Browsing by Author "Yennello, Sherry"

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REU Site: Nuclear Science at Texas A&M
Cyclotron Institute; TAMU; https://hdl.handle.net/20.500.14641/609; National Science Foundation
This award supports the renewal of the Research Experiences for Undergraduates (REU) site in nuclear physics at Texas A&M University. The site will support twelve undergraduates per year in ten weeks of research during the summer months. Involvement in research at the undergraduate level is an important component in increasing the numbers and preparation of students entering graduate programs. This site primarily targets students who lack opportunities to do research in the field of Nuclear Science at their home institutions. The student research projects are at the leading edge of Nuclear Science, including sub-fields such as nuclear astrophysics, weak interactions, nuclear dynamics and thermodynamics, nuclear structure, the Relativistic Heavy Ion Collider (RHIC), atomic ionizations, and radiation effects. There are proposed projects both in theoretical and experimental Nuclear Science. The Cyclotron Institute is a Department of Energy (DOE) Nuclear Physics Center of Excellence. The facilities include a K500 superconducting cyclotron, a K150 cyclotron and associated state-of the art detector systems. The Cyclotron Institute and the department of physics are also home base for involvement in experiments at other facilities, and the faculty are leading scientists in the field and have a history of working with undergraduates in their research programs.
Study of Nuclear Forces and Shell Evolution through Spectroscopy of Neutron-Rich Light Nuclei
Cyclotron Institute; TAMU; https://hdl.handle.net/20.500.14641/609; DOE-Office Of Science
Iodine-129 (129I), with a half-life of half-life of 16 million years, is commonly considered the single greatest risk driver in high-level and low-level nuclear repositories. This risk stems from several basic properties of 129I, and under many geochemical conditions, it can move as an anion at nearly the rate of water through the subsurface environment. 129I is also extremely radiologically toxic because over 90% of body burden accumulates in the thyroid, which weighs only about 14g in an adult. There is also a large worldwide inventory of radioiodine as a result of its high fission yield and this inventory is rapidly increasing as a result of nuclear energy production. Radioiodine is produced at a rate of 40 GBq (1 Ci) per gigawatt of electricity produced by nuclear power. To illustrate how the properties of 129I magnify its risk, 129I accounts for only 0.00002% of the radiation released from the Savannah River Site in Aiken, South Carolina, but contributes 13% of the population dose, a six orders of magnitude magnification of risk with respect to its radioactivity. The currently favored solid phase for LLW immobilization is cement, while HLW immobilization is the incorporation of waste into glass (vitrification). However, so far, the incorporation into cement and subsequent leaching of only iodide has been seriously investigated. The major problem with this approach is that it ignores the complex speciation of iodine, i.e., it ignores iodate and organo-iodine which have different chemistries. Most of the past research was devoted to the mechanism of iodide uptake in cement hydrate phases that is sorption and/or incorporation. Very few data exist on iodate and organo-iodine incorporation in cement, even though large quantities of liquid waste containing also radioiodine have already been solidified in cement Iodine-129 from low-level waste is commonly disposed of in cementitious materials. Grout, a dense cementitious fluid, mixed with a reducing slag, is often used to immobilize radionuclides. However, the reducing environment might not be conducive to immobilize iodine. For example, the silver based immobilization technologies (e.g., AgCl, Ag-impregnated granular activated carbon, Ag-mordenite) remove iodine from the aqueous phase by promoting the formation of Ag-iodide precipitates. The solubility of AgI is eight orders of magnitude lower than it is for AgIO3. Similarly, coprecipitation of iodine into calcium carbonate phases occurs only with IO3- and not with I- and org-I. If one would want to immobilize iodine more effectively, different engineering approaches would need to be used to promote binding of I-, IO3-, or organo-I. Using laboratory experiments with grout, slag, and silver-based adsorbents, and GC-MS and I K-edge XANES and EXAFS and C K-edge XANES spectroscopy for identifying iodine speciation, the major problems with these methods have been identified as focused too much on just one of the iodine species for immobilization, while others, especially organo-I, remained mobile. Finally, we established that most of the adsorbents that are used contain sufficient amounts of organic matter to create organo-I . It is anticipated that increased attention directed at understanding and quantifying the speciation of radioiodine, as opposed to simply total radioiodine, will lead to improved remediation results to be used for long-term radioiodine disposal in cementitious waste forms.