[en] Substances existing in the starting material for production of silicon crystals are responsible for part of the impurities in the resultant silicon crystals while the remaining of the impurities are accounted for by substances entering the material during the production of semiconductor devices. It is of great importance to make an analysis of impurities contained in the original crystal material. Such crystal material is so high in purity that a quantitative analysis technique to be used should be able to determine ppt-level impurities. The present report outlines the mechanism of an neutron activation analysis method which can be applied to the determination of impurities in crystal material. When a sample for analysis is fed into a nuclear reactor, neutrons resulting from the fission of ²³⁵U hit nuclei to cause nuclear reactions, to convert the nuclei into different forms of nuclei. Such product nuclei are generally radioactive and disintegrate into daughter nuclei while releasing beta- and gamma-rays. The types and amount of elements contained in the original sample can be identified and determined by analyzing the energy of the released gamma-rays. (N.K.)