A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy, School of Physics. Johannesburg, 2017. / Accelerator Mass Spectrometry (AMS) is an ultra-sensitive isotopic analysis technique
that allows for the determination of isotopic ratios of rare long-lived radionuclides such as
radiocarbon. AMS has become an important tool in many scientific disciplines, due to its
sensitivity of detecting isotopic ratios at the level of 10-15 by making use of nuclear physics
techniques and methods.
The objective of the present work was to design and implement a new AMS system at
iThemba LABS, the first of its kind on the African continent. The system is described in detail
along with the relevant ion optics simulations using TRACE-3D. Beam optics calculations
were performed for carbon isotopes, using the TRACE-3D code, in order to optimize the design
of the new spectrometer and assess its overall performance.
The AMS technique was applied in two unique South African research projects in
relation to archaeology and environmental air pollution studies. The AMS technique, combined
with the Proton-Induced X-Ray Emission (PIXE) technique, was also applied in an
environmental study with respect to the contribution of contemporary and fossil carbon in air
pollution in the Lephalale District, close to both the newly built Medupi coal-fired power
station (~5 GW, the largest ever build in South Africa), and the existing Matimba coal-fired
power station.
The discrimination of contemporary carbon and fossil carbon is accomplished by using
the AMS technique in measurements of the 14C/C ratios of aerosol particulate matter. The
absence of 14C in fossil carbon material and the known 14C/C ratio levels in contemporary
carbon material allows us to distinguish between contemporary carbon and fossil carbon and
decipher in this manner different anthropogenic contributions.
iv
The contemporary carbon throughout our sampling campaign in the Lephalale District
has been measured to be approximately 53% of carbon aerosol. As many studies have been
performed of contemporary carbon and fossil carbon, no other contemporary and fossil carbon
source assessment method provides the definitive results that can be obtained from radiocarbon
measurements.
PIXE analysis for the determination of the elemental composition of particulate matter
in samples near the Medupi coal-fired power station in the Lephalale District was also
performed for 6 elements, namely, K, Ca, Ti, Mn, Fe, and Zn. In the samples that were analyzed
the particulate matter concentrations did not exceed the air quality standards regulation at
Lephalale. The recommended daily limit air quality standard by South African legislation is 75
µg/m3.
Enrichment Factor (EF) analysis of soil with respect to Fe shows anomalously high
values for Zn.
AMS was also applied to archaeological studies of early herding camps of the khoe
khoe people at Kasteelberg, situated on the southwest coast in South Africa, and are among the
best preserved sites of their kind in the world. Sea-shell samples from the Kasteelberg B (KBB)
site have been dated with AMS at Lawrence Livermore National Laboratory (LLNL) in an
effort to elucidate the relationship between the herder-foragers of the inland and shoreline sites
in terms of migration patterns. The radiocarbon dates obtained are in general agreement with
the other studies that have been performed on the site, and show that the ages of artifacts are
less than 2000 years. The samples for this study originate from various well defined
stratigraphic-levels at square A3 at KBB. It was evident from excavation that the artefacts seem
to be of the same period and there is no evidence of mixing from different stratigraphic layers.
v
Radiocarbon dates were calibrated using Calib 6.1 and each was corrected for marine
reservoir effect. The date range between the earliest and most recent dates that were obtained
span gap is approximately 400 years from AD 825 to AD 1209. The majority of the radiocarbon
dates of the KBB site belong to dates of 1002-1100 AD, the other few belong to 825-958 AD,
and the last single date of 1209 AD. The new AMS dates from this work suggest the high
probability that indeed there was a hiatus between the two occupations designated as lower and
the upper KBB. The significant changes seen in material culture styles as well as in the nature
of occupation and change in accumulation rate of deposits therefore do not necessarily indicate
a cultural replacement caused by the arrival of a new population. This implies that the
occupants of lower KBB may also have been Khoe-speakers, and not local San. / GR2018
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/23750 |
| Date | January 2017 |
| Creators | Sekonya, Kamela Godwin |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (xv, 197 leaves), application/pdf |
Page generated in 0.0025 seconds