Effects of inhomogeneity and contamination in k0-INAA of low (K, Th, U)-content sand for the annual radiation dose determination in luminescence dating

It was demonstrated that for the determination of the annual radiation dose for use in luminescence dating of sediments, one should be aware of possible material inhomogeneities when applying analysis methods (such as k0-INAA) with sample intakes of the order of the gram (to be compared with Ge gamma-ray spectrometry in cylindrical or Marinelli geometry, the latter involving ∼1.5 kg material). Moreover, when trying to remove the inhomogeneity, care should be taken to avoid contamination of the elements investigated, especially in the case of low (K, Th, U)-content sand with a considerable abrasive action (such as the Ossendrecht coversand dealt with in the present work). Whereas contamination was indeed shown to happen when grinding the material in a porcelain mortar, a satisfactory technique proved to be agate-ball milling.