Nuclear reaction analysis, element profile

Nuclear reaction analysis (NRA). Based on the detection of charged particles emitted during nuclear reaction, NRA can be considered as an inelastic counterpart of RBS. NRA is useful in the reverse case as for RBS, namely the depth profiling light elements in a sample composed of heavy elements, (e.g. corroded layers on metallic samples containing O, C, and N). Incident ions are protons ( H) or deuterons (2H). 

Nuclear reaction analysis (NRA) and elastic recoil detection (ERD) are part of the suit of ion beam analysis (IBA) techniques. They are commonly used for the elemental depth profiling of materials in a wide range of fields, e.g., from biological and medical to the semiconductor industry. 

The most commonly used accelerator-based techniques for depth profiling are Rutherford Backscattering (RBS) which will be discussed in Chap. 2, Elastic Recoil Detection (ERD) which will be discussed in Chap. 3, and Nuclear Reaction Analysis (NRA) which will be discussed in Chap. 7. PIXE analysis has the advantage of a very good sensitivity and possible simultaneous detection of all heavier elements. 

Nuclear reaction analysis has mostly been applied to problems in material science, where the use of isotopically enriched compounds allows the profile of a specific element to be targeted by ion beam reactions with its isotopes. For example, in the thermal oxidation of silicon, the growth kinetics and diffusion of oxygen across the Si/Si02 interface region has been studied using sequential oxidations in natural and 0 enriched oxygen gas. The differentiation between possible pathways is due to the isotopic specificity of the NRA technique. 

Nondestructive depth profiling, which includes angle-resolved measurements, Rutherford backscattering spectroscopy (RBS), nuclear reaction analysis (NRA), peak intensity measurements from two or more peaks from the same element, and elemental intensity measurements as a function of incident electron energy (3)... 

Megaelectron volt (MeV) ion beam techniques offer a number of non-destructive analysis methods that allow to measure depth profiles of elemental concentrations in material surfaces. Elements are identified by elastic scattering, by specific nuclear reaction products or by emission of characteristic X-rays. With nuclear microprobes raster images of the material composition at the surface can be obtained. Particle-induced gamma-ray emission (PIGE) is especially suited for fluorine detection down to the ppm concentration level. 

NDP is a prompt nuclear analysis technique, which employs a nuclear reaction that results in emission of charged particles with a specific kinetic energy. It is one of the most powerful non-destructive techniques for depth profiling of some light elements especially for and Li, which have very high thermal neutron capture cross-sections of 3837 and 940 barn respectively. 

A wide range of other nuclear reactions have been used in material science for the depth-profiling analysis of a number of different elements, some of which are tabulated by Feldman and Mayer (1986). Whether these techniques will in the future prove useful for polymers remains to be seen. 

In the analysis of light elements by PIGE, the reactions by Coulomb excitation (p, p y) are common. The resonance nuclear reactions (p, y), (p, ay) are used occasionally for the depth-profile. 

NRA gives information about the depth distribution of elements where a nuclear reaction can occur. One reaction often used for the profiling of hydrogen is N ( j, ay)C - at a resonance energy of 6..38S MeV (97]. The detection limit for the ub.solule elemental concentration is 0.1 to I at. %. In special cases the detection limit can be extended to lower concentratioas using standards of known composition. The detection limit for hydrogen using trace analysis techniques is currently 10 ppma (98). 

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