Ion beam analysis - recent developments and future prospects

Full text: The use of particle accelerators for analytical purposes has significantly developed over the last decades. Compact, dedicated and commercially available electrostatic accelerators have been installed in many laboratories all over the world, mainly intended for use with nuclear analytical techniques. The applications are numerous in many fields. Access to an accelerator is not entirely necessary for IBA since also alpha-emitting radioactive sources can be used. Although the intensity of ions will be orders of magnitude lower special situations, such as that of the space expedition to Mars, source-excited IBA can play an important role. The term ion beam analysis (IBA) is normally reserved for the use of MeV ions, often protons, deuterons or alpha particles, to induce reactions suitable for elemental and structural characterisation. Sometimes techniques, such as the sputtering technique SIMS, using lower energy particles could also be included. In this presentation some of the more important techniques will be presented with some indications of common applications and their future developments. MeV ions impinging on materials have a high probability of ejecting inner shell electrons resulting in a high probability for emission of characteristic x-rays, being utilised in the PIXE-technique (Particle-Induced X-ray Emission). Particles can also be scattered by Coulomb interaction with the nucleus, in classical Rutherford mode or other non-Rutherford scattering mode. The scattered particles is detected, analysed and used in Backscattering Spectrometry, often imprecisely denounced RBS (Rutherford Backscattering Spectrometry). Except for special nuclei and ion energies the probability for ion-induced nuclear reactions is normally quite low at the energies in question. However, for specific isotopes it can be used in nuclear reaction analysis or particle-induced gamma-ray emission. In a newer version, photon-tagged NRA, the signal-to-background ratio is significantly enhanced by the use of fast electronics coincidence measurements. Many applications require analytical procedures applicable to microscopic structures and the ion intensity will then often be low. The high interaction cross sections for RBS and PIXE make these techniques ideal to use in such device. pNRA can also be used with such low ion beam currents. The nuclear microprobe is an instrument combining these techniques a high spatial resolution beam with, imaging methods such as scanning transmission ion microscopy (STIM), secondary electron imaging (SEI) and ionoluminescence (IL). The nuclear microprobe hence constitutes a powerful tool for characterisation of microscopic specimens and has significantly extended the use of ion beam analysis. In addition to previously described analytical methods there are also techniques based on recoiling particles ejected during particle bombardment. Elastic recoil detection analysis (ERDA) is one such example allowing for depth distribution of shallow impurities in materials. In particular, hydrogen distribution is very interesting to investigate with this technique. Also heavier, high energy ions can be used for such studies. The development of new, more sophisticated ion irradiation methods and new means of detection of radiation has resulted and will result in new versions of existing techniques and also to new concepts of using IBA, today still not conceived. A brief indication of this development and of some very interesting applications will be presented