Scanning Microscopy


When an ion beam in the energy range of a few MeV/amu impacts on a mineral, visible light can often be observed. This light, termed ionoluminescence (IL), has been shown to be a very useful tool for investigating geological specimens when it is combined in a nuclear microprobe with a well-established, quantitative, trace element method such as Particle Induced X-ray Emission (PIXE). When plagioclases from the Skaergaard intrusion, East Greenland, were irradiated with protons, bluish luminescence was observed. Spectroscopic IL studies were undertaken with 1.5 and 2.5 MeV protons with power densities ranging from about 6 to 160 W/cm2. In the IL spectra of the plagioclase specimens, four emission bands were observed, peaking at about 4200, 4600, 5500, and 7500 A, respectively. The relative intensities of the emission bands in the short wavelength region were rather constant for all samples, except for the long wavelength band, activated by Fe3+ and peaking at 7500 A, which varied considerably. Variation in the oxidation states of the samples was investigated by measuring the Fe3+ intensity from IL normalized to the total iron concentration as obtained by PIXE. The relationship between the Fe3+-activated peak area normalized to the total iron content and the expected relative oxidation state was found to be relevant.

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