Due to the research on cosmic-rays in the 1930's, the Carnegie Institute in Washington DC instigated the construction of cosmic-ray observation centers around the world. Cosmic-ray activity was recorded using the model C cosmic-ray ionization chamber which uses a Lindemann electrometer. The shadow of the electrometer needle was projected 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. Six ionization chambers were built and installed at six stations around the world. Approximately 114 station-years of data were recorded. Photographic paper moved about 25 mm an hour giving approximately a 25 km strip of photographic record. It is important to digitize these recordings in order to preserve them for further study of cosmic-rays from this time period. The digitizing of cosmic-ray recordings involves the process of transforming the recording image into numbers. Binarizing these recordings will also preserve it in a clear format enabling future research. This study is an attempt to prove that these historic cosmic-ray recordings can be digitized by using image processing techniques. Each foreground element of the recordings; the hour markers, calibration lines and data sequence is segmented. By using these segmented images, the recordings are digitized into meaningful numbers. The study begins with a brief introduction on cosmic-rays as they are recorded today, and how they were recorded before the 1950's. Important events in the area of cosmicrays, ground level enhancements (GLE's), are also introduced. Four of these GLE's were only recorded by the old model C cosmic ray ionization chambers. To show that it is indeed possible to digitize the historic cosmic-ray recordings, two research methodologies are used: A literature study of image processing techniques thought to be helpful in segmenting the foreground elements of the recordings and experimentation with these techniques. Experimentation is the primary research methodology. Existing techniques are used and adapted to segment the foreground elements of the recordings. New techniques are also developed. The iterative experimental phase is discussed in detail as an algorithm is formed to successfully digitize the historic cosmic-ray recordings. The study concludes with an interpretation of the results obtained in the experimental phase. The success of the algorithm is measured and future studies are introduced. In the end it is indeed shown that historic cosmic-ray recordings can be digitized by implementing image processing techniques. / Thesis (M.Sc. (Computer Science))--North-West University, Potchefstroom Campus, 2010.

Due to the research on cosmic-rays in the 1930's, the Carnegie Institute in Washington DC instigated the construction of cosmic-ray observation centers around the world. Cosmic-ray activity was recorded using the model C cosmic-ray ionization chamber which uses a Lindemann electrometer. The shadow of the electrometer needle was projected 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. Six ionization chambers were built and installed at six stations around the world. Approximately 114 station-years of data were recorded. Photographic paper moved about 25 mm an hour giving approximately a 25 km strip of photographic record. It is important to digitize these recordings in order to preserve them for further study of cosmic-rays from this time period. The digitizing of cosmic-ray recordings involves the process of transforming the recording image into numbers. Binarizing these recordings will also preserve it in a clear format enabling future research. This study is an attempt to prove that these historic cosmic-ray recordings can be digitized by using image processing techniques. Each foreground element of the recordings; the hour markers, calibration lines and data sequence is segmented. By using these segmented images, the recordings are digitized into meaningful numbers. The study begins with a brief introduction on cosmic-rays as they are recorded today, and how they were recorded before the 1950's. Important events in the area of cosmicrays, ground level enhancements (GLE's), are also introduced. Four of these GLE's were only recorded by the old model C cosmic ray ionization chambers. To show that it is indeed possible to digitize the historic cosmic-ray recordings, two research methodologies are used: A literature study of image processing techniques thought to be helpful in segmenting the foreground elements of the recordings and experimentation with these techniques. Experimentation is the primary research methodology. Existing techniques are used and adapted to segment the foreground elements of the recordings. New techniques are also developed. The iterative experimental phase is discussed in detail as an algorithm is formed to successfully digitize the historic cosmic-ray recordings. The study concludes with an interpretation of the results obtained in the experimental phase. The success of the algorithm is measured and future studies are introduced. In the end it is indeed shown that historic cosmic-ray recordings can be digitized by implementing image processing techniques. / Thesis (M.Sc. (Computer Science))--North-West University, Potchefstroom Campus, 2010.

The solar minimum of 2009 has been identified as an exceptional event with regard to cosmic ray (CR)modulation, since conditions in the heliosphere have reached unprecedented quiet levels. This unique minimum has been observed by the Earth–orbiting satellite, PAMELA, launched in June, 2006, from which vast sets of accurate proton and electron preliminary observations have been made available. These simultaneous measurements from PAMELA provide the ideal opportunity to conduct an in–depth study of CR modulation, in particular charge–sign dependent modulation. In utilizing this opportunity, a three–dimensional, steady–state modulation model was used to reproduce a selection of consecutive PAMELA proton and electron spectra from 2006 to 2009. Thiswas done by assuming full drifts and simplified diffusion coefficients, where the rigidity dependence and absolute value of themean free paths for protons and electrons were sequentially adjusted below 3 GV and 300 MV, respectively. Care has been taken in calculating yearly–averaged current–sheet tilt angle and magnetic field values that correspond to the PAMELA spectra. Following this study where the numerical model was used to investigate the individual effects resulting from changes in the tilt angle, diffusion coefficients, and global drifts, it was found that all these modulation processes played significant roles in contributing to the total increase in CR intensities from 2006 to 2009, as was observed by PAMELA. Furthermore, the effect that drifts has on oppositely charged particles was also evident from the difference between the peak–shaped time profiles of protons and the flatter time profiles of electrons, as is expected for an A < 0 polarity cycle. Since protons, which drift into the heliosphere along the heliospheric current–sheet, haven’t yet reached maximum intensity levels by 2008, their intensities increased notably more than electrons toward the end of 2009. The time and energy dependence of the electron to proton ratios were also studied in order to further illustrate and quantify the effect of drifts during this remarkable solar minimum period. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2012.

The solar minimum of 2009 has been identified as an exceptional event with regard to cosmic ray (CR)modulation, since conditions in the heliosphere have reached unprecedented quiet levels. This unique minimum has been observed by the Earth–orbiting satellite, PAMELA, launched in June, 2006, from which vast sets of accurate proton and electron preliminary observations have been made available. These simultaneous measurements from PAMELA provide the ideal opportunity to conduct an in–depth study of CR modulation, in particular charge–sign dependent modulation. In utilizing this opportunity, a three–dimensional, steady–state modulation model was used to reproduce a selection of consecutive PAMELA proton and electron spectra from 2006 to 2009. Thiswas done by assuming full drifts and simplified diffusion coefficients, where the rigidity dependence and absolute value of themean free paths for protons and electrons were sequentially adjusted below 3 GV and 300 MV, respectively. Care has been taken in calculating yearly–averaged current–sheet tilt angle and magnetic field values that correspond to the PAMELA spectra. Following this study where the numerical model was used to investigate the individual effects resulting from changes in the tilt angle, diffusion coefficients, and global drifts, it was found that all these modulation processes played significant roles in contributing to the total increase in CR intensities from 2006 to 2009, as was observed by PAMELA. Furthermore, the effect that drifts has on oppositely charged particles was also evident from the difference between the peak–shaped time profiles of protons and the flatter time profiles of electrons, as is expected for an A < 0 polarity cycle. Since protons, which drift into the heliosphere along the heliospheric current–sheet, haven’t yet reached maximum intensity levels by 2008, their intensities increased notably more than electrons toward the end of 2009. The time and energy dependence of the electron to proton ratios were also studied in order to further illustrate and quantify the effect of drifts during this remarkable solar minimum period. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2012.

The launch of the Large Area Telescope (LAT), on board the Fermi spacecraft, has led to an astounding increase in the number of known y-ray pulsars. This wealth of new data has generated renewed interest in the field of pulsar astrophysics, with many of the established geometric models for y-ray emission coming under fresh scrutiny. In this work the outer gap (OG) and two-pole caustic (TPC) geometric -ray models are employed alongside a simple empirical radio model to obtain best-fit light curves by eye for six single-peak Fermi LAT pulsars first reported by Weltevrede et al. (2010). These best-fit solutions aim to reproduce both the shapes of the radio and y-ray light curves, and the radio-to- phase lag. A parameter study of the geometric models is also conducted, and the increased qualitative understanding of these models thus gained is then employed to obtain the best fits possible. The combination of radio and -ray models is found to be remarkably powerful in constraining the values of the geometric parameters of the individual pulsars: the inclination and observer angles. Generally the constraints implied by the radio model act perpendicularly to those implied by the y-ray models, thus yielding smaller solution contours. The constraints on the geometric parameters obtained for the six Fermi LAT pulsars in question agree quite well with those obtained by Weltevrede et al. (2010). This agreement is remarkable considering that the approach employed in this study is independent from the one employed by Weltevrede et al. (2010). The errors obtained in this study on the values of the inclination angle for each pulsar are generally smaller than those obtained by Weltevrede et al. (2010). As a secondary result, the value of the flux correction factor, which is a measure of how well the observed y-ray energy flux of the pulsar correlates with the overall y-ray energy flux, is constrained for each pulsar. / MSc (Space Physics), North-West University, Potchefstroom Campus, 2014

The launch of the Large Area Telescope (LAT), on board the Fermi spacecraft, has led to an astounding increase in the number of known y-ray pulsars. This wealth of new data has generated renewed interest in the field of pulsar astrophysics, with many of the established geometric models for y-ray emission coming under fresh scrutiny. In this work the outer gap (OG) and two-pole caustic (TPC) geometric -ray models are employed alongside a simple empirical radio model to obtain best-fit light curves by eye for six single-peak Fermi LAT pulsars first reported by Weltevrede et al. (2010). These best-fit solutions aim to reproduce both the shapes of the radio and y-ray light curves, and the radio-to- phase lag. A parameter study of the geometric models is also conducted, and the increased qualitative understanding of these models thus gained is then employed to obtain the best fits possible. The combination of radio and -ray models is found to be remarkably powerful in constraining the values of the geometric parameters of the individual pulsars: the inclination and observer angles. Generally the constraints implied by the radio model act perpendicularly to those implied by the y-ray models, thus yielding smaller solution contours. The constraints on the geometric parameters obtained for the six Fermi LAT pulsars in question agree quite well with those obtained by Weltevrede et al. (2010). This agreement is remarkable considering that the approach employed in this study is independent from the one employed by Weltevrede et al. (2010). The errors obtained in this study on the values of the inclination angle for each pulsar are generally smaller than those obtained by Weltevrede et al. (2010). As a secondary result, the value of the flux correction factor, which is a measure of how well the observed y-ray energy flux of the pulsar correlates with the overall y-ray energy flux, is constrained for each pulsar. / MSc (Space Physics), North-West University, Potchefstroom Campus, 2014

The Voyager 1 spacecraft is now about 25 AU beyond the heliospheric termination shock and soon it should encounter the outer boundary of the heliosphere, the heliopause. This is set to be at 120 AU in the modulation model used for this study. This implies that Voyager 1, and soon afterwards also Voyager 2, should be able to measure the heliopause spectrum, to be interpreted as the lowest possible local interstellar spectrum, for low energy galactic electrons (1 MeV to 120 MeV). This could give an answer to a long outstanding question about the spectral shape (energy dependence) of the galactic electron spectrum at these low energies. These in situ electron observations from Voyager 1, until the year 2010 when it was already beyond 112 AU, are used for a comparative study with a comprehensive three dimensional numerical model for the solar modulation of galactic electrons from the inner to the outer heliosphere. A locally developed steady state modulation model which numerically solves the relevant heliospheric transport equation is used to compute and study modulated electron spectra from Earth up to the heliopause. The issue of the spectral shape of the local interstellar spectrum at these low energies is specifically addressed, taking into account modulation in the inner heliosheath, up to the heliopause, including the effects of the transition of the solar wind speed from supersonic to subsonic in the heliosheath. Modulated electron spectra from the inner to the outer heliosphere are computed, together with radial and latitudinal profiles, focusing on 12 MeV electrons. This is compared to Voyager 1 observations for the energy range 6–14 MeV. A heliopause electron spectrum is computed and presented as a new plausible local interstellar spectrum from 30 GeV down to 10 MeV. The comparisons between model predictions and observations from Voyager 1 and at Earth (e.g. from the PAMELA mission and from balloon flights) and in the inner heliosphere (e.g. from the Ulysses mission) are made. This enables one to make conclusions about diffusion theory applicable to electrons in the heliosphere, in particular the rigidity dependence of diffusion perpendicular and parallel to the local background solar magnetic field. A general result is that the rigidity dependence of both parallel and perpendicular diffusion coefficients needs to be constant below P < 0.4 GV and only be allowed to increase above this rigidity to assure compatibility between the modeling and observations at Earth and especially in the outer heliosphere. A modification in the radial dependence of the diffusion coefficients in the inner heliosheath is required to compute realistic modulation in this region. With this study, estimates of the intensity of low energy galactic electrons at Earth can be made. A new local interstellar spectrum is computed for these low energies to improve understanding of the modulation galactic electrons as compared to previous results described in the literature. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2012.

The Voyager 1 spacecraft is now about 25 AU beyond the heliospheric termination shock and soon it should encounter the outer boundary of the heliosphere, the heliopause. This is set to be at 120 AU in the modulation model used for this study. This implies that Voyager 1, and soon afterwards also Voyager 2, should be able to measure the heliopause spectrum, to be interpreted as the lowest possible local interstellar spectrum, for low energy galactic electrons (1 MeV to 120 MeV). This could give an answer to a long outstanding question about the spectral shape (energy dependence) of the galactic electron spectrum at these low energies. These in situ electron observations from Voyager 1, until the year 2010 when it was already beyond 112 AU, are used for a comparative study with a comprehensive three dimensional numerical model for the solar modulation of galactic electrons from the inner to the outer heliosphere. A locally developed steady state modulation model which numerically solves the relevant heliospheric transport equation is used to compute and study modulated electron spectra from Earth up to the heliopause. The issue of the spectral shape of the local interstellar spectrum at these low energies is specifically addressed, taking into account modulation in the inner heliosheath, up to the heliopause, including the effects of the transition of the solar wind speed from supersonic to subsonic in the heliosheath. Modulated electron spectra from the inner to the outer heliosphere are computed, together with radial and latitudinal profiles, focusing on 12 MeV electrons. This is compared to Voyager 1 observations for the energy range 6–14 MeV. A heliopause electron spectrum is computed and presented as a new plausible local interstellar spectrum from 30 GeV down to 10 MeV. The comparisons between model predictions and observations from Voyager 1 and at Earth (e.g. from the PAMELA mission and from balloon flights) and in the inner heliosphere (e.g. from the Ulysses mission) are made. This enables one to make conclusions about diffusion theory applicable to electrons in the heliosphere, in particular the rigidity dependence of diffusion perpendicular and parallel to the local background solar magnetic field. A general result is that the rigidity dependence of both parallel and perpendicular diffusion coefficients needs to be constant below P < 0.4 GV and only be allowed to increase above this rigidity to assure compatibility between the modeling and observations at Earth and especially in the outer heliosphere. A modification in the radial dependence of the diffusion coefficients in the inner heliosheath is required to compute realistic modulation in this region. With this study, estimates of the intensity of low energy galactic electrons at Earth can be made. A new local interstellar spectrum is computed for these low energies to improve understanding of the modulation galactic electrons as compared to previous results described in the literature. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2012.

The transport of cosmic rays in the heliosphere is studied by making use of a newly developed modulation model. This model employes stochastic differential equations to numerically solve the relevant transport equation, making use of this approach’s numerical advantages as well as the opportunity to extract additional information regarding cosmic ray transport and the processes responsible for it. The propagation times and energy losses of galactic electrons and protons are calculated for different drift cycles. It is confirmed that protons and electrons lose the same amount of rigidity when they experience the same transport processes. These particles spend more time in the heliosphere, and also lose more energy, in the drift cycle where they drift towards Earth mainly along the heliospheric current sheet. The propagation times of galactic protons from the heliopause to Earth are calculated for increasing heliospheric tilt angles and it is found that current sheet drift becomes less effective with increasing solar activity. Comparing calculated propagation times of Jovian electrons with observations, the transport parameters are constrained to find that 50% of 6 MeV electrons measured at Earth are of Jovian origin. Charge-sign dependent modulation is modelled by simulating the proton to anti-proton ratio at Earth and comparing the results to recent PAMELA observations. A hybrid cosmic ray modulation model is constructed by coupling the numerical modulation model to the heliospheric environment as simulated by a magneto-hydrodynamic model. Using this model, it is shown that cosmic ray modulation persists beyond the heliopause. The level of modulation in this region is found to exhibit solar cycle related changes and, more importantly, is independent of the magnitude of the individual diffusion coefficients, but is rather determined by the ratio of parallel to perpendicular diffusion. / PhD (Space Physics), North-West University, Potchefstroom Campus, 2013

The transport of cosmic rays in the heliosphere is studied by making use of a newly developed modulation model. This model employes stochastic differential equations to numerically solve the relevant transport equation, making use of this approach’s numerical advantages as well as the opportunity to extract additional information regarding cosmic ray transport and the processes responsible for it. The propagation times and energy losses of galactic electrons and protons are calculated for different drift cycles. It is confirmed that protons and electrons lose the same amount of rigidity when they experience the same transport processes. These particles spend more time in the heliosphere, and also lose more energy, in the drift cycle where they drift towards Earth mainly along the heliospheric current sheet. The propagation times of galactic protons from the heliopause to Earth are calculated for increasing heliospheric tilt angles and it is found that current sheet drift becomes less effective with increasing solar activity. Comparing calculated propagation times of Jovian electrons with observations, the transport parameters are constrained to find that 50% of 6 MeV electrons measured at Earth are of Jovian origin. Charge-sign dependent modulation is modelled by simulating the proton to anti-proton ratio at Earth and comparing the results to recent PAMELA observations. A hybrid cosmic ray modulation model is constructed by coupling the numerical modulation model to the heliospheric environment as simulated by a magneto-hydrodynamic model. Using this model, it is shown that cosmic ray modulation persists beyond the heliopause. The level of modulation in this region is found to exhibit solar cycle related changes and, more importantly, is independent of the magnitude of the individual diffusion coefficients, but is rather determined by the ratio of parallel to perpendicular diffusion. / PhD (Space Physics), North-West University, Potchefstroom Campus, 2013