Determination of soil density and water content by fast neutrons and gamma rays

Sequential measurements of gamma and fast neutron attenuation were used for nondestructive determination of both soil density and water content of soil samples. Soils containing known amounts of water were packed into 22.5-cm diameter cylinders to a depth of ∼9 cm. Measurements were made of attenuation of fast neutrons from a 3-μg 252Cf source and attenuation of gamma rays in a collimated beam from a 137Cs source. The attenuation was used to calculate the soil density and water content of these samples. The mean difference between the calculated and known water contents was 0.006 g/cm3 with a standard deviation of 0.010 g/cm3; the mean difference for soil density was 0.010 g/cm3 with a standard deviation of 0.017 g/cm3. Calculations based only on counting statistics show that an attenuation method using a combination of gamma and fast neutrons is better than a method using two gamma energies.