A particular application of NIS is where a probe containing a neutron source can be lowered into a bore hole where the radiation is scattered by collisions with surrounding soil.
Since hydrogen (the major component of water) is by far the best scattering atom, the number of neutrons returning to a detector in the probe is a function of the density of the water in the soil.
Just as X-rays show a break in a bone, gamma rays show flaws in metal castings or welded joints.
The technique allows critical components to be inspected for internal defects without damage.
Gamma radiography works in much the same way as X-rays screen luggage at airports.
Instead of the bulky machine needed to produce X-rays, all that is needed to produce effective gamma rays is a small pellet of radioactive material in a sealed titanium capsule.
To measure soil density and water content, a portable device with an americium-241-beryllium combination generates gamma rays and neutrons which pass through a sample of soil to a detector.
(The neutrons arise from alpha particles interacting with Be-9.) A more sophisticated application of this is in borehole logging.
Nuclear techniques are increasingly used in science, industry and environmental management.
The continuous analysis and rapid response of nuclear techniques, many involving radioisotopes, mean that reliable flow and analytic data can be constantly available.
The energies of the fluorescent X-rays emitted can identify the elements present in the material, and their intensity can indicate the quantity of each element present.
This technique is used to determine element concentrations in process streams of mineral concentrators.
Elements detected this way include iron, nickel, copper, zinc, tin and lead.