Abstract
The method of cyclic neutron activation analysisis is selective in enhancing the signal-to-noise ratio of short-lived nuclides in the matrix when compared with the conventional method. The general theory is presented and serves as the basis for this work. The statistics appropriate for counting short-lived activities are explained. A brief description of irradiation facilities and determination of the neutron fluxes therein, corrected for flux depression, self-shielding and edge effects, follows. The detectors used are properly calibrated with regards to energy and the counting geometry and an empirical formula is derived to correct for the finite size of the detectors. Scanners and source holders were designed and constructed for the study of Ge(Li) detector characteristics. In addition, Monte Carlo techniques are used to determine the solid angle subtended at the detector by an extended source and the non uniformity, of the detector sensitivity is incorporated. The usefulness of thermal and epithermal cyclic activation analyses A is demonstrated. The sensitivities and cadmium ratios of a dozen elements which produce short-lived isotopes on irradiation, the calculation of detection limits for a number of elements in various biological and environmental standard matrices and the measurement of half-lives of short-lived fission products of natural uranium, which serves as a means of identification and confirmation of their presence in complex gamma-ray spectra, illustrate these. The absolute method of analysis is employed in the determination of elemental concentrations in reference materials, contaminated soil samples and plants suspected of containing high concentrations of uranium. Prompt gamma-ray analysis employing Ge(Li) detector in anti-coincidence mode with a NaI(Tl) scintillator and applied quantitatively to the determination of elemental composition of both fresh and old human bones, demonstrated the capabilities and limitations of the technique.