published_or_final_version / Physics / Master / Master of Philosophy

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Since 1950's there has been a growing interest of understanding the effects of cosmic ray radiation on the increase in average global temperature. Recent studies showed that galactic cosmic rays play a significant role in the formation of low cloud coverage and its consequent impact on the global temperature variation of the earth. A long-term measurement of the cosmic ray flux distribution at the surface of the earth has been established at Georgia State University. The current effort is focused on understanding the correlations between the cosmic ray particle flux distribution and the atmospheric and space weather measurements. In order to understand the observed atmospheric effects on cosmic ray flux, numerical simulations of cosmic muon and neutron flux variations at the surface of the earth have been carried out with varying air densities in the troposphere and stratosphere based on the Geant4 package. The simulation results show a remarkably good agreement with observations. The simulation results also show that the stratosphere air density variation dominates the effects on the muon flux changes while the density variation in the troposphere mainly influences the neutron count variation. This suggests that the long-term variation of muon flux could possibly direct us to a new path to understand the global climate warming trend.

In the 1930s, the Carnegie Institute in Washington DC initiated the construction of cosmic ray observation centres around the world. Cosmic ray activity was recorded using the model C cosmic ray ionization chamber which uses a Lindemann electrometer. Seven of these chambers were constructed at seven stations around the world. These chambers recorded cosmic ray data by projecting the shadow of the electrometer needle onto a continuously moving strip of 60 mm photographic paper. Hour markers were recorded by dimming the lamp for three minutes at the start of each hour, while also grounding the ionization chamber. By grounding the ionization chamber the electrometer needle was returned to the zero position. The photographic paper moved about 25 mm an hour. Approximately 114 station-years of data was recorded between 1935 and 1960 (Hardy, 2006). It is important to digitize these recordings in order to preserve the data for further study of cosmic rays from this time period. This digitization process consists of binarizing digital images of the photographic strip to extract the cosmic ray data. By binarizing these images the data is recorded in an easily usable format for future research. This study focuses on extraction of the cosmic ray data using an adaptive binarization method that is able to cope with a wide variety of images, ranging from images that are almost too bright to distinguish the data lines from the background, to images that are too dark to distinguish the data lines at all. This study starts off with a brief explanation of cosmic rays, how these were recorded before the 1950s and how the rays are recorded today. Two research methodologies were used to create a method to adaptively binarize and extract data from the historic cosmic ray recordings. A literature study of image processing techniques was conducted, focusing specifically on popular adaptive document binarization methods. During the experimental phase of this study, these methods or parts thereof were applied to the data to determine which techniques would give the most accurate results. Experimentation is the primary research methodology. The iterative experimental phase is discussed in detail as an algorithm is formed to successfully binarize and extract the historic cosmic ray data as well as the temperature of the electrometer while recording. The study concludes with an interpretation of the results obtained in the experimental phase. The success of the algorithm is measured by comparing the resulting data graph to the original. The conclusion of this study is that an adaptive method can be applied to historical recordings of cosmic ray activity to extract numerical data from a wide variety of images without any additional user input. / MSc (Computer Science), North-West University, Potchefstroom Campus, 2013

In the 1930s, the Carnegie Institute in Washington DC initiated the construction of cosmic ray observation centres around the world. Cosmic ray activity was recorded using the model C cosmic ray ionization chamber which uses a Lindemann electrometer. Seven of these chambers were constructed at seven stations around the world. These chambers recorded cosmic ray data by projecting the shadow of the electrometer needle onto a continuously moving strip of 60 mm photographic paper. Hour markers were recorded by dimming the lamp for three minutes at the start of each hour, while also grounding the ionization chamber. By grounding the ionization chamber the electrometer needle was returned to the zero position. The photographic paper moved about 25 mm an hour. Approximately 114 station-years of data was recorded between 1935 and 1960 (Hardy, 2006). It is important to digitize these recordings in order to preserve the data for further study of cosmic rays from this time period. This digitization process consists of binarizing digital images of the photographic strip to extract the cosmic ray data. By binarizing these images the data is recorded in an easily usable format for future research. This study focuses on extraction of the cosmic ray data using an adaptive binarization method that is able to cope with a wide variety of images, ranging from images that are almost too bright to distinguish the data lines from the background, to images that are too dark to distinguish the data lines at all. This study starts off with a brief explanation of cosmic rays, how these were recorded before the 1950s and how the rays are recorded today. Two research methodologies were used to create a method to adaptively binarize and extract data from the historic cosmic ray recordings. A literature study of image processing techniques was conducted, focusing specifically on popular adaptive document binarization methods. During the experimental phase of this study, these methods or parts thereof were applied to the data to determine which techniques would give the most accurate results. Experimentation is the primary research methodology. The iterative experimental phase is discussed in detail as an algorithm is formed to successfully binarize and extract the historic cosmic ray data as well as the temperature of the electrometer while recording. The study concludes with an interpretation of the results obtained in the experimental phase. The success of the algorithm is measured by comparing the resulting data graph to the original. The conclusion of this study is that an adaptive method can be applied to historical recordings of cosmic ray activity to extract numerical data from a wide variety of images without any additional user input. / MSc (Computer Science), North-West University, Potchefstroom Campus, 2013

A two-dimensional (2-D) time-dependent cosmic ray modulation model is used to calculate the modulation of cosmic-ray protons and electrons for 11-and 22-year modulation cycles using a compound approach to describe solar cycle related changes in the transport parameters. The compound approach was developed by Ferreira and Potgieter (2004) and incorporates the concept of propagation diffusion barriers, global changes in the magnetic field, time-dependent gradient, curvature and current-sheet drifts, and other basic modulation mechanisms. By comparing model results with 2.5 GV Ulysses observations, for both protons and electrons, it is shown that the compound approach results in computed intensities on a global scale compatible to observations. The model also computes the expected latitudinal dependence, as measured by the Ulysses spacecraft, for both protons and electrons. This is especially highlighted when computed intensities are compared to observations for the different fast latitude scan (FLS) periods. For cosmic ray protons a significant latitude dependence was observed for the first FLS period which corresponded to solar minimum conditions. For the second, which corresponded to solar maximum, no latitude dependence was observed as was the case for the third FLS period, which again corresponded to moderate to minimum solar activity. For the electrons the opposite occurred with only an observable latitude dependence in intensities for the third FLS period. It is shown that the model results in compatible intensities when compared to observations for these periods. Due to the success of the compound approach, it is also possible to compute charge-sign dependent modulation for 2.5 GV protons and electrons. The electron to proton ratio is presented at Earth and along the Ulysses trajectory. Lastly, it is also shown how the modulation amplitude between solar minimum and maximum depends on rigidity. This is investigated by computing cosmic ray intensities for both protons and electrons, not only at 2:5 GV, but also up to 7:5 GV. A refinement for the compound approach at higher rigidities is proposed. / Thesis (M.Sc. (Space Physics))--North-West University, Potchefstroom Campus, 2011.

A two-dimensional (2-D) time-dependent cosmic ray modulation model is used to calculate the modulation of cosmic-ray protons and electrons for 11-and 22-year modulation cycles using a compound approach to describe solar cycle related changes in the transport parameters. The compound approach was developed by Ferreira and Potgieter (2004) and incorporates the concept of propagation diffusion barriers, global changes in the magnetic field, time-dependent gradient, curvature and current-sheet drifts, and other basic modulation mechanisms. By comparing model results with 2.5 GV Ulysses observations, for both protons and electrons, it is shown that the compound approach results in computed intensities on a global scale compatible to observations. The model also computes the expected latitudinal dependence, as measured by the Ulysses spacecraft, for both protons and electrons. This is especially highlighted when computed intensities are compared to observations for the different fast latitude scan (FLS) periods. For cosmic ray protons a significant latitude dependence was observed for the first FLS period which corresponded to solar minimum conditions. For the second, which corresponded to solar maximum, no latitude dependence was observed as was the case for the third FLS period, which again corresponded to moderate to minimum solar activity. For the electrons the opposite occurred with only an observable latitude dependence in intensities for the third FLS period. It is shown that the model results in compatible intensities when compared to observations for these periods. Due to the success of the compound approach, it is also possible to compute charge-sign dependent modulation for 2.5 GV protons and electrons. The electron to proton ratio is presented at Earth and along the Ulysses trajectory. Lastly, it is also shown how the modulation amplitude between solar minimum and maximum depends on rigidity. This is investigated by computing cosmic ray intensities for both protons and electrons, not only at 2:5 GV, but also up to 7:5 GV. A refinement for the compound approach at higher rigidities is proposed. / Thesis (M.Sc. (Space Physics))--North-West University, Potchefstroom Campus, 2011.

ATLAS is a multi-purpose detector for the LHC and will detect proton-proton collisions with center of mass energy of 14 TeV. Part of the central inner detector, the Semi-Conductor Tracker (SCT) barrels, were assembled and tested at Oxford University and later integrated at CERN with the TRT (Transition Radiation Tracker) barrel. The barrel SCT is composed of 4 layers of silicon strip modules with two sensor layers with 80 micro m channel width. The design of the modules and the barrels has been optimized for low radiation length while maintaining mechanical stability, bringing services to the detector, and ensuring a cold and dry environment. The high granularity, high detector efficiency and low noise occupancy (< 5*10^-4) of the SCT will enable ATLAS to have an efficient pattern recognition capability. Due to the binary nature of the SCT read-out, a stable read-out system and the calibration system is of critical importance. SctRodDaq is the online software framework for the calibration and also the physics running of the SCT and has been developed and tested during construction and commissioning of the detector with cosmics. It reliably measures the SCT performance parameters for each of the 6.3*10^6 channels in the SCT, identifies defects and problematic modules and writes them to an offline database for access from Athena, the ATLAS offline software framework. This dataflow chain has been exercised during the cosmics run at CERN, where a 5*10^5 cosmics sample for the combined SCT and TRT detectors was collected with a scintillator based trigger. It is now being commissioned in the ATLAS pit.

This thesis describes several aspects of cosmic ray composition studies using the Utah Fly's Eye and High Resolution Fly's Eye (HiRes) detectors. The Fly's Eye detector utilises the atmospheric fluorescence technique to measure the development of cosmic ray cascades as they pass through the atmosphere. This is complementary to the surface array technique, as used by the Akeno experiment in Japan, which measures the electromagnetic and muon content of air showers at a single observation level. For some time it was thought that Fly's Eye and Akeno gave inconsistent composition results. In Chapter 4 I show that the inconsistency is due, for the most part, to a difference in the assumptions made about hadronic interactions. In Chapter 5 I present analysis of the composition between 10^17 and 10^18 eV using the prototype High Resolution Fly's Eye (HiRes) detector in coincidence with the Michigan Muon Array (MIA). The hybrid nature of these measurements gives us more information about cosmic ray showers than either technique on its own. The consistency or otherwise of the composition measured by the two detectors is discussed. Finally, in Chapter 6, I discuss a method of extracting the total proton-proton cross section from the cosmic ray data. This information is of interest because it is derived at centre of mass energies much higher (by at least an order of magnitude) than those currently accessible by collider experiments. I present a preliminary calculation of the cross section using the HiRes/MIA hybrid data set. / Thesis (Ph.D.)--Department of Physics and Mathematical Physics, 2001.

Thesis (M.Sc.) -- University of Adelaide, School of Chemistry and Physics, Discipline of Physics, 2007. / "February 19, 2007" Bibliography: pages 147-154. Also available in print form.