Neutron Measurement of Soil Moisture in China

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The application of neutron measuring water in foreign countries began in the 1950s.
China Neutron Instrument was developed in the 1960s. During this period, its application was mainly applied to automation equipment. In the 1970s, the neutron meter developed by Nanjing University and Lanzhou University was put into use, and the raw material moisture and raw material thickness were continuously measured in industrial automation. The specific surface area of ​​the material, the hydrogen content of the measured material, etc. have been widely used; the method of measuring the volumetric moisture content of the soil by the neutron meter is a branch of the water measurement application. At present, the measurement accuracy and accuracy of the neutron meter produced can fully meet the demand for soil water measurement. However, the design application environment is inconsistent with the actual application environmental conditions. This is not completely consistent, resulting in a certain error in the measurement. Neutron determination of soil moisture calibration curves can be used to more accurately determine soil moisture.
At present, the methods for measuring soil moisture include: drying method, neutron meter method, gamma ray method, soil moisture meter method, time domain reflectometry, and frequency domain reflectometry. The determination of soil moisture by the neutron meter is one of the main methods in soil moisture determination, and it is also an easy-to-use method for determining soil moisture. The types of neutrons for measuring soil moisture mainly include embedded type, surface type, transmission type, and scattering type. The neutron measurement instrument that measures the water content of soil in situ is generally an embedded type neutron measurement instrument. The embedded neutron instrument water meter works by embedding the neutron source into the soil to be measured. The neutron source continuously and rapidly emits fast neutrons, and the fast neutrons enter the soil medium and collide with the nuclear atoms of various atomic ions. Neutrons lose energy and slow it down. The moisture content in the soil is determined by determining the functional relationship between the density of the slow neutron cloud and the water molecules.
The measurement of soil moisture based on the neutron meter is an important method. The error of water measurement by the neutron meter is mainly caused by the actual measurement of the environment. This phenomenon is widely used in water measurement by neutron meter, and the application of soil water measurement and industrial automatic water measurement is summarized. The progress made, with reference to the principle of water measurement, the measurement of soil water by the neutron meter, proposed feasible methods for improving the calibration curve of soil moisture measured by a neutron meter.
High-precision neutron moisture meters have been developed to meet the needs of soil moisture accuracy. Research on improving the accuracy of neutron moisture meters in measuring soil moisture content has a certain depth and breadth, and can be in different textures, different bulk density, different seasons and different Soil volume moisture content is stable and reliable application. Among them, the determination of the stratified distribution of soil volumetric moisture needs to be further improved. The main neutron measurement instrument is assumed to be linear in the infinite (relatively fast neutron diffusion distance) uniform medium, the neutron count and the soil volumetric moisture content can be linear, and the layered soil moisture profile variation is not strictly in line with the requirements of the instrument measurement. Therefore, the research in this area needs further in-depth study.
Under the condition of varying levels of soil moisture content, in-depth study on the influence of water content in different soil layers on the neutron count should be based on the study of 3-point smoothness and volumetric smoothness of soil moisture, revealing that different levels of water content have neutron counts. The degree of influence.

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