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Made available in DSpace on 2014-10-09T12:31:35Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:03Z (GMT). No. of bitstreams: 1 02234.pdf: 1681697 bytes, checksum: dd48c160c5cf8eb932f141d1bd7829e4 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

This thesis describes an investigation of the complex gamma-ray spectra accompanying the decay of iridium 192 and iridium 194. Precision energy measurements of twenty-one gamma-rays in Ir 192 and fourteen gamma-rays in Ir 194 have been made using the 50 cm. double focusing beta-ray spectrometer. In addition, the angular correlation function for the cascade gamma-rays of Ir 194 has been determined. A number of new radiations have been found In each spectrum and decay schemes are proposed for each nuclide. / Thesis / Master of Science (MS)

Adamantane <I>C₁₀H₁₆</I> is an interesting archetypal plastic crystal which has been extensively studied. It undergoes transition from a low temperature ordered phase to a high temperature disordered phase at T=208.6K. The <I>C₁₀H₁₆</I> molecule has tetrahedral symmetry and the orientational disorder to the plastic phase has been interpreted in terms of the distribution of the molecules between two equally preferred orientations. A molecular dynamics simulation of <I>C₁₀H₁₆</I> has been carried out using the CCP5 Library program <I>moliq-dynamo</I>, written by Dr. D Fincham of Keele University. The simulation model consists of rigid molecules interacting with an atom-atom pairwise additive potential. The dynamics of the adamantane molecules in the plastic phase have been investigated and results have been compared with previous work. The molecular trajectories generated by the simulation have been used to evaluate the intensity of diffuse x-ray scattering from the crystal. Results have been compared with experimental data obtained from energy-dispersive x-ray scattering measurements made at the Daresbury SRS. Using a series of simplified models of the crystal, the relative contributions to the scattered intensity from translational and orientational disorder have been investigated.

<p> Thermal neutron capture studies have been made of the odd-odd nuclei, 20F, 24Na, 28Al, 32P, 36Cl and 40K. The gamma ray spectra have been studied using a Ge(Li) pair spectrometer and revised decay schemes are presented for these nuclei. The Q-values and gamma ray multiplicities have been obtained for the reactions studied. The average partial widths for primary Ml and El transitions have been calculated for the six nuclei and compared with the theoretical estimates. The features of the capture gamma ray spectra are discussed and it is observed that for the six nuclei studied, the total intensity in the spectrum above the energy of 0.3 times the Q-value is nearly the same (~1.4 photons/capture).</p> / Thesis / Doctor of Philosophy (PhD)

<p> Contemporary approaches to data analysis suffer from being both time-consuming and subjective; however, the application of numerical techniques to the automated (non-interactive) analysis of gamma ray spectra often leads to considerably improved performance. The foundations and limitations of such techniques lie in the applicability of certain mathematical operations such as deconvolution, and the careful study of stochastic models. The use of digital filters as a method of enhancing detector response has been applied to a triple-coincidence counting arrangement, after modelling undesired physical effects. An objective background estimation method has been described based on the statistical nature of nuclear measurements. Finally, the application of such techniques is demonstrated with a package of FORTRAN programs designed to be used in a variety of situations with minimal modifications. </p> / Thesis / Master of Science (MSc)

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