Application of neutron and proton induced prompt emissions for elemental analysis.

The principles of neutron and proton induced reactions and their application to elemental analysis are described. Prompt Gamma-ray Neutron Activation Analysis (PGNAA) as a relatively rapid technique for the determination of trace amounts (ppm) of B and Cd is given. The need to establish the absolute method of analysis is investigated through the evaluation of the K-factor which acts as a monitor on the reliability of the various parameters involved in the absolute method. The neutron flux and detector efficiency are characterised and flux non-uniformity and detection efficiency for extended sources are discussed through the development of a Monte Carlo technique which enables us to calculate the geometric and effective solid angles subtended by a collimated detector at cylindrical and disc shaped sources or targets. Use of protons with energies ≤ 2 MeV to induce nuclear reactions which emit prompt alpha particles and gamma-rays is applied to the elemental analysis of various matrices. Although this technique is a surface and near surface analysis, it serves to confirm the results obtained by PGNAA as well as to indicate the non-uniformity of the elemental distribution along the sample surface scanned. This is demonstrated for a number of plant samples and a human tooth enamel. Detection of prompt alpha particles emitted necessitates the use of absorber foils to stop the high flux of backscattered protons from reaching the alpha detector. The broadening the introduction of such foils cause to the measured alpha spectra is also experimentally determined