The ''Q factor'' method: Quantitative microPIXE analysis using RBS normalisation

The main uncertainties in the absolute quantitation of PIXE elemental concentrations are the total deposited beam charge and the local matrix composition. This is particularly true in the case of microbeam PIXE analysis, where local inhomogeneities in the sample may affect both the secondary electron emission characteristics (and hence the recorded charge) and the PIXE yield. The use of simultaneous RES analysis can solve this problem in many cases. Provided the RES spectrum can be well modelled, its shape gives information on the local matrix composition, while the total area depends on the total beam charge. The ratio between the true charge and the measured charge (the ''q factor'') can then be used to normalise the PIXE data. Once the system is calibrated, standardless accuracy of 5-10% can be achieved in most cases. The method is described together with its limitations. Examples of the use of the method are presented.