The existence of a Fisk-type heliospheric magnetic field (HMF) is one of the most debated questions in cosmic-ray modulation. Recently, Burger and Hitge [2004] developed a divergence-free Fisk-Parker hybrid magnetic field model to demonstrate the behaviour of cosmic rays in the heliosphere due to such a field. This approach has been refined and the properties of the consequent field are investigated. It is found that randomly directed magnetic field diffusion in and above the photosphere significantly influences the solar magnetic field both at the solar poles and near the polar coronal hole boundary. The solar cycle dependence of this field is investigated, a study which is of particular importance for studies of the long-term behaviour of cosmic rays, such as those undertaken at the SANAE base in Antarctica. The amplitudes of the 26-day recurrent cosmic-ray variations are modelled as function of both latitudinal gradient and heliolatitude and are found to agree qualitatively and in some cases quantitatively with the observational results reported by Zhang 119971 and Paizis et al. 119991. Although magnetic field data do not clearly indicate the existence of the Fisk field [see, e.g., Fursyth et al., 20021, this study supports the existence of a Fisk-type HMF. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2006.

Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2008.

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.

Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2008.

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 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.

This study set out to examine the levels of galactic cosmic radiation exposure to Australian aircrew during routine flight operations, with particular attention to the high southern latitude flights between Australia and South Africa. Latitudes as high as 65?? South were flown to gain the data and are typical of the normal flight routes flown between Sydney and Johannesburg on a daily basis. In achieving this objective it became evident that suitable commercially available radiation monitoring equipment was not readily available and scientific radiation monitors were sourced from overseas research facilities to compliment my own FH4lB and Liulin monitors provided by UNSW. At the same time it became apparent that several predictive codes had been developed to attempt to model the radiation doses received by aircrew based on flight route, latitudes and altitudes. Further, it became apparent that these codes had not been subjected to verification at high southern latitudes and that they had not been validated for the effects of solar particle events. Initially measurements were required at the high latitudes followed by mid-latitude data to further balance the PCAIRE code to ensure reasonableness of results for both equatorial and high latitudes. Whilst undertaking this study new scientific monitors became available which provided an opportunity to observe comparative data and results. The Liulin, QDOS and a number of smaller personal dosimeters were subsequently obtained and evaluated. This appears to be the first time that such an extensive cross comparison of these monitors has been conducted over such a wide range of latitudes and altitudes. During the course of this study a fortuitous encounter with GLE 66 enabled several aspects of code validation to be examined, namely the inability of predictive codes to estimate the increased dose associated with a GLE or the effects of a Forbush decrease on the code results. Finally I review the known biological effects as discussed by numerous authors based on current epidemiological studies, with a view to high-lighting were the advent of future technology in aviation may project aircrew dose levels.

Bibliography : leaves 1-6 of 2nd sequence / vii, 104, [28] 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, 1993

Thesis (Ph.D.)--Tufts University, 2002. / Adviser: Alexander Vilenkin. Submitted to the Dept. of Physics. Includes bibliographical references (leaves 95-98). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (Ph. D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1993. / Includes bibliographical references (leaves 1-6 of 2nd sequence).