Worldwide measurement of radon flux on mine tailing dams has been performed
using various instruments. Some of the methods used in South Africa are electrets,
alpha tracks, accumulator cans etc. Although these techniques and methods have
been used for many years, a number of shortcomings are still evident. The major
shortcomings are that, the methods lack spatial representivity that is, they only
measure the radon flux at a point where they' are placed and not the whole site in that
way, the spatial variation is not shown in a site which is not homogeneous. Another
shortcoming is that, they do not show seasonal variation and some have a back
diffusion problem, and the time required for the result to be known is too long. For·
example it takes several days for electrets to gather sufficient information required,
yet it is a single point result. This makes it difficult to steer the measurement.
Furthermore, the moisture and atmospheric pressure on the mine dump influence
some of the measurements.
The above shortcomings led to the investigation of a new· technique based on
gamma ray spectrometry to quantitatively assess the radon flux from the mine
tailings dam. The system is called Multi Element Detector for Underwater Sediment
Activity (MEDUSA). Initially, this technique was uniquely designed to measure the
radioactivity on the sea floor where it proved to be successful. The major focus of
this research study was, therefore, to critically assess the MEDUSA gamma ray
detector system for measurement of radon flux on a tailings dam.
The process of determining the radon flux in this work involved field measurements
using MEDUSA and laboratory measurements using Hyper Pure Germanium (HPGe}
detector. The laboratory measurements were for correcting the field measurements.
The HPGe has better advantage over MEDUSA in terms of resolution and this
means that the gamma ray energy peaks have better visibility than on the MEDUSA.
The field measurements on the tailings dam were done using the MEDUSA mounted
on a 4x4 vehicle, and simultaneously sample points were identified and samples
collected.
The samples were measured for specific activity in the laboratory using gamma
spectrometer with HPGe detector. These measurements enabled the determination
of a factor that was used to calculate the activity of radium in the field. This activity
was found to have an average of 309 Bq.kg"1 with data range of 60 -540 Bq.kg-1.A radon flux equation was then derived and used to calculate the radon flux on the field. Based on the radium content, the radon flux was calculated to average about 0.105 ± 0.023 Bq.m-2 .s-1
The results are within the same range as the previous flux measurement on the
same tailings dam but with better statistics. This research work has demonstrated
that the MEDUSA can be adapted for radon flux determination from tailings dam. The
method promises to address some of the key shortcomings of existing techniques
and the usefulness of this method can be extended to measuring radioactivity on
contaminated sites for rehabilitation purposes. / Thesis (MSc. ARST) North-West University, Mafikeng Campus, 2003
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nwu/oai:dspace.nwu.ac.za:10394/11321 |
| Date | January 2003 |
| Creators | Motlhabane, Tebogo Gladys Kgaugelo |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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