Nuclear Reaction Analysis (NRA)

Nuclear Reaction Analysis (NRA)

Nuclear reaction analysis (NRA) is an analytical method used for quantifying and depth profiling of some light elements and isotopes in the surface and near surface regions of solid materials. In the NRA technique, an ion beam using light projectile nuclei of known mass and energy, impinges upon nuclei of the target element at incident energy levels exceeding the coulomb barrier of the target. This results in nuclear reactions between the incident ions and the target nuclei, yielding light and heavy nuclear reaction products with different energy levels, emitted at different angles. The energy level of the reaction products depends upon the incident ion mass and energy, the target atomic mass, product emission angles, masses of light and heavy reaction products and the energy released in the nuclear reaction. The emitted particles are detected by solid state detectors and energy spectra are produced, from which the target elements in the sample can be quantified. The incident ions used in NRA are protons (¹H), deuterons (²H), ³He or alpha particles (⁴He). Interference from backscattered particles can be eliminated using absorber foils to filter out the interference, based on the relatively higher energy of nuclear reaction products.

Due to the isotope-specific nature of nuclear reactions, NRA can be used for isotope identification and mapping. However, for a given incident ion species and energy, only one (or a few) isotopes can be detected, so several repetitions would be needed with varying energy levels or incident ion species for complete analysis. Depth profiling to obtain concentration variation of a specific isotope can be done by non-resonant NRA or resonant NRA, depending upon the reaction cross section of the sample.

Common Uses of Nuclear Reaction Analysis (NRA)

• Trace impurity analysis in thin films
• studying the surface and subsurface reactions of hydrogen in metals.
• Depth profiling of light elements in thin films
• Isotope tracing in surface and near surface regions of solids

Advantages of Nuclear Reaction Analysis (NRA)

• Due to its isotope selectivity, the method is particularly suitable for the detection of trace elements, using certain tracer isotopes.
• Non-destructive testing technique
• Sensitive to Trace concentrations  
• Depth resolution from a few nanometres to a few microns. 

Limitations of Nuclear Reaction Analysis (NRA)

• More than one reaction is possible on some nuclei, yielding different product characteristics and spectra, causing difficulty in interpretation.
• Reference targets containing known amounts of the detected element are sometimes needed, due to the uncertainty or unavailability of nuclear cross section data.
•  Protons created in nuclear reactions may have excessive energy that overcome detection capacity of conventional detectors.be very high.

Industrial Applications of Nuclear Reaction Analysis (NRA)

• Semiconductor research and quality control
• Metallurgy research and quality control
• Polymeric thin films and coatings quality control