This article throws light upon the top five techniques of ion beam analysis in monitoring pollutants. The techniques are: 1. Particle (Proton) Induced X-Ray Emission Analysis 2. Particle (Proton) Induced Y-Ray Emission Analysis 3. Proton Elastic Scattering Analysis 4. Rutherford Backscattering Spectrometry 5. Elastic Recoil Detection Analysis.
Technique # 1. Particle (Proton) Induced X-Ray Emission Analysis (PIXE):
PIXE is a powerful and relatively simple analytical technique that can be used to identify and quantify trace elements typically ranging from Na to U. Sample irradiation is usually performed by means of 2-3 MeV protons produced by an accelerator. X-ray detection is usually done by energy dispersive semiconductor detectors such as Silicium (Lithium) or High purity Germanium detectors.
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This multi-elemental analysis technique can measure more than 30 elements in short time due to higher cross-sections as compared to XRF. With the addition of PIGE and PESA, IBA allows for the detection of light elements that is useful for finger printing, sources apportionment and estimation of organic carbon. Typical detection limits range from 1 to 50 µg m-3.
The remaining three methods are used simultaneously to achieve additional information on elements that cannot or hardly be measured with PIXE.
Technique # 2. Particle (Proton) Induced Y-Ray Emission Analysis (PIGE):
When a charged particle (typically protons) approaches the nucleus of a target atom, the Coulomb force usually repels it. However when the incident particle has enough energy to overcome the repulsive Coulomb force a charged particle then penetrates through the electrostatic barrier into the nucleus, resulting in interaction with the nuclear forces.
During that process, a number of interactions occur, depending on the energy of the incident particle and the type of target nucleus. Typically, a nuclear reaction will occur, resulting in the emission of high energy x-rays (x-rays emitted from nucleus are for historical reasons called gamma rays) and other nuclear particles.
In the case of PIGE technique, emitted gamma rays are of particular interest as their energies are characteristic of the element and are therefore used to fingerprint elemental composition while yields are used to quantify element concentration. The detection of the emitted gamma rays is usually done by large volume Ge detectors.
Technique # 3. Proton Elastic Scattering Analysis (PESA):
PESA is similar to Rutherford backscattering analysis (RBS) but in forward direction and in used to measure H2 to help to distinguish between elemental and organic carbon in samples Hydrogen in the air particulate matter collected on a filter can be measured providing the filter material is free of hydrogen.
Technique # 4. Rutherford Backscattering Spectrometry (RBS):
In RBS, only backscattered ions are detected, and backscattering can only occur if the target atom’s mass is heavier than that of the incident ion. RBS allows the measurement of C, N and O mainly. This information is mostly useful for charge calibration purposes.
Technique # 5. Elastic Recoil Detection Analysis (ERDA):
ERDA is the measurement of recoiling atoms following elastic nuclear collisions at a glancing angle. ERDA is the complementary technique to RBS and is used mainly for profiles of very light ions such as hydrogen or deuterium in thin layers, and in the near surface region of materials.
ERDA is a popular technique for the determination of hydrogen in solids, and studies of polymer inter diffusion, but less so in environmental monitoring.