Neutron Moisture Meter – Nuclear Physics Helps Farmers
‘Nuclear’ – What comes to your mind when you hear this word? Weapons, Defence, and Medicine... But it has far more applications than these, particularly in Agriculture. One of the most famous applications of Nuclear Physics in the field of Agriculture is the use of radioisotopes. Here we are going to see one such radioisotope that helps in measuring the most important factor for agriculture – soil moisture.
The Neutron Moisture Meter (also known as neutron probe) is one of the most accurate and non-invasive techniques to measure soil moisture. The probe is lowered into the soil via access tubes dug in the soil.
Physics behind it
As the name suggests, Neutron Moisture Meter is an instrument used to measure the water content in the soil. The general scheme of a neutron moisture meter consists of two major components - i) source probe and ii) detector. The probe usually consists of an alpha particle emitting radioactive source (E.g. Americium-241) and Beryllium. When hit by the alpha particle emitted, Beryllium loses one neutron and gets converted to Carbon.
The released high energy neutrons lose energy when they collide with the hydrogen atoms in the soil, they become slow neutrons. The detector is calibrated such that it measures the reflected slow neutrons. But the number of slow neutrons is directly proportional to the number of hydrogen atoms in the soil. Source of hydrogen atoms in the soil is mostly water. By looking at the gauge attached to the detector, we can measure the water content in the soil.
- Access tubes should be installed already at the site.
- Insects and foreign materials should be prevented from accessing the access tube.
- Not sensitive at shallow depths (effective depth - more than 6 inches).
- Skilled personnel required since the instrument consists of a radioactive source.
* Image Courtesy Pixabay.com