  A characteristic feature of the nuclear microprobe using a 3 MeV proton beam
is the long range of particles (around 70 \mu m in light matrices). The PIXE
method, with EDS analysis and using the multilayer approach for treating the
X-ray spectrum allows the chemistry of an intra-crystalline inclusion to be
measured, provided the inclusion roof and thickness at the impact point of the
beam (Z and e, respectively) are known (the depth of the inclusion floor is Z +
e). The parameter Z of an inclusion in a mineral can be measured with a
precision of around 1 \mu m using a motorized microscope. However, this value
may significantly depart from Z if the analyzed inclusion has a complex shape.
The parameter e can hardly be measured optically. By using combined RBS and
PIXE measurements, it is possible to obtain the geometrical information needed
for quantitative elemental analysis. This paper will present measurements on
synthetic samples to investigate the advantages of the technique, and also on
natural solid and fluid inclusions in quartz. The influence of the geometrical
parameters will be discussed with regard to the concentration determination by
PIXE. In particular, accuracy of monazite micro-inclusion dating by coupled
PIXE-RBS will be presented.
