PIXE-STIM microtomography: Zinc and manganese concentrations in a scorpion stinger

Abstract

Microtomography using PIXE (proton induced X-ray emission) is developed and applied. Iterative algorithms for emission tomography (Donner algorithms) are modified for this purpose. STIM (scanning transmission ion microscopy) microtomography provides the required local X-ray attenuation factors and X-ray production cross sections (σ x's). The variation in σ x is treated along with X-ray attenuation in an effective attenuation factor. Several criteria for the optimal number of iterations are discussed. Element density values obtained from PIXE tomography are normalized with density values from STIM tomography to provide local concentration values. Three transverse sections of the sting of a scorpion, Hadrurus arizonensis, are reconstructed tomographically. Local zinc concentrations reaching as high as 25(± 3)% of dry mass are found. Manganese concentrations reaching 3.8(± 0.5)% of dry mass are also found. In the section manifesting high concentrations of both manganese and zinc, the zinc is found mainly in a band beneath the manganese-rich surface layer. Specimen damage during PIXE is found not to have significantly affected the results.