Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1981. / Supervised by Michael P. Bacon. Vita. Includes bibliographical references (leaves 262-273).

The work described in this thesis concerns the synthesis of actinide complexes and their reactivity towards small unsaturated molecules. Complexes bearing tetraphenoxide, borohydride and boroxide ligands have been evaluated. Additionally, work towards the synthesis of heterobimetallic uranium transition metal complexes and their applications in catalysis is discussed. Chapter one reviews important organoactinide complexes reported in the literature which effect chemical transformations on small unsaturated substrates. Actinide complexes supported by aryloxide or borohydride ligands are reviewed, along with actinide complexes in which metal p-arene interactions are present. Chapter two reports the synthesis and characterisation of a set of tetraphenol ligands, in addition to a number of attempted synthetic routes to tetraphenol ligands with alternate substitution. The chemistry of those tetradentate aryloxide ligands is introduced with bimetallic uranium(IV) and thorium(IV) complexes using different An(IV) and U(III) precursors. Chapter three reports the synthesis and characterisation of monometallic uranium and thorium complexes using a tetraphenol ligand. The varying chemistry between the two similar An(IV) ions, where the uranium complexes exist as a mixture of oligomers and the thorium complexes remain as well defined mononuclear complexes, is discussed within. A range of base adducts of mononuclear actinide complexes are reported, including a thorium trimethylsilylazide complex, a rare example of a metal organoazide. Chapter four describes the synthesis of homoleptic boroxide and heteroleptic borohydride complexes of uranium(III). The reactivities of these complexes with small unsaturated molecules are assessed, including the reaction of a low coordinate uranium(III) boroxide complex towards CO2 to provide a dinuclear uranium carbonate bridged complex. Chapter five introduces work towards heterobimetallic uranium transition metal complexes carried out in the Arnold group. The application of these complexes towards ring opening polymerisation chemistry is discussed in addition to investigations into the incorporation of transition metals into uranium(IV) complexes. Chapter Six presents the detailed experimental methods used to carry out this research.

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The M-shell x-ray production cross section for thorium and uranium have been determined for protons of energy 0.4 - 4.0 MeV, helium ions of energy 0.4 - 6.0 MeV, carbon ions of energy 4.5 - 11.3 MeV and oxygen ions of energy 4.5 - 13.5 MeV. The total cross sections and the cross sections for individual x-ray peaks in the spectrum, consisting of the following transitions Mz (M4-N2, M5-N3, M4-N3), Ma (M5-N6,7), Mb (M4-N6, M5-O3, M4- O2), and Mg (M4-O3, M5-P3, M3-N4, M3-N5), were compared to the theoretical values determined from the PWBA + OBKN and ECUSAR. The theoretical values for the carbon and oxygen ions were also modified to take into account the effects of multiple ionizations of the target atom by the heavier ions. It is shown that the results of the ECUSAR theory tend to provide better agreement with the experimental data.

The U/Th dating method has been applied to five archeological sites in France. The U/Th method relies upon the co-precipitation of uranium with calcium carbonate in speleothems formed in caves. Because 230Th forms in the calcite from the decay of 234U a radiometric clock is begun in the newly deposited calcite. Dates are derived from measuring the isotopic abundances of the uranium and thorium in the calcite. For many archeological samples, preroasting of the sample before analysis is necessary to improve the yields. Normally, relative dates for archeological sites are derived from the comparison of paleoclimatic interpretations determined from sedimentological, faunal, and palynological studies of the cave sediments with global climatic records. These methods have established that the Mousterian culture and Neanderthals appeared in Europe at the beginning of the Würm, 80 Ka BP. Absolute dates determined for samples from Lachaise, Montgaudier, Pech de l'Aze, Abri Vaufrey, and Grotte 13, where archeological or faunal material is associated stratigraphically with speleothems sampled, have established that there were several regional climatic phenomena experienced in southern France. These events are dated at 80 to 120 Ka BP, interpreted to be the Riss/ Würm interglacial, and at 38 to 50 Ka, interpreted to be the Würm I/II interstadial. Furthermore, archeological materials and human skeletal remains associated with these sites and the speleothems therein, have proven that the Nean~erthals must have evolved prior to 150 Ka BP, but that they did not develop their Mousterian culture until about 125 Ka BP. / Thesis / Master of Science (MSc)

Die Reaktivität acyclischer Carbene, N-heterocyclischer Silylene und Germylene gegenüber verschiedenen Boranen sowie die weitere Reaktivtät der erhaltenen Verbindungen wird untersucht. Im zweiten Teil wird die Darstellung und Reaktiviert einiger Thorium- und Lanthanoidhydridoboratkomplexe genauer beleuchtet. / The reactivity of acyclic carbenes, N-heterocyclic silylenes and germylenes with different boranes and the reactivity of obtained substances is studied in detail. The second part deals with the synthesis and reactivity of thorium and lanthanide hydridoborate complexes.

In the process of exploring the thorium fuel application in CANDU reactors, it is important to consider the proliferation resistance level as a parameter for comparison with current natural uranium fuel. The concept of a whole fuel cycle was introduced to show the variations in the proliferation resistance level as the material is flowing through the cycle. The depletion and decay histories were simulated with SCALE 6.1 code and the results such as isotopes composition, decay heat, and radioactivity were used to analyze the material attractiveness of pure heavy metal for weapon production. They also served as the intrinsic features during the proliferation resistance level calculation. The Multi-Attribute Utility Analysis (MAUA) method developed by Chalton was used to compare different CANDU fuel cycles with quantified values (PR) from the viewpoint of proliferation resistance. To improve the biased MAUA results that gave a PR of 0.76 to CANDU while 0.93 to PWR, the attributes of size/weight and refueling scheme were reconsidered. In addition, the sensitive technology involved was added for the proliferation resistance recalculation. The results showed an increased PR value of 0.82 for natural uranium CANDU reactor as well as a decreasing trend of PR at the back end. PWR has a PR of 0.82 with revised MAUA method. The PR comparison of thorium and natural uranium fuel indicated that Th/Pu fuel has a slightly higher PR value in the reactor. The Figure of Merit (FOM) method developed by Bathke was used to validate the PR results from another perspective: the attractiveness of pure heavy metals that are suitable for nuclear weapon production. The results showed that FOM of plutonium keeps increasing with decay time and the trend becomes more significant after disposal in the deep geological repository. The FOM of uranium from Th/Pu cases is higher than that of Pu within several hundred years but maintains a decreasing trend. The decreasing FOM of uranium is preferred for direct disposal in deep geological repository. The decreased PR level and the increased FOM value of plutonium at the back end of a fuel cycle indicate the importance of implementing the security and safeguard for each facility dealing with nuclear materials. The comparison results of PR and FOM values for different fuel provided feedback and suggestions for the new fuel application. / Thesis / Master of Applied Science (MASc)