High Precision Determination of Silicon in Rocks by Fast-Neutron Activation Analysis

Silicon is determined by irradiating powdered rock samples with 14-MeV neutrons in a system that allows dual transfer of samples. The 1.78-MeV gammas of the ²⁸Al produced are counted as representing silicon in the sample. The unknown and reference sample positions for irradiation and counting are switched on consecutive irradiation count cycles with four of these cycles constituting a single determination. The standard deviation for a single determination is 0.12% silicon. Pure quartz is used as a reference. Results of analysis of some standard rock powders compare favorably with accepted values. New values are given for 10 standard rocks.