Rutherford Backscattering Spectrometry and Nuclear Reaction Analysis

Abstract

The RBS (Rutherford backscattering spectrometry) and NRA (nuclear reaction analysis) are a subset of what is generally known as ion beam analysis (IBA) methods, performed with energetic (typically a few hundred keV to a few MeV) ion beam from accelerators. The energies involved render the measurements insensitive to molecular or atomic shell effects, and thus chemical effects. RBS is based on elastic Coulomb scattering between the projectile and the target nuclei, and is usually applied to obtain data for most if not all elements present in the specimen. In contrast, NRA is based on nuclear reactions which are element specific. The most commonly used beam in RBS is He⁴ (alpha particles) with 1–4 MeV energies. Protons are also used for RBS, typically with energies between 100 keV and 2 MeV, but the beam is more suited for NRA applications. The methods are non-destructive, and provide the elemental composition and/or structure, namely the depth profiles from the surface region spanning the first few hundred layers of atoms to up to 10 μm depth. Beyond this, complications due to straggling effects result in loss of sensitivity and/or of depth resolution. At very low energies, the effect of screening of the atomic electrons must be taken into account and this is covered in another section. The main advantages of the methods are the rapidity of analysis (few minutes), and the direct and simple way the information can be obtained from the data. The methods are amenable to simple calibration procedures to facilitate quantitative, standardless analysis.