Nuclear reaction analysis, element

Nuclear reaction analysis (NRA) is used to determine the concentration and depth distribution of light elements in the near sur ce (the first few lm) of solids. Because this method relies on nuclear reactions, it is insensitive to solid state matrix effects. Hence, it is easily made quantitative without reference to standard samples. NRA is isotope specific, making it ideal for isotopic tracer experiments. This characteristic also makes NRA less vulnerable than some other methods to interference effects that may overwhelm signals from low abundance elements. In addition, measurements are rapid and nondestructive. 

Nuclear reaction analysis (NRA) also identifies emitted particles which are different from the incident ones. In order to avoid permanent radioactivity, the energy of the projectile is maintained below 6 MeV, so that it is used primarily to determine the concentration and depth of light elements (Z < 9) in the near surface of solids. 

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). 

Mass determination by back scattered protons or STIM, light element detection by nuclear complementary techniques, e.g., back scattering (C,N,0), photon tagged nuclear reaction analysis, pNRA for detection of B, Li, Na... 

In the following, those ion beam analysis techniques that allow for fluorine detection will be presented. By far, the most important technique in this respect is nuclear reaction analysis (NRA). Although it can be rather complex to perform, it is the most often applied technique for fluorine trace element studies, due to a number of convenient and prolific resonant nuclear reactions which make it very sensitive to fluorine in most host matrices. NRA is often combined with particle-induced X-ray emission (PIXE) which allows for simultaneous determination of the sample bulk composition and concentrations of heavier trace elements. By focusing and deflecting the ion beam in a microprobe, the mentioned techniques can be used for two- or even three-dimensional multi-elemental imaging. 

The distribution of species normal to the surface can be obtained nondestructively by variation of the emission angle in XPS or AES (limited to a total depth of about 50 nm), by Rutherford backscattering spectrometry (applying only to elements with Z > 10) and by nuclear reaction analysis (Z < 20 only). Depth resolution in both RBS and NRA is in the range 5-50 nm. 

For the analysis of the new surface after every removal one may use all the surface techniques already mentioned in Sect. 4.3.1 as long as their information depth does not exceed the thickness of the layer removed Auger and ESCA-spectroscopy, secondary-ion mass spectrometry (SIMS), backscattering, ion-induced X-ray and nuclear reaction analysis. In addition, one may investigate the content of the element of interest in the removed layer. Because of the low absolute concentration of implanted ions most of the standard methods of analysis fail. The best results come from implantations of radioactive elements followed by measuring the radioactivity of the dissolved removed layer. 

NRA Nuclear Reaction Analysis Solids, thin films Mono-energetic Ions (LI, Be, B, etc.) 200 keV-6 MeV Protons, deuterons Ele, a-particles, y-rays 0.1-6 pm lOpm-IOmm Element Identification (all) detection llmll 10- M0- 47... 

NFE nonlinear finite element NRA nuclear reaction analysis... 

By nuclear reactions nonradioactive elements can be transformed to a radioactive species to enable their sensitive qualitative and quantitative determination (activation analysis). 

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)... 

Neutron Activation Analysis Few samples of interest are naturally radioactive. For many elements, however, radioactivity may be induced by irradiating the sample with neutrons in a process called neutron activation analysis (NAA). The radioactive element formed by neutron activation decays to a stable isotope by emitting gamma rays and, if necessary, other nuclear particles. The rate of gamma-ray emission is proportional to the analyte s initial concentration in the sample. For example, when a sample containing nonradioactive 13AI is placed in a nuclear reactor and irradiated with neutrons, the following nuclear reaction results. 

Although following similar nuclear reaction schemes, nuclear analytical methods (NAMs) comprise bulk analysing capability (neutron and photon activation analysis, NAA and PAA, respectively), as well as detection power in near-surface regions of solids (ion-beam analysis, IB A). NAMs aiming at the determination of elements are based on the interaction of nuclear particles with atomic nuclei. They are nuclide specific in most cases. As the electronic shell of the atom does not participate in the principal physical process, the chemical bonding status of the element is of no relevance. The general scheme of a nuclear interaction is ... 

Charged particle activation analysis (CPAA) is based on charged particle induced nuclear reactions producing radionuclides that are identified and quantified by their characteristic decay radiation. CPAA allows trace element determination in the bulk of a solid sample as well characterization of a thin surface layer. 

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