Abstract
Silicon carbide and nitride have been attracting a special attention as heat-resisting materials in relation with the energy problem. The oxygen in these materials is considered to be related with their thermal-shock-resisting ability. If ordinary methods are employed for the analysis of the oxygen in such materials that contain silicon as a matrix element or as a major constituent, there arise many difficult problems yet to be solved. It is expected, however, that these material can be analyzed rather rapidly, non-destructively and accurately by the 14 MeV neutron activation analysis if a proper consideration is given to the random sum of γ-rays from 28Al produced by the 28Si (n, p) reaction. This becomes appreciable when a large amount of the sample and/or high 14 MeV neutron flux are used in order to increase the sensitivity. The relation between the saturation activity, A∞ (nf σ), and the random sum counting rate was studied. The random sum of the 28Al γ-rays themselves must be taken into consideration when the A∞ value is high. The apparent half life of the random sum counts was calculated as 69.3 s, and accurate decay analyses of γ-rays were obtained by using this half life as the additional factor. The A∞ value must be kept less than 1.2 × 105 s-1 so as to avoid the fatal interference caused by the triple random sum of 28Al. The external standard method was adopted. By the present method, oxygen contents were determined to be (0.061.40) % for 20 kinds of silicon samples, 20.0 % for a carbide sample and (0.943.05) % for 13 kinds of nitride samples.
