Abstract
The principles of Instrumental Neutron Activation Analysis (INAA) techniques and their applications in bulk analysis making use of prompt and delay gamma-rays have been outlined. Bulk analysis has the advantage of reducing sample preparation, and the use of large volume samples ensures that the analyses are representative of the bulk. A full description of the irradiation facility with the changes in terms of better shielding, and the use of a microcomputer in cycling the neutron source and the acquisition system control which is employed for simultaneous prompt and cyclic NAA has been given. The absolute method was used in the analysis of different environmental materials as bulk samples (2-5 kilogrammes) including sawdust, landfill, coal and fly ash. This means that all the parameters involved in the activation equation should be known. In particular, it was important to evaluate the solid angle between the sample and the detector and relate its variation to the detector absolute efficiency. For that purpose a Monte Carlo program was developed to find the effective solid angle subtended by a collimated detector for irregularly shaped bulk samples. The program was tested experimentally using an 152Eu voluminous source and the results showed a variation of not more than 4 % between the measured and calculated absolute efficiencies. INAA based on a 5 Ci (1.85x1011 Bq) Am-Be neutron source and the absolute method with the necessary corrections for neutron and gamma-ray attenuation showed to be most useful in determining the concentrations of elements such as H, B, C, O, Al, Si, S, Cl, Ti and Fe in different environmental bulk samples. Other elements such as F, Na, Mg, K, Ca, V, Mn, Cu, Zn, Se, Br, Ag and In may also be analysed if found in high concentrations. INAA based on a nuclear reactor and proton induced X-ray emission (PIXE) analysis based on a 2 MeV Van de Graaff accelerator were employed in this study as trace elements techniques using the comparator method. The concentrations of the elements and the associated detection limits in these samples were given and a comparison was made for those elements commonly obtained in both techniques. Finally, the effect of hydration of samples on the sensitivity of ten elements has been investigated. It was found that with an increased amount of water added (i.e. an increase in the amount of hydrogen present in the sample) to the sample matrix, an increase in elemental sensitivity was observed up to a certain value after which it remains more or less constant. Sensitivities of elements were determined over broad ranges of H concentrations with constant sample volume and shape in order to gain an understanding of the process(es) responsible for the enhancement.