Neutron probe

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  • Neutron Probe
definition
  • A neutron probe is not measuring water content directly. It is measuring hydrogen atoms and these can be from any source, including bound water and hydrocarbons. The use of a neutron probe in environmental, or environmental remediation applications usually requires frequent site recalibration due to changes in the hydrogen provided by sources other than water. In addition, a neutron probe is not accurate within the top 15 cm. of the soil surface due to neutron loss from the region of influence into the atmosphere. The user of a neutron probe usually requires special training, and a government license for transport, ownership and use of a radioactive source. The soil core from the probe borehole must be gravimetrically analyzed to establish a calibration reference curve to insure probe accuracy, and the site calibration curve is specific to a particular probe. Additionally, neutron probes "age" with use as the activity level of the source degrades. This "aging" of the probe requires periodic site recalibration to maintain accuracy. Additional information available at "http://www.esica.com/products/moisture/tech.htm" [Summary provided by ESI]
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Abstract from DBPedia
    A neutron probe is a device used to measure the quantity of water present in soil. A typical neutron probe contains a pellet of americium-241 and beryllium. The alpha particles emitted by the decay of the americium collide with the light beryllium nuclei, producing fast neutrons. When these fast neutrons collide with hydrogen 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.

    (Source: http://dbpedia.org/resource/Neutron_probe)