Student Corner: Measuring Moisture Content of Soil

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By Abram Teplitskiy

After receiving a degree in physics, the author got a job in the construction industry at a scientific research institute and started to be involved in developing nuclear gauges for measuring physical-technical properties of soil, concrete and other construction materials. Nuclear density devices are based on using source of gamma radiation for operation.

Another type of radiation – neutrons – are used for measuring the moisture content of soil. The mass of a neutron is practically equal to the mass of an atom of hydrogen. Because of this closeness, it is possible to use a neutron gauge to determine the moisture content of soil. By inserting a gauge with a neutron source in soil, the neutrons will interact with the nucleus of the hydrogen atoms, and as a result they will lose some energy. "Quick" neutrons become "slow" neutrons after such interactions. The figure below shows possible dispositions of sources and sensors of nuclear radiation for measuring soil's moisture content.

Sources and Sensors for Measuring Soil's Moisture Content 1 – source of neutron radiation; 2 borings; 3 holders; 4 cables;   5 – borings; 6 – soil; 7 – radiation counter; 8 – scattered neutron radiation counter; 9 – directional plate

The measuring technology includes the following options:

• Measuring density and/or moisture content of soil through vertical or inclining boring – using a gamma device for testing the density of the soil or a neutron device for measuring the moisture content of the surrounding soil
• Measuring the density of soil by scattering gamma-quanta in one vertical boring
• Measuring the density or moisture content of soil by scattering gamma quanta in surface layers of soil strata
• Measuring vertical or three-dimensional movements of radioactive sensors inside soil strata
• T-like scheme of measurements of density of moisture content by attenuation or/and scattering of gamma radiation or/and neutrons

Nuclear methods (neutron and gamma) are direct methods of determining the density and moisture content of soils (and other materials).

In the Theory of Inventive Problem Solving (TRIZ) It is important to understand the science "effects" in order to use the resources of a system. In this case, the water content of the soil is a resource, and is also a good material for slowing the neutrons. The inventor of this device would need to know the science, know how to search for "things that slow down neutrons" or "things that interact with radiation."

Happy inventing!

About the Author:

Abram Teplitskiy, Ph.D., is a consultant for inventing, applied physics and civil engineering. Contact Abram Teplitskiy at tepl (at) sbcglobal.net.