Typescript. / Digitized by Kansas Correctional Industries

Photocopy of typescript. / Digitized by Kansas Correctional Industries

This study examines variability in the isotopic composition of precipitation in southern Illinois, USA using a 5-year, event-based record, novel in its duration and in potential to extract important isotopic information of precipitation in a dynamic region, and the seasonality of major moisture sources. The isotopic composition of precipitation exhibited seasonal variations in δ18O and δ2H, where values are distinctively higher (lower) during summer (winter). Average values for d-excess were the highest (lowest) during autumn (summer). Seasonality is also present in events originating from the Gulf of Mexico (GOM), isolated by Langrangian methods. GOM JJA events showed more isotopically depleted precipitation than of non-GOM events due to a stronger “amount effect” signal (R2 = -0.40). To date, the amount effect has never been reported this far inland in the US. Precipitation analysis as it related to the ENSO phases exhibited statically significant differences in d-excess values. Precipitation events that occurred during a La Niña phase exhibited positive d¬-excess values, with an average value of 25.18‰. δ18O and δ2H values during El Niño phase were on average more depleted. Overall results highlight that the GOM, as a dominating moisture source, and ENSO phases can modulate the seasonal and intra-seasonal variability in the isotopic composition of precipitation in this region. The data collected, from a single location, can highlight moisture dynamics occurring on a regional scale and highlight the importance of the GOM as prevailing source of moisture for the Midwestern US. The second part of this study involved determining what were the best predictors for 18O and d-excess values. The study revealed that sea surface temperature and oxygen isotope values in the ambient vapor were the best predictors for 18O values but were the poorest predictors of d-excess values. The best predictors of d-excess were land surface characteristics such as the volumetric soil moisture, evaporation from bare soil variable, as well as SST, temperature of the air and specific humidity of the air. However, these predictors worked best with positive d-excess values that equaled or above 20‰.

New pedologic, carbon isotope and phytolith analyses along with stratigraphic correlations to nearby archaeological sites record the spatial and temporal distribution of past vegetation patterns in the Sac Valley Archaeological District of southwest Missouri. Radiocarbon ages obtained from a soil core along Bear Creek, CB5, are related to those from Hajic et al. (1998, 2000) indicating that the CB5 location contains correlative middle Rodgers Shelter submember deposits. This relationship also indicates that sedimentation was approximately two times greater at the CB5 locality than at the Big Eddy (23CE426) archaeological site providing much higher temporal resolution for the alluvial history as well as the vegetation proxies during the early to middle Holocene. Most midcontinent climate proxy records include indications of an early Holocene warm period when prairie replaced forests, then a cooler period in which trees dominated the landscape, followed by a warmer middle Holocene period when prairie vegetation was dominant. However, the CB5 δ13C profile of mixed C3/C4 vegetation indicates either that the vegetation at this location was not as sensitive to climate change or that this location was buffered from other influences, e.g. fires, which were critical to the expansion of prairie vegetation. On the other hand, the phytolith assemblages at CB5 indicate that there were periods with abundant C4 grasses even though the δ13C values indicate a dominance of C3 vegetation. This indicates that in the mixed forest/prairie ecotone interpretations of past vegetation from either carbon isotopes or phytolith assemblages alone may not accurately reflect patterns of vegetation. A new core, DDY-KR2, was obtained from the Big Eddy (23CE426) archaeological site and a finer resolution of δ13C values at Big Eddy increased the detail about alluvial activity and revealed subtle changes in the vegetation. The vegetation types suggested by the δ13C values for DDY-KR2 are reflected in the phytolith assemblages validating their usefulness in reconstructing local vegetation history.

The stable isotopic composition of groundwater within a watershed in eastern Iowa was studied in order to understand how water moves through the system. Samples were gathered using multiple observation wells and pore water samplers and then analyzed to determine the δ18O and δ2H of each sample. Shallow pore water is much more variable in its isotopic composition than deeper water and seems to be more greatly affected by evapotranspiration, whereas groundwater below the water table appears to show a stable isotopic signature suggesting the integration of multiple rain events. Other samples of similar depths across the slope of a hill were also used to observe differences across the area. By observing changes over time in the signatures of these samples, it can be seen that the crest of the hill is most greatly influenced by infiltration from precipitation while the side of the hill is influenced more by throughflow. By combining stable isotope analyses, knowledge of the medium through which the water is moving and the general mechanics of a watershed, a more advanced understanding of how water interacts with and moves through the ground can be gained.

The reliability of foraminifera as stratigraphic index fossils, and as isotopic proxies of marine environments, is based on the assumption that the fossil concepts represent uniform species, responding consistently to their ambient environments. Understanding sources of uncertainty is, therefore, critical. In this dissertation, I explore a potential bias in the application of planktonic foraminifera utilized extensively for Cenozoic paleo-reconstruction and, to a lesser extent, biostratigraphy: the Globigerinoides ruber-elongatus plexus (‘plexus’ meaning a complex network of interconnected members). Taxonomic revisions since 1826 have resulted in the merging of multiple Globigerinoides species names under one general designation (“Globigerinoides ruber”), the implications of which are now under scrutiny. These “morphotypes” of G. ruber have been shown to incorporate stable isotopes and trace elements in seawater dissimilarly, and correspond to multiple genetic species, some of which occupy different environments. Various criteria exist to sub-divide, group, or distinguish members of the Globigerinoides plexus, most notably the recurring use of Globigerinoides elongatus as a less spherical, less symmetrical counterpart to G. ruber. But the efficacy of these various taxonomic criteria has not been tested quantitatively. Most rely on the traits of visually distinctive “end-members,” while specimens in the morphological “transitional zone” are left to an observer’s subjective interpretation. This prevents quantification in census counts, and may lead to erroneous geochemical analyses. Furthermore, molecular clock estimates suggest that the G. elongatus species evolved significantly later than G. ruber, affecting its potential as a biomarker. In this dissertation, I examine the potential of a minimal-criteria system for classifying Globigerinoides-type morphologies using only three conditions: final chamber compression, final chamber asymmetry, and aperture compression. Morphometric analyses on specimens grouped according to this new system allow us to assess to what degree visual classification reflects morphospace discontinuity. Armed with this information, I then explore potential isotopic offsets between members of the Globigerinoides plexus, and its use in reconstructing regional differences in climate or habitat influences in the Gulf of Mexico and Caribbean basins. Finally, having shown that G. ruber and G. elongatus can be reliably visually distinguished, I tracked the species’ fossil presence individually in a deep core from the South China Sea, and confirmed the presence of G. ruber in the South China Sea through the late Miocene, and G. elongatus through the Pleistocene. While it is believed that neither species was traced to its true first occurrence (FO), the relative FO of G. ruber was shown to be 4–5 Ma before G. elongatus

No description available.

No description available.

Radium needles that were once implanted into tumours as a cancer treatment are now obsolete and constitute a radioactive waste problem, as their half-life is 1600 years. The reduction of radium by photonuclear transmutation by bombarding Ra-226 with high-energy photons from a medical linac has been investigated. The irradiated needles would then be processed to remove the Ac-225, which can then be used for .Targeted Alpha Therapy. (TAT) of cancer. This project has the potential to slowly reduce obsolete radioactive material, and displace future expensive importation of Ac-225 from Russia, Germany (Institute for Transuranium Elements - ITU) and the US in the years ahead. This thesis progresses through a number of stages and begins by providing a background to the usefulness of Ac-225 as an alpha emitter, some of the equipment used in the experimental work such as linear accelerators and detectors, as well as the initialisation of a process whereby a reliable source of high-grade radium is secured, suitable equipment obtained, followed by a series of experiments leading to the production of the desired product, actinium and bismuth. The second stage of this study involved the formulation of a theoretical model in which the bremsstrahlung photon spectrum at 18 MV linac electron energy is convoluted with the corresponding photonuclear cross sections of Ra- 226. This enabled the total integrated yield of Ra-225 and its daughter product Ac-225 to be obtained. The third stage of this study ties the theoretical and experimental work together by presenting the results of a number of experiments performed on radium sources. These experiments were performed over a period of about three years using a variety of detectors in a hospital setting. These experiments, as presented in this thesis, demonstrate that Ac-225 can be produced in small quantities by a medical linac or in commercial quantities by the use of a high-powered linac or cyclotron, thereby, ensuring a reliable supply of Ra-225 for TAT and also reducing the radium waste product. / Doctor of Philosophy

R.J. Hull and H.H. Stroke. / "November 1, 1961." "Reprinted from Journal of the Optical Society of America, vol.51, no. 11, 1203-1212, November, 1961." / Includes bibliographical references. / Army Signal Corps Contract DA36-0390-sc-78108. Dept. of the Army Task 3-99-20-001 and Project 3-99-00-000.