the Bhabha Atomic Research Centre started irradiating gemstones in the early 1970s. In Thailand, the Office of Atoms for Peace (OAP) conducts the process for private sectors, irradiating of gemstones from 1993 to 2003. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Gemstone irradiation」の詳細全文を読む スポンサード リンク
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