[Truncated abstract.] An apparatus has been built, tested and characterised with greatly increased precision and accuracy to enable spin-polarised electron impact explorations of angular momentum effects in atoms. A combination of experimental, computational and interpretative studies has revealed new phenomena. In zinc the polarisation of the radiated photons from excited and ionised-with-excited atoms was measured in terms of integrated Stokes parameters (P1, P2 and P3) and related to electron exchange and spin-orbit interaction using normalised state multipoles.

Thesis (M.S. in Physics)--Naval Postgraduate School, May 1966. / Thesis Advisor(s): Riggin, John D. "May 1966." Description based on title screen as viewed on June 2, 2010. DTIC Descriptor(s): Reactor Cores, Gases, Fission Products, Gases, Gamma Ray Spectra, Radioactive Isotopes, Krypton, Xenon. DTIC Identifier(s): AGN-201 Reactors. Author(s) subject terms: Reactor Gas, Xenon Gamma Spectrum, Krypton Gamma Spectrum. Includes bibliographical references (p. 36). Also available in print.

Univ., Diss., 2009--Kassel.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1984. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 211-215).

Coronary artery disease has become a world wide medical problem. There is an overwhelming association between coronary atherosclerosis, angina pectoris, acute myocardial infarction and sudden death. The narrowing of coronary arteries is thought to damage the heart by limiting appropriate changes in coronary blood flow and by causing myocardial ischemia. This thesis attempts to examine the coronary circulation in patients who present with chest pain with and without coronary artery disease. One of the aims of this thesis is to validate the use of a short-lived radionuclide to study changes in regional myocardial perfusion. This technique has been applied in clinical medicine in an attempt to describe the disturbances of regional myocardial perfusion that occur in patients with coronary artery disease. These disturbances of perfusion have been related to the patients' symptoms, the electrocardiogram and the stenosed arteries seen in the arteriogram. Krypton-81m in solution is an inert freely diffusible gas (half-life 13 seconds) which emits a single 190 kev gamma ray. This tracer, a special catheter and a gamma camera have been developed in experiments to measure changes in regional myocardial perfusion. The systematic and rand-Om errors of the method have been defined in experiments. The results show that the mixing and delivered arterial concentration of krypton-81m are stable within a useful physiological range of changes in heart rate, blood pressure and coronary blood flow. Correlations with a reference technique have shown that the method can measure changes in regional myocardial perfusion between O and 3 ml/ml/min. The invasive method, the planar imaging and the need for calibration with washout at high levels of perfusion are investigated and described as limitations that must be considered. Eighty patients presenting with chest pain have been investigated by routine clinical methods, precordial mapping of the electrocardiogram during exercise and coronary arteriography. Changes in regional myocardial perfusion at rest and during atrial pacing has been measured using krypton-81m. The results have shown that stable mixing and delivered arterial concentration of krypton-81m can be achieved in the patients. Fifteen patients with negative exercise tests all demonstrated uniform increases in regional myocardial perfusion with pacing. The remaining 65 patients with positive exercise tests and significant coronary artery disease all showed both regional increases and decreases in myocardial perfusion during atrial pacing. In 16 of the 65 patients the jeopardized segment of ventricular myocardium showed significant increases in perfusion during the first 4 to 7 minutes of pacing. Th e increase stopped and regional perfusion in the affected segment then decreased progressively until the pacing was stopped. In 23 of the 65 patients the affected segment showed no changes in perfusion for 5 to 7 minutes of atrial pacing and then showed progressive decreases in regional myocardial perfusion until the pacing was stopped. Finally, in 26 of the 65 patients the affected segment showed immediate and progressive decreases of regional myocardial perfusion starting with the commencement of atrial pacing. In all the patients with disturbed perfusion ST segment depression in the electrocardiogram appeared after (140 ± 14 sec) the regional decrease of myocardial perfusion in the affected segment. Chest pain always appeared later at 220 ± 19 sec after the appearance of disturbed myocardial perfusion. Regional myocardial perfusion returned to normal in all the patients after the atrial pacing was stopped. There was a spatial relationship between the region of the ventricles affected by disturbed perfusion and the region of the precordium showing abnormal electrocardiographic signs during the exercise test. In conclusion, this clinical study has shown that patients with chest pain who have coronary artery disease suffer decreases of regional myocardial perfusion in affected segments of the ventricles during episodes of angina pectoris induced by atrial pacing. Regional perfusion may increase, remain stable or decrease in the affected segment following the onset of a stress test such as atrial pacing. This probably represents the amount of reserve function and adaptation left in the diseased coronary circulation and may be a useful physiological indicator of the severity of coronary disease and of patients at high risk. ST segment depression and pain have a close temporal relationship to the decreases of regional myocardial perfusion that occur in these patients. These studies suggest that there is a close relationship between myocardial perfusion and metabolism in health and disease. Both myocardial perfusion and metabolism will have to be affected by any rational therapy for angina pectoris and ischemic heart disease.

The physisorption of Kr on graphitic amorphous carbon (g-C) has been investigated using a statistical approach. The interaction energy calculation process (i) established a structural model of g-C and (ii) determined the adsorbate-adsorbate and the adsorbate-substrate interaction potentials on g-C. The structural model of g-C was divided into three regions. For the interaction potential between a Kr atom and a carbon atom the short and medium range order of g-C was described with a discrete medium model based on three ring clusters using ring statistics from Beeman's continuous random network C1120 model of g-C. For the intermediate distance region, Beeman's radial distribution function was used to model g-C. A homogenous and isotropic continuous medium model was used at large distances. The Kr-Kr and Kr-g-C interaction potentials used for Kr on g-C, which are pair-wise Lennard-Jones 6-12 potentials, are similar to Kr on graphite potentials. the validity of the model for g-C and the potentials were verified though calculations for Kr on graphite. Results compared favorably with recent literature values. The interaction energy calculation results for Kr on a g-C substrate assert that (i) Kr adlayers will form on g-C, (ii) the structure of the Kr adlayer is governed by the substrate corrugation at low coverage and by the Kr-Kr interaction at high coverage, and (iii) there is no direct relation between the structure of Kr adlayers on g-C and those on graphite. The average binding energy of Kr on g-C is comparable with that on graphite, but the corrugation of g-C is perhaps six times that of a graphite substrate. The wrinkling of the g-C surface, due to the presence of a distribution of 5-, 6-, and 7- membered rings, is responsible for this large corrugation of the g-C substrate.

No description available.

The yields of xenon and krypton from the neutron- induced fission of Am241 and Am242 have been measured with a mass spectrometer. This was accomplished by irradiating samples of Am241 for different lengths of time so that the effect of the growth of highly fissionable Am242 could be determined. These studies reveal that both the degree of fine structure in the mass yield curve and the fission-product charge distribution are dependent on the energy of the incident neutrons. This has not been previously observed for any fissioning nuclide. These studies also reveal effects of the 50-neutron shell and of the neutron-proton ratio of the fissioning nuclide on the mass yield curve. / Thesis / Doctor of Philosophy (PhD)

The goal of this research was to identify and fabricate zeolitic membranes that can separate radioisotope krypton-85 (half-life 10.72 years) and xenon gas released during spent nuclear fuel reprocessing. In spent nuclear fuel reprocessing, fissionable plutonium and uranium are recovered from spent nuclear fuel and recycled. During the process, krypton-85 and xenon are released from the spent nuclear fuel as process off-gas. The off-gas also contains NO, NO2, 129I, 85Kr, 14CO2, tritium (as 3H2O), and air and is usually vented to the atmosphere as waste without removing many of the radioactive components, such as 85Kr. Currently, the US does not reprocess spent nuclear fuel. However, as a member of the International Framework for Nuclear Energy Cooperation (IFNEC, formerly the Global Nuclear Energy Partnership), the United States has partnered with the international nuclear community to develop a “closed” nuclear fuel cycle that efficiently recycles all used nuclear fuel and safely disposes all radioactive waste byproducts. This research supports this initiative through the development of zeolitic membranes that can separate 85Kr from nuclear reprocessing off-gas for capture and long-term storage as nuclear waste. The implementation of an 85Kr/Xe separation step in the nuclear fuel cycle yields two main advantages. The primary advantage is reducing the volume of 85Kr contaminated gas that must be stored as radioactive waste. A secondary advantage is possible revenue generated from the sale of purified Xe. This research proposed to use a zeolitic membrane-based separation because of their molecular sieving properties, resistance to radiation degradation, and lower energy requirements compared to distillation-based separations. Currently, the only commercial process used to separate Kr and Xe is cryogenic distillation. However, cryogenic distillation is very energy intensive because the boiling points of Kr and Xe are -153 °C and -108 °C, respectively. The 85Kr/Xe separation step was envisioned to run as a continuous cross-flow filtration process (at room temperature using a transmembrane pressure of about 1 bar) with a zeolite membrane separating krypton-85 into the filtrate stream and concentrating xenon into the retentate stream. To measure process feasibility, zeolite membranes were synthesized on porous α-alumina support discs and permeation tested in dead-end filtration mode to measure single-gas permeance and selectivity of CO2, CH4, N2, H2, He, Ar, Xe, Kr, and SF6. Since the kinetic diameter of krypton is 3.6 Å and xenon is 3.96 Å, zeolites SAPO-34 (pore size 3.8 Å) and DDR (pore size 3.6 Å) were studied because their pore sizes are between or equal to the kinetic diameters of krypton and xenon; therefore, Kr and Xe could be separated by size-exclusion. Also, zeolite MFI (average pore size 5.5 Å) permeance and selectivity were evaluated to produce a baseline for comparison, and amorphous carbon membranes (pore size < 5 Å) were evaluated for Kr/Xe separation as well. After permeation testing, MFI, DDR, and amorphous carbon membranes did not separate Kr and Xe with high selectivity and high Kr permeance. However, SAPO-34 zeolite membranes were able to separate Kr and Xe with an average Kr/Xe ideal selectivity of 11.8 and an average Kr permeance of 19.4 GPU at ambient temperature and a 1 atm feed pressure. Also, an analysis of the SAPO-34 membrane defect permeance determined that the average Kr/Xe selectivity decreased by 53% at room temperature due to unselective defect permeance by Knudsen diffusion. However, sealing the membrane defects with polydimethylsiloxane increased Kr/Xe selectivity by 32.8% to 16.2 and retained a high Kr membrane permeance of 10.2 GPU at ambient temperature. Overall, this research has shown that high quality SAPO-34 membranes can be consistently fabricated to achieve a Kr/Xe ideal selectivity >10 and Kr permeance >10 GPU at ambient temperature and 1 atm feed pressure. Furthermore, a scale-up analysis based on the experimental results determined that a cross-flow SAPO-34 membrane with a Kr/Xe selectivity of 11.8 and an area of 4.2 m2 would recover 99.5% of the Kr from a 1 L/min feed stream containing 0.09% Kr and 0.91% Xe at ambient temperature and 1 atm feed pressure. Also, the membrane would produce a retentate stream containing 99.9% Xe. Based on the SAPO-34 membrane analysis results, further research is warranted to develop SAPO-34 membranes for separating 85Kr and Xe.

Thesis (Ph. D. in Physics)--Vanderbilt University, Dec. 2005. / Title from title screen. Includes bibliographical references.