A dissertation submitted to the Faculty of Science University of the Witwatersrand, Johannesburg, for the Degree of Master of Science. / The method of activation analysis is extended to the analysis of very large samples (up to 1kg) of ores and minerals. The use of such large samples has two advantages: first, the sensitivity of the method is greatly increased, and secondly, inhomogeneity of distribution and hence sampling problems are greatly reduced. Samples are used without any kind of treatment and the method is non - destructive. There are also disadvantages associated with the use of large samples. Absorption effects (both of neutron and y - rays) become important and as a result the calibration curves are influenced by the bulk density and composition of the samples. In certain cases, the calibration curves may also be non - linear. These effects have been studied in detail for the determination of gold, through the reaction 198Au(n,y)l98Au. After irradiating various samples of known concentrations of gold, calibration curves for gold in gold ore and carbon samples have been established. The effect of y -ray and neutron absorption has been studied in carbon samples using either thermal or epithermal neutrons and the optimum sample thickness has been established. In addition, the curve for the optimum decay time has been obtained for gold in ore samples. Based on the experimental results, a theoretical model has been applied to study the variation of the statistical error with the various factors involv~d, i.e. irradiation, decay, counting times, source strength and sample size. It has been also used to analyse theoretically the results for the optimum thickness and the variation of the background under the 411. 8 keV peak of Au-198. Further work has been undertaken to investigate whether the method can be used to determine elements from the platinum group which are much less active than the gold. Gamma ray peaks from Ir - 192, Au - 199, Pt - 199 Rh - 104m and Os-193 could be identified and possibly from Pd-109. Further work is necessary to study each element separately. In the case of gold, very satisfactory results were obtained. It is too early to state that it provides a replacement for the fire - essay method for gold, but the potential definitely exists. / Andrew Chakane 2021

A method for the determination of low concentrations (<10PPM) of rare earths in minerals and rocks by neutron activation analysis is presented. A 10 min irradiation of sample and standard required no chemical purification owhile a 20hr, irradiation required an ion exchange purification before actual counting. A Li-drifted germanium detector an 1600 channel gamma spectrometer provided sufficient resolution to allow determination of La, Pr, Sm, Eu, Dy, Ho, Yb and Lu in two apatite samples. The results are generally higher than those obtained by other neutron activation analyses. The specific causes are uncertain and can be resolved best by further study and modification of this neutron activation analysis. / Thesis / Bachelor of Science (BSc)

A fast pneumatic transfer facility was installed at the Nuclear Engineering Teaching Laboratory (NETL) of the University of Texas at Austin for the purpose of cyclic thermal and epithermal neutron activation analysis. In this work efforts were focused on the evaluation of cyclic epithermal neutron activation analysis (CENAA). Various NIST and CANMET certified materials were analyzed by the system. Experiment results showed 110Ag as one of the isotopes favored by the system. Thus, the system was put into practical application for identifying silver concentration in the Arctic atmospheres in air filters collected in 2009, and traces in metallic ores Comparison of silver concentrations via CENAA with the CANMET certified reference materials gave very good results. / text

A prompt-gamma, neutron-activation analysis facility earlier developed at the Nuclear Science Center of Texas A&M University could not be used successfully to analyze geologic samples due to high detection background, low neutron fluence rate and poor detection equipment . A systematic investigation into the performance capability of a prompt-gamma, neutron activation analysis facility was undertaken in this research project. The facility was reconstructed and used to obtain prompt-gamma spectra of chlorine and cadmium and from the spectra, the net peak area counts for the most intense prompt-gamma-ray energies were obtained. A theoretical model was developed which can predict the net peak area counts expected on these prompt-gamma-ray energies using the thermal neutron fluence rate at the sample position, the absolute efficiency of the detector, and the mass and partial gamma-ray production cross section data for the samples. The experimental and predicted results were compared to establish the performance capability of the reconstructed facility. Good agreements between experimental and predicted results were obtained for chlorine, but results from cadmium showed larger discrepancies due to self-shielding effects. Corrections for self-shielding effects were applied to results from cadmium and the experimental and predicted results were also in good agreement. The satisfactory results indicate that it is possible to implement the prompt-gamma, neutron-activation analysis technique at Beam Port #1 of the Nuclear Science Center Reactor. To be able to obtain excellent results from other samples, improvements in shielding materials to attain a lower detection background and a highly efficient detection system should be incorporated.

A prompt-gamma, neutron-activation analysis facility earlier developed at the Nuclear Science Center of Texas A&M University could not be used successfully to analyze geologic samples due to high detection background, low neutron fluence rate and poor detection equipment . A systematic investigation into the performance capability of a prompt-gamma, neutron activation analysis facility was undertaken in this research project. The facility was reconstructed and used to obtain prompt-gamma spectra of chlorine and cadmium and from the spectra, the net peak area counts for the most intense prompt-gamma-ray energies were obtained. A theoretical model was developed which can predict the net peak area counts expected on these prompt-gamma-ray energies using the thermal neutron fluence rate at the sample position, the absolute efficiency of the detector, and the mass and partial gamma-ray production cross section data for the samples. The experimental and predicted results were compared to establish the performance capability of the reconstructed facility. Good agreements between experimental and predicted results were obtained for chlorine, but results from cadmium showed larger discrepancies due to self-shielding effects. Corrections for self-shielding effects were applied to results from cadmium and the experimental and predicted results were also in good agreement. The satisfactory results indicate that it is possible to implement the prompt-gamma, neutron-activation analysis technique at Beam Port #1 of the Nuclear Science Center Reactor. To be able to obtain excellent results from other samples, improvements in shielding materials to attain a lower detection background and a highly efficient detection system should be incorporated.

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