European Journal of Scientific Research (ISSN: 1450 ... - EuroJournals

© European Journal of Scientific Research, Vol 7, No 5, 2005
controlled MCA coupled with a standard electronic chain was used for the data acquisition and
the storage of the energy spectra. The other details of the experimental set up for routine PIXE
analysis at this laboratory have been reported [4,5]. For the analysis, the recent approach of
Balzan et al [6] was adopted where every sample was bombarded twice for the lower and higher
energy sections of the spectrum without damaging the samples. An 80 µm thick aluminum
absorber was placed in front of the Si (Li) detector to remove X-rays with low energies, thereby
enhancing the sensitivity of the heavy elements. The beam currents of between 70 and 100 nA
were conveniently used here without any negative effects on the performance of the detector due
to high counting rates. This produced the high energy part of the spectrum. Similarly, for the low
energy section of the spectrum, a 250 um thick Mylar funny filter with 3.3 % hole was used. Here
the beam currents of 5 to 20 nA were used, and the dead time was generally below 10%. The
stored X-ray energy spectra were later analyzed using the computer code GUPIX [7] leading to
elemental concentrations of the muscovites.
RESULTS AND DISCUSSION
The major element data and trace element data on the muscovites are presented in Tables 1 and 2.
The results of PIXE analysis of the samples together with their corresponding standard deviations
are presented in Table 2. Our results were in very good agreement with the certified values of the
geological standards and hence establish the reliability of the data. Electronprobe data ( Ige
unpublished Table 1) shows that the investigated white micas are phengites to nearly pure
muscovites with compositions as shown by the following contents (in atoms per formula unit) Si
= 6.15 - 6.18; Ti = 0.004 - 0.09; Al tot = 5.29 - 5.44; Fe tot =0.31 – 0. 32; Mg = 0.12 - 0.13, Na=
0.25-0.32, whilst K= 1.44-1.61. The approximate muscovite calculated formula (Al1.9 K0.8
Fe0.15Mg0.1 O12 Si3.1) and conforms with muscovites used as electrical insulator [7, 8].
The PIXE data on trace elements shows that concentration of elements are variable even within
samples. K contents vary between 1.6 and 6.3% Ca content ranges between 97 and 510 ppm
whilst V value ranges between 8 and 22ppm. Ti concentration ranges between 15 and 82ppm
whilst V value generally ranges between 13 and 23 ppm. Mn ranges between 185 and 636 ppm
with majority of the data falling in the 280 and 350 range. The Fe contents range between 0.78
and 1.05%. More than half of the samples showed the concentration of cobalt between 18 and 26