VOLUME 20 (5)/October 1990

Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
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institute for Nuclear Research and Nuclear Energetics, Bulgarian Academy of Sciences, 1784 Sofia
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Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
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Institute of Geochemistry and Physics of Minerals, Academy of Sciences of the Ukrainian Soviet Socialist Republic, 25 2068 Kiev, 68