Gamma ray attenuation for determining soil density: laboratory experiments for Environmental Physics and Engineering courses

Abstract In this paper, we present in details a method for determining the soil density of disturbed samples. The mass attenuation coefficient was also evaluated by using the relation between the number of photon counts and the path length (soil density \texttimes thickness). A typical student laboratory setup (PASCO) was utilized in the measurements. A gamma ray source of 137 Cs and soils with four different textural classes were employed. The experimental apparatus here proposed, that uses an educational gamma ray attenuation system, permitted measuring, with very good agreement with the traditional method, the density of soil samples. The experiment can be somehow extended by proposing the investigation of soil bulk variations due, for instance, to soil compaction, a subject of interest for engineering and environmental physics students.

摘要 本文详细阐述了一种扰动土样土壤密度的测定方法。本研究借助光子计数与光程长度（土壤密度×厚度）之间的关系，对质量衰减系数进行了估算。实验采用经典的学生实验室装置（PASCO），以铯-137（¹³⁷Cs）作为γ射线源，并选用四种不同质地类别的土壤样本开展测试。本研究提出的这套搭载教学用γ射线衰减系统的实验装置，其测得的土壤密度与传统方法结果吻合度极佳。该实验可进一步拓展，例如可开展土壤压实导致的土壤容重变化相关研究，这一主题也是工程与环境物理专业学生的关注热点。