A neutron probe is a device used to measure the quantity of

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

present in

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...

. A typical neutron probe contains a pellet of

americium-241 Americium-241 (, Am-241) is an isotope of americium. Like all isotopes of americium, it is radioactive, with a half-life of . is the most common isotope of americium as well as the most prevalent isotope of americium in nuclear waste. It is c ...

and

beryllium Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form m ...

. The

alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be pro ...

s emitted by the decay of the americium collide with the light beryllium nuclei, producing fast neutrons. When these fast neutrons collide with

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

nuclei present in the soil being studied, they lose much of their energy. The detection of slow neutrons returning to the probe allows an estimate of the amount of hydrogen present. Since water contains two atoms of hydrogen per molecule, this therefore gives a measure of soil moisture.

References

* : Google Translate: "Establishment of soil moisture measurement points, calibration of a neutron probe at the instance of the type Wallingfordsonde iH11" Probe Soil physics {{nuclear-stub

See also

References