Determination of oxygen and silicon in rocks by 14-MeV neutron-activation analysis and its precision

Oxygen and silicon have been determined in the six new U.S. Geological Survey standard rocks and two standard refractory materials by 14-MeV neutron-activation analysis, followed by both single and multichannel analyser counting of the induced (16)N (4.5-8 MeV gamma radiation) and (28)Al activities (1.78 MeV photopeak). Owing to the long analysing time per pulse, dead-time corrections are necessary in multichannel analyser counting. Four methods were investigated in this work: counting in the live-time mode without additional correction, short counting corrected by an external live-time scaler, the method of Bartoseck, and the method of Schonfeld. Each measurement was controlled by a simultaneous measurement with a single-channel analyser. Silica ignited at 1000 degrees was used as a reference. Correction was made for the interfering elements, F, P, Al, Fe and Mg, using literature data. Attention was paid to neutron, gamma and beta attenuation. For oxygen the mean coefficient of variation for a single determination with a single-channel analyser was 1.7 % for silicon 1.1 %. The mean results for single-channel counting were compared with literature values.