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Rate of long term bleaching in FK 51 optical glass darkened by Co60 ionizing radiation at dose rates of 10 krad/hr and 7 rad/hr

Description: A previous paper presented long term bleaching data on various glasses exposed to 10.6 krad of ionizing radiation. All the glasses reported except FK 51 have readily available `G` glass equivalents that are stabilized to the natural space environment. Yet, FK 51, because of its location on the Abbe diagram is extremely useful in certain lens design applications. To more fully explore the bleaching of FK 51, after the initial dose of 10.6 krad at 11.8 krad/hour, we irradiated three more samples at a similar dose rate but to different total doses. Since the dose rate for this study was significantly higher than the dose rate anticipated for glasses in as shielded space-based lens system (tilde 3 rad/day), additional data were obtained at a lower rate of 7 rad/hour. While this dose rate is still higher than the anticipated operational rate, it is more than 1000 times lower than the dose 011 011 011 rate used for our initial studies. The bleaching rate for the samples exposed at the lower dose rate is considerably less than for the samples exposed at the higher rate.
Date: July 1997
Creator: Wirtenson, G. R. & White, R. H.
Partner: UNT Libraries Government Documents Department

Effects of gamma-ray irradiation on M1 propellant

Description: Samples of M1 single-base propellant were exposed to 10{sup 5}, 10{sup 6}, and 10{sup 7}r of Co{sup 60} gamma rays. Burning rates were determined over a pressure range of 600 to 2600 psi at -40{degrees}, 21{degrees}, and 71{degrees}C. A statistical study indicated no significant change in the burning rate and a small but statistically significant increase (6%) in the exponential factor n after the 10{sup 7}r dose. Visible deterioration resulted, as the color changed from yellow to dark brown and the surface became uneven. In view of these marked visible effects, the slight change in burning rate is surprising. One sample exposed to 5 {times} 10{sup 8}r showed severe blistering, swelling, and contraction, and embrittlement causing fracture. Nitrogen Taliani tests conducted at 110{degrees}C indicated that the decomposition rate is decreased by exposure to 10{sup 5}r, is decreased less by 10{sup 6}r, and remains unchanged after 10{sup 7}r exposure. Chemical analysis showed that the percentage of 2-nitrodiphenylamine increases with dose by a factor of 7 at 10{sup 7}r, while, at the same time, the nitrogen content of the nitrocellulose decreases with increasing dose. This indicates that a substantial part of the nitrocellulose decomposition product had reacted with the diphenylamine stabilizer. It is remarkable that propellant strands obviously modified by exposure to 10{sup 7}r showed little or no change in burning rate.
Date: April 1, 1964
Creator: Abel, J.E.; Mapes, J.E. & Levy, P.W.
Partner: UNT Libraries Government Documents Department

LET dependence of DNA-protein cross-links

Description: We have preliminary data indicating a fluence-dependent yield of particle-induced protein cross-links (DPC`s) with a dependency on LET and particle residual energy. Our data indicate that the DPC yield for hamster fibroblasts in vitro irradiated at 32 keV/{mu}m is similar to that reported for hamster cells irradiated with cobalt-60 gamma rays. At 100-120 keV/{mu}m there is some evidence for an enhanced DPC yield with increasing particle fluence, but there are differences in the yields that are dependent on particle track structure.
Date: August 1, 1995
Creator: Blakely, E.A.; Chang, P.Y. & Bjornstad, K.A.
Partner: UNT Libraries Government Documents Department

Physical principles of ion-beam processing of polymeric materials and applications

Description: Irradiation of polymeric materials with energetic ions in the range of several hundreds of keV to several MeV causes drastic changes in physical, chemical, and mechanical properties. Studies indicate that irradiation produces many active radicals which then react with each other, transforming spaghetti-like tangled polymer chains into a highly cross-linked network structure. Analysis of experimental data shows that the most important parameter for cross-linking is the deposited energy density along the ion track, often expressed in terms of linear energy transfer (LET) in units of eV/nm. High LET produces a high number of free radicals over many neighboring molecular chains and thereby facilitates cross-linking. On the other hand, under low LET conditions, radicals are produced so sparsely that cross-linking efficiency decreases. Moreover, the deposited energy in the chain often leads to chain scission when there are no radicals in the neighboring chains for crosslinking. This paper reviews the current understanding of cross-linking mechanisms in terms of nuclear and electronic stopping and their impact on materials` properties.
Date: November 1, 1998
Creator: Lee, E.H.
Partner: UNT Libraries Government Documents Department

Chemistry induced by the selective excitation of core electrons in biomolecules. Final project report, April 1, 1993--April 30, 1996

Description: The key feature of this research is the use of tunable monochromatic x-rays from synchrotron sources to investigate the effects of ionizing radiation on uracil and prolinamide. These sources provide the new capability of enhancing significantly the selective ionization or excitation of a specific atom in a molecule by tuning the photon energy to the core-ionization threshold for that atom or by tuning to a neutral core-hole resonance associated with that atom. As a result, chemical transformations caused directly by the core-electron ionization or excitation can be separated from those caused by secondary excitation steps. The chemistry associated with the secondary excitations also can be examined more precisely than has been done in the past because the energy of the emitted photoelectrons and Auger electrons can be controlled and varied, and direct ionization of the solvent or matrix also can be controlled, i.e. reduced or enhanced selectively by varying the x-ray energy and selecting matrix materials with small or large x-ray absorption cross sections. Experiments are performed by isolating target molecules in thin solid films.
Date: August 1, 1997
Creator: Hanson, D.M.
Partner: UNT Libraries Government Documents Department

Radiation chemical effects of X-rays on liquids

Description: This review describes some of the chemical changes induced by photoelectrons which are released in liquids when X-rays are absorbed. Both experimental studies and theory are discussed. In part 1, the basic processes occurring upon absorption of X-rays are described. Parts 2 and 3 deal with hydrocarbon liquids; in part 2 the ion yields, including effects at K-edges, and in part 3, the yields of excited states. Part 4 discusses chemical effects of X-rays in aqueous solutions. The authors end with a summary of future needs and directions.
Date: November 1, 1998
Creator: Holroyd, R.A. & Preses, J.M.
Partner: UNT Libraries Government Documents Department

The partitioning of uranium and neptunium onto hydrothermally altered concrete

Description: Cementitious materials that are used to construct the ground support for high-level repositories have a high probability of interacting with radionuclide-bearing fluids derived from failed waste packages. Cementitious materials provide a highly alkaline environment; pore fluids in concrete can have pH {gt} 10 for thousands to hundreds of thousands of years. Studies have shown that fresh concrete and cement phases strongly retard or immobilize certain actinides. Consequently, cementitious materials may serve as a barrier to the release of the radionuclides to the far field. However, the effect of thermal alteration of these materials, which may occur in high-level repositories, on their interaction with radionuclides has not been addressed. In contrast to retardation, colloidal silica-enriched particles that are abundant in the pore fluids of cementitious materials may facilitate radionuclide migration through the near-field into the adjacent geological environment. Due to the uncertainties of these two opposite effects, it is important to investigate the interaction of actinides with cementitious materials under varying conditions. It is expected that cementitious materials in high-level waste repositories will be subjected to and altered by hot dry and/or humid conditions forhundreds to thousands of years by the time they interact with radionuclide-bearing fluids. After alteration, the chemical and mineralogical properties of these materials will be significantly different from that of the as-placed or fresh concrete. To assess the effect that this alteration would have on radionuclide interactions, samples of hardened concrete (untreated concrete) were hydrothermally heated at 200 C for 8 months (treated concrete). The concrete used in the experiments consisted of portland cement with an aggregate of dolomitic limestone. X-ray diffraction analysis has shown that portlandite and amorphous calcium silicate hydrate gels were converted to the crystalline calcium silicate hydrate minerals tobermorite, xonotlite, and scawtite, and clay minerals by the hydrothermal treatment. Calcite, dolomite, and quartz ...
Date: October 14, 1999
Creator: Zhao, P.; Allen, P.G.; Sylwester, E.R. & Viani, B.E.
Partner: UNT Libraries Government Documents Department

Analysis of Hydroperoxides in solid Polyethylene by NMR and EPR Spectroscopy

Description: The authors have shown that the hydroperoxide species in {gamma}-irradiated {sup 13}C-polyethylene can be directly observed by {sup 13}C MAS NMR spectroscopy. The experiment was performed without the need for special sample preparation such as chemical derivatization or dissolution. Annealing experiments were employed to study the thermal decomposition of the hydroperoxide species and to measure an activation energy of 98 kJ/mol. EPR spectroscopy suggests that residual polyenyl and alkylperoxy radicals are predominantly trapped in interracial or crystalline regions, while the peroxy radicals observed after UV-photolysis of hydroperoxides are in amorphous regions.
Date: June 12, 2000
Partner: UNT Libraries Government Documents Department

Empirical potentials for recombination reactions of photo-dissociated ligands. Final report

Description: The aim of this research was to design an appropriate potential and simulation methodology to describe the effect of radiation on ligands bound to metal-proteins. As model systems the authors investigated myoglobin, hemoglobin and their mutants. The great advantage of the globins as a target for theoretical studies is the wealth of experimental data available for them. They focused on studies that combine fast spectroscopy with mutation experiments. The mutations make it possible to examine detailed changes in the kinetic curves with atomically detailed information. The first spectroscopy, which is in the same time scale as of ordinary molecular dynamics (sub nanoseconds), makes it possible to compare the results of the computations to raw experimental data.
Date: December 1, 1998
Creator: Elber, R.
Partner: UNT Libraries Government Documents Department

Spin probes of chemistry in zeolites

Description: Electron spin resonance (EPR) studies in zeolites are reviewed in which radiolysis was used to ionize the zeolite lattice, create reactive intermediates, spin label reaction products and to provide a window onto chemistry and transport of adsorbates and matrix control of chemistry. The review examines reactions of radical cations and the influence of the geometry constraints inside the zeolite, explores how zeolite model systems can be used to learn about energy and charge transfer in solids and illustrates the use of radiolysis and EPR for in situ spectroscopic studies of solid-acid catalysis. The various spin probes created inside the zeolite pores report on properties of the zeolites as well as shed light on radiolytic processes.
Date: September 1, 1997
Creator: Werst, D.W. & Trifunac, A.D.
Partner: UNT Libraries Government Documents Department

Effect of radiation on proteins and radiation effects in biochemistry and organic chemistry. Final report, October 15, 1957--October 14, 1974

Description: A summary is made of a fifteen year study of chemical effects of radiation of amino acids and proteins. Included is a list of publications: 54 papers, reports and abstracts, and 10 M.S. and Ph.D theses. The report concludes with details of the final two studies done under this contract. These are, first, a study of post-irradiation effects of various gases on gamma irradiated lysozyme. This study showed that H$sub 2$S, O$sub 2$, NO, and N$sub 2$O treatment changed the amount of aggregation products, and also that a certain amount of the irradiated lysozyme was subject to main chain cleavage. The second was a study of proteins in rabbit eye lens cataracts induced by x-irradiation or a high galactose diet. The cataract proteins were more soluble in water than normal proteins, and were present in lower amounts in the eye lens. (auth)
Date: January 1, 1974
Creator: Tolbert, B.M.
Partner: UNT Libraries Government Documents Department

Observations on the Radiation Decomposition of Some C14 LabeledCompounds

Description: Varying amounts of radiation decomposition during storage in the dry form have been found in the cases of C{sup 14}-labeled valine, norvaline, norleucine, choline chloride, calcium glycolate and cholesterol. These data indicate that investigators using labeled organic compounds should make frequent checks of the purity of these compounds in order to exclude the possibility of the presence of decomposition products.
Date: February 27, 1953
Creator: Tolbert, B.M.; Adams, P.T.; Bennett, Edward L.; Hughes, Ann M.; Kirk, Martha R.; Lemmon, R.M. et al.
Partner: UNT Libraries Government Documents Department

Fracture energy and strength of polymer impregnated cement

Description: The fracture energy, or effective surface energy of hardened cement paste and polymer-impregnated hardened cement paste, was measured by an analytical method. The fracture energy of polymer impregnated hardened cement paste is considerably higher than the unimpregnated paste (7.5 x 10/sup 4/ to 0.91 x 10/sup 4/ ergs/ cm/sup 2/). The increase appears to be entirely due to the polymer contribution. The results predict a factor of 5 improvement in the fracture strength of hardened cement paste upon polymer impregnation. (auth)
Date: February 1, 1974
Creator: Auskern, A. & Horn, W.
Partner: UNT Libraries Government Documents Department