Nuclear reaction analysis
As Nuclear reaction analysis ( Nuclear Reaction Analysis or nuclear reaction analysis) is called a class of methods in physics and materials science. It serves the investigation of material compositions.
Wherein NRA the sample is bombarded with an ion beam. Typical beam energies move in the range from 100 keV up to several 10 MeV. For material analysis of nuclear reactions are used, caused by the interaction of the particle with the sample atoms.
For analysis, resulting alpha - and gamma radiation used. According to the reaction, the radiation each also has a certain sharply defined energy. Thus it is possible to measure the concentrations of individual isotopes of the surface layer of a sample. The yield of this except the isotope concentration, among other things, depending on the cross section. The used ion beam must therefore be chosen to match the isotope to be detected. In general also true that higher beam energies increase the cross -section and thus for the same beam current lead to a higher signal yield. On the other hand, occur with higher beam energy as well as unwanted side reactions that can interfere with the measurement.
NRA is suitable for the examination of the surface of samples. Analyzable the depth increases with the beam energy and decreases with the ordinal number of the ions. It also depends on the limited framework of the sample composition. In general, it moves in the micron range. As with a certain beam energy and a certain type of ion is usually only one element, or at least a limited number of elements can be detected are necessary to fully characterize the sample usually additional analyzes with other methods.
The method is suitable for its isotopic selectivity especially for the detection of trace elements, but also for the analysis of processes by means of certain tracer isotopes. In addition, it is used primarily for the detection of light elements.
A special case is the resonant NRA (English Resonant Nuclear Reaction Analysis, also known as nuclear resonance reaction analysis referred ) dar. In this method one uses nuclear resonances to the greatly increased cross sections of a reaction in a narrow energy interval lead. Accordingly dominates in the region above the resonance energy of the resonance signal, the yield. Since it takes the sample to a gradual loss of energy of the ion beam, the beam will only in a specific layer of the sample at the resonance energy. To use just the resonance energy is measured in accordance with the surface concentration of the isotope, increasing the beam energy, the beam must initially lose energy before the resonance energy is reached. Deeper and deeper layers of the sample so it can be analyzed. Accordingly, one obtains a low -resolution image of the isotope concentration.