NRA (Nuclear Reaction Analysis)
Under the right conditions, accelerated particles interact with the target atom nucleus, giving off gamma rays or secondary particles.
The light elements, from hydrogen to fluorine, are not easily analyzed by conventional RBS or PIXE techniques. In many cases, these elements can be detected by using a resonance effect. Under the right conditions, accelerated particles interact with the target atom nucleus, giving off gamma rays or secondary particles. Certain of these interactions happen only if the incoming particle has exactly the right velocity, that is, the right energy. This resonant effect is put to advantage in NRA.
In a typical case, the mass 15 isotope of nitrogen will interact with hydrogen in the target if the nitrogen has an energy of motion equal to 6.385 MeV. If the nitrogen beam of particles has precisely this energy, and if it hits atoms of hydrogen on the surface of the sample, then gamma ray emission will occur. The gamma rays are measured and used to show the absolute concentration of H on the surface. If the hydrogen is below the sample surface, then the nitrogen will not generate gamma rays unless the beam energy is increased to compensate for the slowing down of nitrogen by the sample. The depth of the hydrogen can therefore be determined by measuring the difference between 6.385 and the beam energy (before it starts through the sample).
Standard NRA techniques currently used in this laboratory allow for measurement of hydrogen, lithium, fluorine, sodium and aluminum. Less often used are measurements for deuterium, boron, carbon, nitrogen-14, oxygen and phosphorus.