Calculation methods for density measurement of soil cores by gamma ray attenuation

Content Partner: Manaaki Whenua – Landcare Research. The technique for measuring density of undisturbed 153-mm soil samples by gamma ray attenuation was applied to measure density of undisturbed 75-mm samples. Some recent improvements to the procedures are described. Previously, the assumed form of relationship (calibration curve) between gamma ray attenuation and sample density caused difficulties with application of the technique to materials with very high water contents. A new form of calibration curve removes this limitation, and the technique has been applied to peat samples with mean water contents exceeding 1000%. Methods for calculating, from an existing calibration curve, the form of calibration curve for differing experimental conditions (e.g., a different sample diameter) are shown, and the relationship between calibration curves for 153-mm and 75-mm samples is discussed.