INDUSTRIAL APPLICATIONS AT RADIATION SOURCES

I.L. Komov

National Academy of Sciences, 34, Palladin av., Kyiv-142, Ukraine, 252680, E-mail: gnc-r@mail.kar.net

The use of the method of radiation mineralogy in the analysis of crystallographic phenomena indicates their great potential in the solving of scientific and practical problems. The internal structure of natural crystals is distinctly revealed by gamma-irradiation, disclosing the history of the growth and development of individual grains. As it follows from the patterns that are produced, an inhomogeneous internal structure is established in natural crystals. The modifications in the internal structure (zonality, sectorial and mosaic structure, traces of dissolution-regeneration) correlate with the content of structural impurities and their mode of occurrence. This patterns of originally homogeneous and transparent minerals as revealed by gamma-irradiation are the reflections of these properties. Irradiation and etching supplement each other and allow the visualization of different elements of the real structure of crystals, and can decipher changes in physico-chemical parameters during growth of crystals. With a gradual change of the colour, the crystals are characterised by high quality. A study of mineral zonality allows one to judge the conditions of change in the state of mineral systems. Dissolution and regeneration zones are established in absolutely homogeneous transparent minerals after irradiation. The incoherence creates stresses producting fissures round them, and evokes considerable changes in the composition and lattice parameters, which become visible after irradiation, but cannot be defined by chemical analyses. Minerals subjected to irradiation preserve a "memory" of changes due to the ionization processes. "Memory" acquired during mineral irradiation depends on the absorbed dose and type of radiation.

The method of gamma-irradiation, which permits fixation of the radiation colour character, helps to determine the simultaneity of spatially separated formation and thus to judge the relative synchronism of crystals. They are discussed as well-known so and new methodically approach, which are helped to ennobling minerals. Considerable amounts of the off-grade material with faded colours and pale patterns occur together with high-standard semi-precious crystals. This decreases the gem and decorative qualities of minerals and sometimes precludes their use for such purposes. The colour, contrast range of pattern, and brightness of different minerals can be changed by gamma-irradiation combined with physical and chemical treatment of the original samples.

A number of methods to change or intensify the colour have been developed. Gamma-irradiation turns colourless transparent beryl into light green and high radiation doses give them a saturated blue-green colour, resulting in rather attractive stones. If the beryl is originally yellow or green, it acquires a blue-green or green colour. Centres of dark-blue colour can appear in some beryl crystals irradiated by both gamma-quanta and neutrons. The highest variability of colour is found in aquamarine, which colour can be fixed or intensified by gamma-irradiation and annealing. To ennoble beryl it is expedient to use hydrothermal treatment of samples in autoclaves, where green beryl, when heated, becomes bright blue. Topaz constitutes valuable material for cutting, but usually about 30% of crystals (by mass) are colourless or weakly coloured. Large amounts of non-standard material, which is unwanted, accumulate at the deposits. Depending on the kind and conditions of irradiation, topaz can be coloured braun or blue. But after gamma-irradiation, the colour is unstable and weakens as it becomes affected by sunlight. The reactor-induced irradiation, when the mineral becomes blue or dark blue, is the most efficient method of ennobling topaz. The effect of long-term exposure of the specimens to daylight after irradiation is a disadvantage of the method. A combination of the methods of technological modification of colour permits increasing of the yield of high standard raw materials for the jewellery industry. The ennobling of natural gemstone raw materials improves below-standard material to the production standards. The use of a combination of methods is particularly efficient. They are: physical (irradiation) with thermal treatment in furnaces or autoclaves in combination with colouring by chemical reactions within the material and surface coloration by organic dyes. In addition to its technological value, ennobling makes possible a more profound study of the typomorphic properties of minerals to find the features characteristic of natural varieties of coloured stones and their imitations. This is especially important for different natural and synthetic minerals in which charateristic defects and zonality are found by gamma-irradiation and physical methods of investigation. The number of minerals used in industry can be increased by the applications of irradiation. Locality, sensitivity, amount of information, and documentality are the important features of this method.