3. Neutron scattering method

3. Neutron scattering method
    Fast neutrons are emitted by neutron emitters; viz. radium-beryllium or americium-beryllium. The fast-moving neutrons interact with the hydrogen atoms and get slowed down. The number of slow moving neutrons returned back after colliding with the hydrogen is proportional to the quantity of water present in the soil as water is considered to be the sole source of hydrogen atoms. The slow moving neutrons are detected by proportional or scintillation counters and interpreted in terms of moisture percentage at different depths.
    Advantages
    • Nondestructive
    • Possible to obtain profile of water content in soil
    • Water can be measured in any phase
    • Can be automated for one site to monitor spatial and temporal soil water
    • Measurement directly related to soil water content

    Disadvantages
    • Costly
    • Dependent on dry bulk density and salinity
    • Radiation hazard
    • Must be calibrated for different types of soils
    • Access tubes must be installed and removed
    • Depth resolution questionable
    • Measurement partially dependent on physical and chemical soil properties
    • Depth probe cannot measure soil water near soil surface
    • Subject to electrical drift and failure

Last modified: Thursday, 10 May 2012, 5:09 AM