APPLICATION OF THE GAMMA NEUTRON METHOD FOR TRANSPORT STUDIES IN FIELD SOILS

In order to study water movement in the field, deuterated water was monitored by the.gamma neutron method, using 208Tl gamma source and 3He thermal neutron detector. A laboratory device is presented which supplies measurement data on a 5‐ml soil solution. The performance of a gamma neutron probe is evaluated, the background count rate which depends on soil moisture content is related to the neutron emission of 208Tl gamma source, the resolution is found to depend on gamma diffusion and is no more than 15 cm in unsaturated soil, and the calibration is given versus volumetric deuterated water content. The dispersive transport of a D2O pulse on a soil column is studied through a D2O concentration profile and breakthrough curve at the bottom of the column. Then simultaneous measurements of soil water content and D2O concentration by the neutron moisture gauge and the gamma neutron probe enable us to interpret the evolution of the D2O pulses as a function of irrigation during a field experiment. Copyright 1979 by the American Geophysical Union.