リリーフ消去法による屈折率測定の精度

抄録

The relief of a mineral fragment under a polarizing microscope depends on the refractive index difference between the mineral and a surrounding medium, |Δn|. The relief with a certain value of an can be eliminated by increasing the angular aperture of the substage condenser over a critical value, 2θ. Refractive indices of the mineral fragments immersed in a medium of known refractive index can be estimated from the relation between |Δn| and 2θ. The method was tentatively called “Relief extinction method” by Takubo (1988). The accuracy of refractive index estimation by this method was examined by a statistical method. A conventional objective lens and three types of condensers were used in the experiment. Several relationships were empirically found among 4n, guide numbers of the iris diaphragm of condenser, F, and virtual values of 2θ. The deviation of refractive index, δ, was estimated from these relationships and the standard deviation of F, σ. The accuracy of refractive index measurement decreases with increasing |Δn|, F and 2θ values. A com-bination of the relief extinction and the Becke line method will promote the efficiency in the refrac-tive index measurement.