Nuclear reaction analysis

As a nuclear reaction analysis ( N uclear R eAction A nalysis or nuclear reaction analysis ) is in a class of methods physics and materials science refers. It is used to investigate material compositions.

Procedure

In NRA, the sample is bombarded with an ion beam with an energy usually in the range from 100 keV to several tens of MeV. For material analysis, nuclear reactions are used that arise through the interaction of the particle beam with the sample atoms and emit alpha and / or gamma radiation . Depending on the reaction, the radiation has a specific, sharply defined energy. The concentrations of individual isotopes of the surface layer of a sample can be measured if the ion beam has been selected to match the isotope to be detected.

The radiation yield depends not only on the isotope concentration but also on the cross-section . In general, higher beam energies increase the effective cross-section and thus the signal yield with the same beam current. On the other hand, undesirable side reactions occur with higher beam energy, which can have a disruptive effect on the measurement.

NRA is suitable for examining the surface of samples. The depth that can be analyzed increases with the beam energy and decreases with the atomic number of the ions. It also depends somewhat on the sample composition. Usually it is a few micrometers.

Since only one or a few elements can usually be measured with a certain beam energy and ion type, additional analyzes with other methods are usually necessary in order to fully characterize the sample.

Due to its isotope selectivity, the method is particularly suitable for the detection of trace elements, but also for the analysis of processes using certain tracer isotopes. It is mainly used for the detection of light elements.

Resonant NRA

A special case is the resonant NRA (Engl. R esonant N uclear R eAction analysis, short RNR Analysis) is also known as nuclear resonance reaction analysis referred. This method uses nuclear resonances , which lead to greatly increased cross-sections of a reaction in a narrow energy interval. Accordingly, in the area above the resonance energy, the resonance dominates the signal yield.

Since the ion beam gradually loses energy in the sample, the beam only takes on the resonance energy in a specific layer of the sample. If the resonance energy is used, the surface concentration of the isotope is measured accordingly. If the beam energy is increased, the beam must first lose energy before the resonance energy is reached. So ever deeper layers of the sample are analyzed. Correspondingly, a depth-resolved image of the isotope concentration is obtained.

See also

• Surface chemistry

Web links

• Principle of Nuclear Reaction Analysis (NRA) (PDF file; 5.02 MB)
• Investigations into the high-rate deposition of hard DLC layers (PDF file; 2.86 MB)

Individual evidence

1. ↑ JC Alonso: Fluorine content of SiOF films as determined by IR spectroscopy and resonant nuclear reaction analysis . In: Journal of Vacuum Science & Technology A . tape 25 , 2007, p. 448-454 . ( Publication text ( Memento of the original from March 21, 2016 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this note. )