Thesis (Ph. D.)--University of Hong Kong, 1983.

No description available.

The master's thesis is dedicated to studying the propagation of ultra-high energy proton cosmic rays under a hypothesis of Lorentz invariance violation. For this purpose, numerical methods were used. Our calculations indicated that the ef- fective horizon of ultra-high energy cosmic protons is significantly extended when Lorentz invariance violation is assumed. Further, we investigated the effects of Lo- rentz invariance violation on the Cosmic ray spectrum. We learned that measured cosmic ray spectra are a suitable tool for constraining the coefficients describing Lorentz invariance violation and we estimated an interval where the upper bound on the pion Lorentz invariance violating coefficient lies. Moreover, a correlation between free parameters of the analytical model of cosmic ray spectrum and coefficients, that describes Lorentz invariance violation, was found.

The increasing frequency of sporadic weather patterns in the last decade, especially major winter storms, demands improvements in current weather forecasting techniques. Recently, there are growing interests in stratospheric forecasting because of its potential enhancements of weather forecasts. The dominating factors of northern hemisphere wintertime variation of the general circulation in the stratosphere is a phenomenon called stratospheric sudden warming (SSW) events. It is shown in multiple studies that SSW and cosmic ray muon flux variations are strongly correlated with the effective atmospheric temperature changes, which suggests that cosmic ray detectors could be potentially used as meteorological applications, especially for monitoring SSW events. A method for determining the effective temperature with cosmic ray flux measurements is studied in this work by using statistical modeling techniques, such as k-fold cross validation and partial least square regression. This method requires the measurement of the vertical profile of the atmospheric temperature, typically measured by radiosonde, for training the model. In this study, cosmic ray flux measured in Atlanta and Yakutsk are chosen for demonstrating this novel technique. The results of this study show the possibility of realtime monitoring on effective temperature by simultaneous measurement of cosmic ray muon and neutron flux. This technique can also be used for studying the historical SSW events using the past world wide cosmic ray data.

Bibliography : leaves i-xx / xi, 168, [99], xx leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1991

<p>The main aims of this project were to contribute to the knowledge about tropical climate variations, and to investigate the possibilities of obtaining cosmic ray influx data from stalagmites.</p><p>Stalagmites from Tanzania and northern South Africa were palaeoclimatologically analysed.</p><p>U-series dating, combined with previously published 14C-data (Goslar et al. 2000), shows that one of the Tanzanian stalagmites was precipitated during the latter half of the latest glacial, between approximately 39 and 27 ka. Results from stable isotope analysis (δ13C and δ18O) were interpreted as indicating millennial-scale fluctuations in atmospheric CO2-level during that time. These fluctuations show a pattern which is similar to that of the δ18O records from the GRIP and Byrd ice-cores – suggesting that the stalagmite record captures a global climate signal.</p><p>U-series dating shows that the largest of the South African stalagmites covers most of the last 25 ka. The δ13C- and δ18O-data indicate millennial-scale variation in the South African climate throughout the time of the formation of this stalagmite. Because of similarities to Antarctic records (Steig et al. 2000), the driving force for these variations was suggested to be atmospheric circulation changes associated with change in the Southern Hemisphere circumpolar westerly wind vortex. Like the Tanzanian results, these South African data lend further support to the theory about global persistent millennial-scale climate-fluctuations.</p><p>A beryllium isotope study was then performed on the two stalagmites described above. This study assesses, for the first time, the potential of the cosmogenic isotope 10Be as a tool in stalagmite studies. As a control, 9Be-analysis was also made on each 10Be-sample.</p><p>The aim of the study was to test the idea that stalagmites could be a new source of well-dated and directly climate-proxy synchronized information about past variations in cosmic ray influx intensity – i.e., a source that would serve as a new tool for general improvement of the knowledge about past variations in cosmic ray influx, and that could possibly also provide further clues to whether such variations can affect Earth’s climate.</p><p>The main excursions/fluctuations in the 10Be-and 9Be-data from these stalagmites do not coincide. Hence, the excursions in 10Be-content may be interpreted as indicating excursions in cosmic ray influx. The 10Be-data show three pronounced peaks at around 38, 35 and 21 ka respectively; plausibly corresponding to the peaks previously observed at approximately 39, 32 and 23 ka in cosmogenic isotope data from sediments and ice.</p><p>In glacial parts of the stalagmite material, the 9Be-concentration fluctuates on a millennial-scale; inversely synchronized with fluctuations in δ13C-data from the same material. This indicates that 9Be could, apart from being a necessary control for 10Be-results, also function as a palaeoclimatological proxy in stalagmite studies.</p><p>In order to improve dating facilities for stalagmites, a procedure for high-precision measurements of U and Th isotope ratios was also developed, using an IsoProbe® Multi Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICPMS). The 230Th/232Th ratio for the thorium concentration-standard Alfa Th was determined to 7.96 (±0.012) × 10-7 (2σ), and the δ234U obtained for the uranium standard SRM950a was 18.4 ±0.6(2σ). The thorium results show, that even extremely biased isotope ratios, in low-concentration samples, can be measured with remarkably good precision. The quality of each sample measurement can also easily be evaluated. However, due to repeated technical problems with the instrument, it has not yet been possible to use the developed procedure for routine analysis and dating of samples.</p>

The main aims of this project were to contribute to the knowledge about tropical climate variations, and to investigate the possibilities of obtaining cosmic ray influx data from stalagmites. Stalagmites from Tanzania and northern South Africa were palaeoclimatologically analysed. U-series dating, combined with previously published 14C-data (Goslar et al. 2000), shows that one of the Tanzanian stalagmites was precipitated during the latter half of the latest glacial, between approximately 39 and 27 ka. Results from stable isotope analysis (δ13C and δ18O) were interpreted as indicating millennial-scale fluctuations in atmospheric CO2-level during that time. These fluctuations show a pattern which is similar to that of the δ18O records from the GRIP and Byrd ice-cores – suggesting that the stalagmite record captures a global climate signal. U-series dating shows that the largest of the South African stalagmites covers most of the last 25 ka. The δ13C- and δ18O-data indicate millennial-scale variation in the South African climate throughout the time of the formation of this stalagmite. Because of similarities to Antarctic records (Steig et al. 2000), the driving force for these variations was suggested to be atmospheric circulation changes associated with change in the Southern Hemisphere circumpolar westerly wind vortex. Like the Tanzanian results, these South African data lend further support to the theory about global persistent millennial-scale climate-fluctuations. A beryllium isotope study was then performed on the two stalagmites described above. This study assesses, for the first time, the potential of the cosmogenic isotope 10Be as a tool in stalagmite studies. As a control, 9Be-analysis was also made on each 10Be-sample. The aim of the study was to test the idea that stalagmites could be a new source of well-dated and directly climate-proxy synchronized information about past variations in cosmic ray influx intensity – i.e., a source that would serve as a new tool for general improvement of the knowledge about past variations in cosmic ray influx, and that could possibly also provide further clues to whether such variations can affect Earth’s climate. The main excursions/fluctuations in the 10Be-and 9Be-data from these stalagmites do not coincide. Hence, the excursions in 10Be-content may be interpreted as indicating excursions in cosmic ray influx. The 10Be-data show three pronounced peaks at around 38, 35 and 21 ka respectively; plausibly corresponding to the peaks previously observed at approximately 39, 32 and 23 ka in cosmogenic isotope data from sediments and ice. In glacial parts of the stalagmite material, the 9Be-concentration fluctuates on a millennial-scale; inversely synchronized with fluctuations in δ13C-data from the same material. This indicates that 9Be could, apart from being a necessary control for 10Be-results, also function as a palaeoclimatological proxy in stalagmite studies. In order to improve dating facilities for stalagmites, a procedure for high-precision measurements of U and Th isotope ratios was also developed, using an IsoProbe® Multi Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICPMS). The 230Th/232Th ratio for the thorium concentration-standard Alfa Th was determined to 7.96 (±0.012) × 10-7 (2σ), and the δ234U obtained for the uranium standard SRM950a was 18.4 ±0.6(2σ). The thorium results show, that even extremely biased isotope ratios, in low-concentration samples, can be measured with remarkably good precision. The quality of each sample measurement can also easily be evaluated. However, due to repeated technical problems with the instrument, it has not yet been possible to use the developed procedure for routine analysis and dating of samples.

No description available.

A two-scintillator paddle muon telescope with variable angular acceptance at the earth's surface was used to study correlations between flux distribution and barometric pressure. The detector was placed in 2 different locations around Georgia State University with varying paddle separations of 0, 7, and 14 inches. Correlation and anti-correlation analyses were conducted by using the muon count from the detector along with the barometric pressure, surface temperature, stratospheric temperature and solar activity. It was observed that there was a short and long-term variation relationship between cosmic ray counts and barometric pressure and also cosmic ray counts and temperature. No significant relationship was found between cosmic ray flux and solar activity. A new two-scintillator paddle telescope with larger detecting area was constructed in order to observe a stronger correlation between cosmic ray flux and pressure.

The purpose of this study was to determine how well the Monte Carlo transport code FLUKA can simulate a tissue-equivalent proportional counter (TEPC) and produce the expected delta ray events when exposed to high energy heavy ions (HZE) like in the galactic cosmic ray (GCR) environment. Accurate transport codes are desirable because of the high cost of beam time, the inability to measure the mixed field GCR on the ground and the flexibility they offer in the engineering and design process. A spherical TEPC simulating a 1 um site size was constructed in FLUKA and its response was compared to experimental data for an 56Fe beam at 360 MeV/nucleon. The response of several narrow beams at different impact parameters were used to explain the features of the response of the same detector exposed to a uniform field of radiation. Additionally, an investigation was made into the effect of the wall thickness on the response of the TEPC and the range of delta rays in the tissue-equivalent (TE) wall material. A full impact parameter test (from IP = 0 to IP = detector radius) was performed to show that FLUKA produces the expected wall effect. That is, energy deposition in the gas volume can occur even when the primary beam does not pass through the gas volume. A final comparison to experimental data was made for the simulated TEPC exposed to various broad beams in the energy range of 200 - 1000 MeV/nucleon. FLUKA overestimated energy deposition in the gas volume in all cases. The FLUKA results differed from the experimental data by an average of 25.2 % for yF and 12.4 % for yD. It is suggested that this difference can be reduced by adjusting the FLUKA default ionization potential and density correction factors.