Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Non-destructive portable X-ray Fluorescence (pXRF) and Particle Induced X-ray
Emission (PIXE) were used to measure the elemental concentration of rock art
fragment paintings. For pXRF the Amptek Silicon Drift Detector (SDD) and Niton
XL3t spectrometers were used to perform the measurements. These two
spectrometers use different spectrum analysis methods. The Peak Deconvolution
(PD) analysis method is used for the Amptek SDD and an Inverse Overlap Matrix
(IOM) method is used for the Niton XL3t spectrometer.
The pXRF methods were validated by using alloys, coins and rock standards. The
validation is important to establish if the pXRF technique is properly understood and
used and to advance the investigation to more complex rock art paintings, with
heterogeneous and layered properties. The elemental concentrations obtained for
the Standard Reference Materials (SRMs), which were used for the validation, were
in good agreement with that of the known concentration of the SRMs.
The two rock art fragments which were analysed from the Mount Ayliff and Ha
Khotso caves were part of larger rock art painting prior to it being naturally exfoliated
from the rock. For the Mount Ayliff rock art, seven paint points, two unpainted rock
(varnish) point adjacent to the paint and the back of the rock were analysed. The
colour of the paint ranged from black, shades of brown and shades of red. The black
paint is due to manganese or charcoal. The red colour is due to iron oxide and the
red-brown colour is due to Hematite (a type of ferrous oxide) [1]. For the Ha Khotso
fragment the paint on the front of the rock and the rock substrate (back of the rock)
were analysed.
For the Mount Ayliff rock art fragment the results for both pXRF spectrometers
indicated that the elemental concentration was uniform across the fragment. This is
due to the formation of a uniform layer of minerals such as silica and calcium
introduced by the seepage of water through the cracks of the cave. Therefore no
correlation could be established between the colour of the rock art paint and the
elements detected, as was found with the work done by Peisach, Pineda and
Jacobson [1]. For the Ha Khosto rock fragment a relation between the Ca
composition and the cream colour of the rock art paint was established. Both the
PIXE and pXRF techniques were used to identify the compound concentrations of
the Ha Khotso rock art fragment. The comparison between the two techniques
highlights the complexity of rock art paint analysis. The results from the PIXE
elemental mapping indicated the non-uniform distribution of the elements in the
analysed region. From the rock art fragment measuring the analysed points 5 times and obtaining the
same results, indicated that the particle size and inhomogeneities did not have much
effect on the compound compositions.
In order to obtain high accuracy results with pXRF, sound scientific methodology with
specific knowledge and expertise, not only about the XRF technique, but also about
the sample under investigation is required. For alloy analysis pXRF is well suited, the
analysis of geological material however more complex, since they are composed
predominately of low atomic elements e.g. silicon, aluminium, magnesium, sodium,
oxygen and carbon – all of which are excited with very low efficiencies. / AFRIKAANSE OPSOMMING: Nie-beskadigended X-straal Fluoresensie (pXRF) en Deeltjie Geinduseerde X-straal
emmissie (PIXE) was gebruik om die elementêre konsentrasie van die rotstekeninge
in hierdie studie te bepaal. Vir die pXRF-tegniek is die “Amptek Silicon Drift Detector
(SDD)” en die “Thermo Scientific Niton XL3t” spektrometers gebruik gemaak om die
metings uit te voer. Die twee spektrometers maak gebruik van verskillende spektrum
analiseringsmetodes.Die “Peak Deconvolution (PD)” analiseringsmetode is gebruik
vir die “Amptek SDD” en die “Inverse Overlap Matrix (IOM)” analiseringsmetode is
gebruik vir die “Thermo Scientific Niton XL3t” spektrometer.
Vir die validasie van die pXRF-metode is van allooie, muntstukke en rots
standaarded gebruik gemaak. Die validasie is belangrik om vas te stel of die pXRF
tegniek behoorlik verstaan en gebruik word en om die ondersoek te bevorder na
meer komplekse rotstekeninge, met heterogene en lae eienskappe. Die element
konsentrasies wat vir die “Standard Reference Material (SRM)” wat gebruik is vir die
validasie, was in 'n goeie ooreenkoms met die van die konsentrasie van die SRM,
wat bekend is.
Die twee rotstekeninge wat ontleed is van die Mount Ayliff en Ha Khotso grotte en
was deel van 'n groter rots kuns skildery voordat hul natuurlik afgebreek het. Vir die
Mount Ayliff rotskuns, is sewe verf punte, twee ongeverfde rots (vernis) punte
aangrensend aan die verf en die agterkant van die rots ontleed. Die kleur van die
verf het gewissel van swart, skakerings van bruin en skakerings van rooi. Die swart
verf kan toegeskryf word aan mangaan of houtskool. Die rooi kleur is as gevolg van
ysteroksied en die rooi-bruin kleur is as gevolg van Hematiet ('n tipe van yster
oksied) [1]. Vir die Ha Khotso rotskuns is die verf aan die voorkant van die rots en
die rots substraat (agterkant van die rots) ontleed.
Vir die Mount Ayliff rotstekening het die resultate vir beide pXRF spektrometers
aangedui dat die elementele konsentrasie uniform oor die rotstekening is. Dit is as
gevolg van die vorming van 'n uniforme lagie van silica en kalsium, wat deur die
sypeling van water deur die krake van die grot na die oppervlak van die rotstekening
beweeg het. Daarom kon geen korrelasie tussen die kleur van die rotstekening en
die elemente wat gemeet is bepaal word nie, soos gevind deur die werk van
Peisach, Pineda en Jacobson [1]. Vir die Ha Khotso rotstekening is ‘n verband
tussen die room kleur van die rotstekening verf en Ca konsentrasie gevind. Beide die
PIXE en pXRF tegnieke is gebruik om die konsentrasies van die Ha Khotso
rotstekening te identifiseer. Die vergelyking tussen die twee tegnieke beklemtoon die
kompleksiteit van rotstekening verf analise. Die resultate van die PIXE elementele
karakterisering het aangedui die nie-eenvormige verspreiding van die elemente in
die ontlede area. Deur die meting van die ontlede punte 5 keer te herhaal, en dieselfde resultate
verkry, is ‘n aanduiding dat die deeltjie grootte en inhomogeniteite nie veel invloed
op die elementele konsentrasies het nie.
Ten einde 'n hoë akkuraatheid resultate te kry met pXRF, moet goeie wetenskaplike
metode toegepas word met spesifieke kennis en kundigheid, nie net oor die XRF
tegniek, maar ook oor die rotstekening wat ondersoek word vereis. pXRF is wel
geskik vir die ontleding van allooie, die ontleding van geologiese materiaal is egter
meer kompleks, aangesien die materiaal hoofsaaklik bestaan uit lae atoomgetal
elemente bv silikon, aluminium, magnesium, natrium, suurstof en koolstof - wat almal
met lae doeltreffentheid opgewek en baie afgerem word in die materiaal.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/86541 |
| Date | 04 1900 |
| Creators | Steyn, Ruan |
| Contributors | Papka, Paul, Pineda-Vargas, Carlos, Stellenbosch University. Faculty of Science. Dept. of Physics. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xvii, 86 p. |
| Rights | Stellenbosch University |
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