Silicon and aluminium determination in geological samples by 14 MeV neutron activation based on simple equipment

An internal comparator method was developed to determine silicon and aluminium contents in geological samples by 14 MeV neutron activation. This method is particularly suitable for modestly equipped developing neutron generator laboratories. In the present work vanadium was chosen as the comparator element mixed into the powdered samples. The reproducibility of this method was good despite the cylindrical tubes of pneumatic transfer system in which the sample positioning at the irradiations and detection positions is random. The standard samples were prepared from pure chemical compounds. Using this method international rock standards were analysed. The results obtained agreed within 2% with those obtained by other methods. The detection limits for the present method have been determined under realistic background conditions. These are 2.4 mg for Al and 0.3 mg for Si at a neutron flux of 108 cm-2s-1 for 5 min irradiation time, 5 min measuring time using a 20 cm3 Ge/Li/detector and allowing +-10% statistical error. These limits of detection are higher than the published values based on theoretical calculations only. A catalogue of 14 MeV neutron produced gamma spectra of possible comparator elements would be useful to extend the internal comparator method for determination of other elements. (author)