Micro-PIXE 

  
µPIXE is based on the same principles as PIXE. The only difference is that the ion beam is focussed to a small spot size which is then raster-scanned across the sample surface. In this way a PIXE spectrum is collected for each raster point. From these spectra elemental maps can be constructed, showing the variation of the elemental concentrations across the sample surface. 
  
Applications: The µPIXE technique can be applied to a wide variety of sample materials. At ANSTO, µPIXE is often used for quantitative analysis in geology, biology, and environmental science.
   
For Example:
 
Metal hyper-accumulating plants 
 
Metal hyper-accumulating plants are a rare group of plant species that accumulate exceptionally high concentrations of metals in their above ground tissues, without showing symptoms of phytotoxicity. Quantitative localisation of the accumulated metals in the tissue is of considerable interest, because it helps to understand the eco-physiology of these plant species. In collaboration with various groups from Australian Universities the accumulation of heavy metals in different plant species has been investigated.
 
Micro-pixe_fig 1
The optical micrograph above shows a leaf section of Hybanthus floribundus prepared by freeze substitution. The outline of individual cells is clearly visible.

    

The figure below shows the elemental maps for Ca, Ni and K of the leaf section marked in the above micrograph.
 
 
Micro-pixe fig 2aMicro-pixe_fig 2Micro-pixe fig 2c
  
 
For comparison samples were prepared by freeze drying and the results are shown in the maps below. These maps show the elemental concentrations vary quite strongly in the different plant tissues, with high Ni concentrations in the epidermis as well as the vascular bundles. 
 
 
Micro-pixe fig 3a.jpgMicro-pixe_fig 3Micro-pixe fig 3c.jpg
 

  

upixe_fig 1

 

 

upixe_fig 2Micro-pixe_fig 4

 

Bivalve Mussel Shells 

 

Bivalve mussel shells were exposed to increased Mn concentration over a period of several weeks. 
 
The mussels were then released into a normal environment and accumulation and lag times of Mn were studied by using the Heavy Ion Nuclear Microprobe. 
 
Clear seasonal pattern in Mn concentration can be seen in the Figure to the right where the intensity of the blue colour is proportional to Mn concentration. 
 
In the figure to the right the corresponding micrograph of the mussel shell cross section is shown (size 3x10mm).
 
 
 
upixe_fig 3

 

upixe_fig 4
Figure: Results of uPixe analysis (top) with the corresponding micrograph of the mussel shell cross section; size 3x10mm (bottom)