<研究論文>中性子放射化分析法による鉱化および非鉱化の花崗岩中のタングステンの定量

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Tungsten content in granitic rocks is precisely determined by an instrumental neutronactivation analysis method (INAA) using several standard samples. Natural geostandard rocksare GSJ geostandard of JG-l. JG-la, JG-2, JR-2 and JR-3, and artificial standardmaterials of JR-2 with added scheelite powder and tungsten-doped quartz sand were employed forthe analysis. Each sample (lOOmg) was irradiated for short time (l min, 2 min and 3 min) atthermal neutron flux 2.8 X 1013 nlcm' Is and for long time (60min) at thermal neutron flux 2.3 X1013 n I cm2 I s. Gamma-ray spectrum of 187 W at 685.72 keY was used for the tungstenanalysis in geostandards. The 187W gamma-ray spectrum was not recognized for Na-rich JG-l(W concentration = 1.5 ppm), while the gamma spectrum of that was recognized for JR-2 (1.8ppm). SiN ratios of 187W for geostandards that irradiated for 3 min and after cooling for 6 daywere higher than those of another irradiation conditions. The analytical error of tungsten ingeostandards with the confidential limit of 95% was ± 4.7 ppm. This INAA with 3 minirradiation is the most suitable method for the tungsten-bearing samples was successfullyapplied to wide range of tungsten (i.e. low W concentration of non-mineralized granites to high Wconcentration of mineralized granite and scheelite-bearing ore).