Univ., Diss.--Saarbrücken, 2003.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2007. / Title from title screen (site viewed Feb. 22, 2008). PDF text: 178 p. : ill. ; 2 Mb. UMI publication number: AAT 3275068. Includes bibliographical references. Also available in microfilm and microfiche formats.

The excited states of Gd 154 obtained from the decay of Eu 154 have been investigated. Precise measurements of the energies and intensities of the gamma transitions have been made, using Lithium-drifted Germanium detectors. A revised decay scheme is presented in which all the gamma transitional energies agree with the corresponding energy differences between levels to within 1 Kev. A 1263.3 Kev level is established by the presence of a gamma transition of 892.7 Kev. Two other gamma transitions of energies, 903.6 Kev and 582.1 Kev from the negative-parity levels to the 2⁺ beta excited level have also been discovered. The proper locations of the 995.9 Kev and 1004.5 Kev in the decay scheme are confirmed by a gamma-gamma coincidence method using a Germanium detector and a NaI(Tl) scintillator. The energies and intensities of the internal conversion electrons and the beta transitions have been measured by an intermediate image spectrometer. Their values are quite consistent with the established decay scheme. Theoretical values of the energy levels and the branching ratios for gamma transitions have been calculated, using the Asymmetric Rotator Model (J.P. Davidson's treatment). The 'stiffness' parameter of the nucleus µ and its asymmetry parameter γ obtained are 0.402 and 11.52 degrees respectively. Comparison of the experimental and theoretical energies of seven positive-parity levels gives a root-mean-square deviation of 1.5 %. Three out of the four experimental branching ratios are in good agreement with the theoretical values. The monopole transition probability for the transition from the 0⁺ beta excited state to the 0⁺ ground state measured also agrees with the present theoretical calculation. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

No description available.

Graduation date: 1999

This dissertation focuses on the exploratory synthesis of compounds that contain R6ZI12 (R= Ce, Gd, Er; Z=Mn, Fe, Co, C2) clusters with the goal of finding magnetically interesting compounds. Several new compounds were made via high temperature, solid state methods and structurally characterized using x-ray diffraction. Compounds that contain isolated clusters were studied in order to understand the magnetic coupling between lanthanide atoms. The exploration of transition metal centered clusters resulted in the discovery of two new structure types, CsR(R6CoI12)2 (R=Gd and Er) and (CeI)0.26(Ce6MnI9)2. The xray crystal structure of CsEr(Er6CoI12)2 was solved in the Pa3 – space group with the cell length 18.063(2) Å at 250K (Z = 4, R1 [I>2σ(I)] = 0.0459). (CeI)0.26(Ce6MnI9)2 was made by combining KI, CeI3, MnI2 and Ce metal and heating to 850°C for 500 hrs. The single crystal x-ray structure for (CeI)0.26(Ce6MnI9)2 was solved in the trigonal, P3 – space group with lattice parameters of a = 11.695(1) Å c = 10.8591(2) Å (Z = 2, R1 [I>2σ(I)] = 0.0895). The magnetic susceptibilities of hexanuclear gadolinium clusters in the compounds Gd(Gd6ZI12) (Z = Co, Fe or Mn), CaxGd1-x(Gd6MnI12) and CsGd(Gd6CoI12)2 are reported. The single-crystal structure of Gd(Gd6CoI12) and CaxGd1-x(Gd6MnI12) are reported here as well. The compound with a closed shell of cluster bonding electrons, Gd(Gd6CoI12), exhibits the effects of antiferromagnetic coupling over the entire range of temperatures measured (4 - 300 K). Clusters with unpaired, delocalized cluster bonding electrons (CBEs) exhibit enhanced susceptibilities consistent with strong ferromagnetic coupling, except at lower temperatures (less than 30 K) where intercluster antiferromagnetic coupling suppresses the susceptibilities. Four new compounds containing Gd6C2 clusters have been found: Gd6C2I11, Gd(Gd6C2I12), CsGd(Gd6C2I12)2 and Cs(Gd6C2I12). Gd6C2I11 and Cs(Gd6C2I12) crystallized in the P1 space group while Gd(Gd6C2I12) and CsGd(Gd6C2I12)2 crystallized in the R3 and Pa3 space groups respectively. The magnetic susceptibility data for Cs(Gd6C2I12) indicate strong intracluster ferromagnetic coupling, but antiferromagnetic coupling suppresses the susceptibility below 150 K. DFT calculations on CsGd6C2I12 and molecular models indicate that the magnetic coupling between the basal Gd atoms is stronger than the magnetic coupling involving the axial Gd atoms in the distorted clusters.

Reproduction de : Thèse d'exercice : Médecine : Nancy 1 : 2004. / Titre provenant de l'écran-titre.