Neutron Investigation of the Rate of Water Seepage from Irrigation Channels and Reservoirs on Loessial Loams

The author discusses the results of experimental field studies on moisture conditions in the ground near an irrigation channel and a reservoir and the area of ground affected that were carried out in 1968 with neutron moisture gauges and gamma-gamma densimeters. Observations of the moisture movement and soil density were made in permanent boreholes up to 16.5 m deep lined with 2-in. steel tubes sealed at the bottom. To measure the moisture use was made of an all-purpose probe with a high-efficiency slow-neutron detector of the LDNM type (ZnS(Ag) + B2O3), which was contained in the probe alongside a Pu + Be neutron source, thereby making it possible to obtain a linear dependence between the thermal neutron count and soil moisture. A portable scaler was used as the measuring instrument. When recording soil density, the LDNM scintillation crystal in the probe was replaced by a Nal(Tl) single crystal and a lengthener with a steel screen was screwed onto the probe casing. The conical end of the lengthener contained a gamma source (137Cs) with an activity of 2 meq of radium. In this case the length of the probe was-35 cm. On the basis of these studies the author determines the rate at which the soil near the reservoir is moistened and establishes the areas of loessial loams moistened by the irrigation channel. (author)