The time-dependent modulation of galactic cosmic rays in the heliosphere is studied by computing intensities using a two-dimensional, time-dependent modulation model. The compound approach of Ferreira and Potgieter (2004), which describes changes in the cosmic ray transport coefficients over a solar cycle, is improved by introducing recent theoretical advances in the model. Computed intensities are compared with Voyager 1 and 2, IMP 8 and Ulysses proton observations in search of compatibility. It is shown that this approach gives realistic cosmic ray proton intensities on a global scale at Earth and along both Voyager spacecraft trajectories. The results show that cosmic ray modulation, in particular during the present polarity cycle, is not just determined by changes in the drift coefficient but is also dependent on changes in the diffusion coefficients. Furthermore, a comparison of computations to observations along the Voyager 1 and Voyager 2 trajectories illustrates that the heliosphere is asymmetrical. Assuming the latter, E > 70 MeV and 133-242 MeV cosmic ray proton intensities along Voyager 1 and 2 trajectories are predicted from 2012 onwards. It is shown that the computed intensities along Voyager 1 can increase with an almost constant rate since the spacecraft is close to the heliopause. However, the model shows that Voyager 2 is still under the influence of temporal solar activity changes because of the relatively large distance to the heliopause when compared to Voyager 1. Along the Voyager 2 trajectory the intensities should remain generally constant for the next few years and then should start to steadily increase. It is also found that without knowing the exact location of heliopause and transport parameters one cannot conclude anything about local interstellar spectra. The effect of a dynamic inner heliosheath width on cosmic ray modulation is also studied by implementing a time-dependent termination shock position in the model. This does not lead to improved compatibility with spacecraft observations so that a time-dependent termination shock along with a time-dependent heliopause position is required. The variation of the heliopause position over a solar cycle is found to be smaller compared to that of the termination shock. The model predicts the heliopause and termination shock positions along Voyager 1 in 2012 at 119 AU and 88 AU respectively and along Voyager 2 at 100 AU and 84 AU respectively. / Thesis (PhD (Space Physics))--North-West University, Potchefstroom Campus, 2013

The time-dependent modulation of galactic cosmic rays in the heliosphere is studied by computing intensities using a two-dimensional, time-dependent modulation model. The compound approach of Ferreira and Potgieter (2004), which describes changes in the cosmic ray transport coefficients over a solar cycle, is improved by introducing recent theoretical advances in the model. Computed intensities are compared with Voyager 1 and 2, IMP 8 and Ulysses proton observations in search of compatibility. It is shown that this approach gives realistic cosmic ray proton intensities on a global scale at Earth and along both Voyager spacecraft trajectories. The results show that cosmic ray modulation, in particular during the present polarity cycle, is not just determined by changes in the drift coefficient but is also dependent on changes in the diffusion coefficients. Furthermore, a comparison of computations to observations along the Voyager 1 and Voyager 2 trajectories illustrates that the heliosphere is asymmetrical. Assuming the latter, E > 70 MeV and 133-242 MeV cosmic ray proton intensities along Voyager 1 and 2 trajectories are predicted from 2012 onwards. It is shown that the computed intensities along Voyager 1 can increase with an almost constant rate since the spacecraft is close to the heliopause. However, the model shows that Voyager 2 is still under the influence of temporal solar activity changes because of the relatively large distance to the heliopause when compared to Voyager 1. Along the Voyager 2 trajectory the intensities should remain generally constant for the next few years and then should start to steadily increase. It is also found that without knowing the exact location of heliopause and transport parameters one cannot conclude anything about local interstellar spectra. The effect of a dynamic inner heliosheath width on cosmic ray modulation is also studied by implementing a time-dependent termination shock position in the model. This does not lead to improved compatibility with spacecraft observations so that a time-dependent termination shock along with a time-dependent heliopause position is required. The variation of the heliopause position over a solar cycle is found to be smaller compared to that of the termination shock. The model predicts the heliopause and termination shock positions along Voyager 1 in 2012 at 119 AU and 88 AU respectively and along Voyager 2 at 100 AU and 84 AU respectively. / Thesis (PhD (Space Physics))--North-West University, Potchefstroom Campus, 2013

名古屋大学年代測定総合研究センターシンポジウム報告

A three-dimensional (3D) steady-state electron modulation model based on Parker (1965) transport equation is applied to study the modelling of – 7 MeV galactic and Jovian electrons in the inner heliosphere. The latter is produced within Jupiter's magnetosphere which is situated at - 5 AU in the ecliptic plane. The heliospheric propagation of these particles is mainly described by the heliospheric diffusion tensor. Some elements of the tensor, such as the diffusion coefficient in the azimuthal direction, which were neglected in the previous two-dimensional modulation studies are investigated to account for the three-dimensional transport of Jovian electrons. Different anisotropic solar wind speed profiles that could represent solar minimum conditions were modelled and their effects were illustrated by computing the distribution of 7 MeV Jovian electrons in the equatorial regions. In particular, the electron intensity time-profile along the Ulysses spacecraft trajectory was calculated for these speed profiles and compared to the 3-10 MeV electron flux observed by the Kiel Electron Telescope (KET) on board the Ulysses spacecraft from launch (1990) up to end of its first out-of-ecliptic orbit (2000). It was found that the model solution computed with the solar wind profile previously assumed for typical solar minimum conditions produced good compatibility with observations up to 1998. After 1998 all model solutions deviated completely from the observations. In this study, as a further attempt to model KET observations more realistically, a new relation is established between the latitudinal dependence of the solar wind speed and the perpendicular polar diffusion. Based on this relation, a transition of an average solar wind speed from solar minimum conditions to intermediate solar activity and to solar maximum conditions was modelled based on the assumption of the time-evolution of large polar coronal holes and were correlated to different scenarios of the enhancement of perpendicular polar diffusion. Effects of these scenarios were illustrated, as a series of steady-state solutions, on the computed 7 MeV Jovian and galactic electrons in comparison with the 3-10 MeV electron observed by the KET instrument from the period 1998 up to the end of 2003. Subsequent effects of these scenarios were also shown on electron modulation in general. It was found that this approach improved modelling of the post-1998 discrepancy between the model and KET observations but it also suggested the need for a time-dependent 3D electron modulation model to describe modulation during moderate to extreme solar maximum conditions. / Thesis (M.Sc.)--North-West University, Potchefstroom Campus, 2004.

The interest in the role of the solar wind termination shock (TS) and heliosheath in cosmic ray (CR) modulation studies has increased sigm6cantly as the Voyager 1 and 2 spacecraft approach the estimated position of the TS. For this work the modulation of galactic CR protons, anti-protons, electrons with a Jovian source, positrons, Helium, and anomalous protons and Helium, and the consequent charge-sign dependence, are studied with an improved and extended two-dimensional numerical CR modulation model including a TS with diffusive shock acceleration, a heliosheath and drifts. The modulation is computed using improved local interstellar spectra (LIS) for almost all the species of interest to this study and new fundamentally derived diffusion coefficients, applicable to a number of CR species during both magnetic polarity cycles of the Sun. The model also allows comparisons of modulation with and without a TS and between solar minimum and moderate maximum conditions. The modulation of protons and Helium with their respective anomalous components are also studied to establish the consequent charge-sign dependence at low energies and the influence on the computed p/p, e-/p, and e-/He. The level of modulation in the simulated heliosheath, and the importance of this modulation 'barrier' and the TS for the different species are illustrated. From the computations it is possible to estimate the ratio of modulation occurring in the heliosheath to the total modulation between the heliopause and Earth for the mentioned species. It has been found that the modulation in the heliosheath depends on the particle species, is strongly dependent on the energy of the CRs, on the polarity cycle and is enhanced by the inclusion of the TS. The computed modulation for the considered species is surprisingly different and the heliosheath is important for CR modulation, although 'barrier' modulation is more prominent for protons, anti-protons and Helium, while the heliosheath cannot really be considered a modulation 'barrier' for electrons and positrons above energies of ~150 MeV. The effects of the TS on modulation are more pronounced for polarity cycles when particles are drifting primarily in the equatorial regions of the heliosphere along the heliospheric current sheet to the Sun, e.g. the A < 0 polarity cycle for protons, positrons, and Helium, and the A > 0 polarity cycle for electrons and anti-protons. This study also shows that the proton and Helium LIS may not be known at energies <~ 200 MeV until a spacecraft actually approaches the heliopause because of the strong modulation that occurs in the heliosheath, the effect of the TS, and the presence of anomalous protons and Helium. For anti-protons, in contrast, these effects are less pronounced. For positrons, with a completely different shape LIS, the modulated spectra have very mild energy dependencies <~ 300 MeV, even at Earth, in contrast to the other species. These characteristic spectral features may be helpful to distinguish between electron and positron spectra when they are measured near and at Earth. These simulations can be of use for future missions to the outer heliosphere and beyond. / Thesis (Ph.D. (Physics))--North-West University, Potchefstroom Campus, 2004.

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.

Many ATLAS analyses study events with muons in them including those searching for the Higgs boson and new physics. Cosmics muons, however, can also occasionally enter the detector and mimic the trajectory of a muon from one of the collisions produced by CERN’s Large Hadron Collider. By understanding the different ways ATLAS triggers on, collects, reconstructs, and analyses data from cosmic rays and collisions, the flux of cosmic muons with transverse momenta above 20 GeV in the central region of the detector was measured to be 1.34 ± 0.06 (stat.) s^−1 m^−2 . At the same time the cosmic muon charge ratio has been measured to be 1.3 ± 0.1 (stat.). This measurement of the cosmic muon flux in ATLAS is the first step in quantifying the sizes of the cosmic muon backgrounds to various physics analyses that look for events with muons. / Graduate

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a 1.8 meter Cassegrain telescope that operates in three bands (250, 350, and 500 μm), each with 30% bandwidth. The detection system is comprised of 280 silicon-nitride micromesh bolometers distributed on three focal plane arrays with 30”, 42”, and 60” FWHM (full width at half max) beam sizes, respectively. BLAST's goal is to study the evolutionary history and processes associated with star formation. Earth's atmosphere is opaque to submillimeter radiation and astronomical observations in this wavelength are best conducted at high altitudes. BLAST is designed to be flown above 99.5% of the atmosphere on a stratospheric balloon. BLAST has made three scientific flights and this thesis covers the last two. The second flight was made in 2006 from McMurdo, Antarctica and studied the evolutionary history and processes associated with star formation. For the third flight, BLAST was reconfigured as a polarimeter (BLAST-Pol) and was also launched from McMurdo in December 2010. BLAST-Pol's objective is to determine what role, if any, magnetic fields play in star formation. This thesis will describe the BLAST-Pol instrument and provide a summery of key observations made by the 2006 flight.

The energy deposition characteristics of heavy ions vary substantially compared to those of photons. Many radiation biology studies have compared the damaging effects of different types of radiation to establish relative biological effectiveness among them. These studies are dependent on cell type, biological endpoint, radiation type, dose, and dose rate. The radiation field found in space is much more complicated than that simulated in most experiments, both from a point of dose-rate as well as the highly mixed field of radiative particles encompassing a broad spectrum of energies. To establish better estimates for radiation risks on long-term, deep space missions, the damaging ability of heavy ions requires further understanding. Track structure studies provide significant details about the spatial distribution of energy deposition events in and around the sensitive targets of a mammalian cell. The damage imparted by one heavy ion relative to another can be established by modeling the track structures of ions that make up the galactic cosmic ray (GCR) spectrum and emphasizing biologically relevant target geometries. This research was undertaken to provide a better understanding of the damaging ability of GCR at the cellular level. By comparing ions with equal stopping power values, the differences in track structure will illuminate variations in cell particle traversals and ionization density within cell nuclei. For a cellular target, increased particle traversals, along with increased ionization density, are key identifiers for increased damaging ability. Performing Monte Carlo simulations with the computer code, FLUKA, this research will provide cellular dosimetry data and detail the track structure of the ions. As shown in radiobiology studies, increased ionizations within a cell nucleus generally lead to increased DNA breaks and increased free radical production, resulting in increased carcinogenesis and cell death. The spatial distribution of dose surrounding ions tracks are compared for inter- and intracellular regions. A comparison can be made for many different ions based upon dose and particle fluence across those different regions to predict relative damaging ability. This information can be used to improve estimates for radiation quality and dose equivalent from the space radiation environment.