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Transport of low energy neutrons associated with the galactic cosmic ray cascade is analyzed in this dissertation. A benchmark quality analytical algorithm is demonstrated for use with B scRYNTRN, a computer program written by the High Energy Physics Division of N scASA Langley Research Center, which is used to design and analyze shielding against the radiation created by the cascade. B scRYNTRN uses numerical methods to solve the integral transport equations for baryons with the straight-ahead approximation, and numerical and empirical methods to generate the interaction probabilities. The straight-ahead approximation is adequate for charged particles, but not for neutrons. As N scASA Langley improves B scRYNTRN to include low energy neutrons, a benchmark quality solution is needed for comparison. The neutron transport algorithm demonstrated in this dissertation uses the closed-form Green's function solution to the galactic cosmic ray cascade transport equations to generate a source of neutrons. A basis function expansion for finite heterogeneous and semi-infinite homogeneous slabs with multiple energy groups and isotropic scattering is used to generate neutron fluxes resulting from the cascade. This method, called the F(N) method, is used to solve the neutral particle linear Boltzmann transport equation. As a demonstration of the algorithm coded in the programs M scGSLAB and M scGSEMI, neutron and ion fluxes are shown for a beam of fluorine ions at 1000 MeV per nucleon incident on semi-infinite and finite aluminum slabs. Also, to demonstrate that the shielding effectiveness against the radiation from the galactic cosmic ray cascade is not directly proportional to shield thickness, a graph of transmitted total neutron scalar flux versus slab thickness is shown. A simple model based on the nuclear liquid drop assumption is used to generate cross sections for the galactic cosmic ray cascade. The E scNDF/B V database is used to generate the total and scattering cross sections for neutrons in aluminum. As an external verification, the results from M scGSLAB and M scGSEMI were compared to A scNISN/P scC, a routinely used neutron transport code, showing excellent agreement. In an application to an aluminum shield, the F(N) method seems to generate reasonable results.

Applications of in situ cosmogenic nuclides to problems in Quaternary geology require increasingly accurate and precise knowledge of nuclide production rates. Production rates depend on the terrestrial cosmic-ray intensity, which is a function of the elevation and geomagnetic coordinates of a sample site and the geomagnetic field intensity. The main goal of this dissertation is to improve the accuracy of cosmogenic dating by providing better constraints on the spatial variability of production rates.In this dissertation I develop a new scaling model that incorporates the best available cosmic-ray data into a framework that better describes the effects of elevation and geomagnetic shielding on production rates. This model is based on extensive measurements of energetic nucleon fluxes from neutron monitor surveys and on more limited data from low-energy neutron surveys. A major finding of this work is that neutron monitors yield scaling factors different from unshielded proportional counters. To verify that the difference is real I conducted an airborne survey of low-energy neutron fluxes at Hawaii (19.7° N 155.5° W) to compare with a nearby benchmark neutron monitor survey. Our data confirm that the attenuation length is energy dependent and suggest that the scaling factor for energetic nucleons is 10% higher between sea level and 4000 m than for low-energy neutrons at this location. An altitude profile of cosmogenic 36Cl production from lava flows on Mauna Kea, Hawaii, support the use of neutron flux measurements to scale production rates but these data do not have enough precision to confirm or reject the hypothesis of energy-dependent scaling factors.

In the present study we aim to further our understanding of charged particle transport in a magnetized medium. To this end, we perform direct numerical simulations of particle transport in a turbulent magnetic field. From the particle trajectories we calculate diffusion and drift coefficients. In contrast to previous numerical simulations of this nature, we also consider a background magnetic field that contains a gradient perpendicular to the magnetic field direction. By using a non-uniform background magnetic field, we can investigate the simultaneous large scale drift due to the gradient in the background magnetic field and the diffusion due to the turbulence which is superimposed on this background magnetic field. Upon comparison with the simulated diffusion coefficients, the newly proposed weakly non-linear theory (WNLT) of Shalchi et al. (2004b) seems to be the most appropriate theory for the simultaneous description of parallel and perpendicular diffusion over a wide range of fluctuation amplitude and particle rigidity. As for the effect of large scale drift on perpendicular diffusion, we find that under conditions of small amplitude turbulence and/ or high particle rigidity the transport perpendicular to the background field can exhibit super-diffusive behaviour. Diffusive behaviour seems to be recovered for the cases when the turbulence amplitude is sufficiently large and/ or the particle rigidity is sufficiently small. We furthermore find that both the drift coefficient and the drift speed are reduced from their weak scattering counterparts in the presence of scattering, with the reduction becoming more pronounced with increasing turbulence amplitude. For the drift coefficient in particular, the reduction from its weak scattering counterpart behaves differently for the cases in which the background magnetic field is either uniform or non-uniform. For the former case the reduction is predominantly at small rigidities, while for the latter case the reduction is predominantly at large rigidities. The latter result might be of significance for heliospheric modulation models in which the background magnetic field is highly non-uniform. Finally, we use a two-dimensional steadystate cosmic ray modulation model to see how our improved understanding of the underlying transport processes influences the overall cosmic ray modulation in the heliosphere. We conclude that in the absence of a theory which connects large scale drift with small scale diffusion, any statements about the inadequacy of a two-dimensional steady-state modulation model might be premature. / Thesis (Ph.D. (Physics))--North-West University, Potchefstroom Campus, 2006.

This thesis presents theoretical work on the propagation of ultra high energy cosmic rays, from their source to Earth. The different energy loss processes, resulting from cosmic ray interactions with the radiation fields, are addressed. The subsequent uncertainties in the energy loss rates and the effect produced on the arriving cosmic ray spectrum are highlighted. The question of the composition of ultra high energy cosmic rays remains unresolved, with the range of possibilities leading to quite different results in both the secondary fluxes of particles produced through cosmic ray energy loss interactions en route, and the arriving cosmic ray spectra at Earth. A large range of nuclear species are considered in this work, spanning the range of physically motivated nuclear types ejected from the cosmic ray source. The treatment of cosmic ray propagation is usually handled through Monte Carlo simulations due to the stochastic nature of some of the particle physics processes relevant. In this work, an analytic treatment for cosmic ray nuclei propagation is developed. The development of this method providing a deeper understanding of the main components relevant to cosmic ray nuclei propagation, and through its application, a clear insight into the contributing particle physics aspects of the Monte Carlo simulation. A flux of secondary neutrinos, produced as a consequence of cosmic ray energy loss through pion production during propagation, is also expected to be observed at Earth. This spectrum, however, is dependent on several loosely constrained factors such as the radiation field in the infrared region and cosmic ray composition. The range of possible neutrino fluxes obtainable with such uncertainties are discussed in this work. High energy cosmic ray interactions with the radiation fields present within the source may also occur, leading to cosmic ray energy loss before the cosmic ray has even managed to escape. The secondary spectra produced are investigated through the consideration of three candidate sources. A relationship between the degree of photo-disintegration in the source region and the neutrino flux produced through p γ interactions is found.

Cosmic rays at energies 10^18 eV and above are known as Ultra High Energy Cosmic Rays (UHECR). UHECR are charged particles that are accelerated by the biggest accelerators in our universe. Candidate accelerators generating these UHECR are super novas, black holes and neutron stars. But where and what these intergalactic accelerators is at large still unknown. One of the experiments in the forefront of research in this eld is JEM-EUSO, a planed space based telescope for detecting UHECR particles as they enter Earth's atmosphere. Made possible by the advances in photon detectors and light weighted Fresnel lenses. A ground based path nder experiment was carried out in 2015 called EUSO-TA to test the optics and photomultiplier technologies. When the UHECR enters the atmosphere it collides with the atoms generating a number of secondary particles which in turn interacts with other atoms in the atmosphere generating a cascade of secondary particles. These trails are known as Extensive Air Showers (EAS). Mostly electrons are generated and in turn they excites the nitrogen atoms in the atmosphere which generate a isotropic characteristic uorescence light. The JEM-EUSO telescope is designed to detect and measure the photon ux. From the photon ux it will be able to estimate the energy of the initial UHECR. JEM-EUSO will cover the largest area of EAS search and increase statistics of UHECR data. This thesis describes the method and development of algorithms made for EAS analysis and detection based on EUSO-TA data. A simulation of EUSO-TA focal surface was developed, simulating background, stars and EAS. The algorithms developed involves a background subtracting lter, line detection using Hough transform and a neural network for decision making. The Hough transform is used in computer vision and is a method used to detect lines in the pictures. It successfully identi ed both simulated and captured UHECR incoming direction with small errors. Neural network are a machine learning method used classi cation and regression problems. With the use of know example data simulated or real captured data a neural network can without explicit programing it, adjust its parameters to t the data. Based on method called supervised learning. The algorithms was programed in Python and using ROOT software to build the neural network. The resulting algorithm was able to successfully detect simulated data. Test on the EUSO-TA captured data shows a promising result but has to be developed and tested further.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2014-08-12T15:33:42Z No. of bitstreams: 2 Kelen Cristiane Noleto da Costa.pdf: 3124445 bytes, checksum: 8f805839a0c1fe1136fb4081d7be5d18 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2014-08-12T15:33:42Z (GMT). No. of bitstreams: 2 Kelen Cristiane Noleto da Costa.pdf: 3124445 bytes, checksum: 8f805839a0c1fe1136fb4081d7be5d18 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2011-09-30 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Several analysis can be performed using atmospheric muons produced in chain reactions caused by a cosmic ray particle. We can study the muon flux for different parameterizations of the atmosphere, the moon and sun shadowing effect, the muon charge ratio, etc. In this work, we are interested in the atmospheric muon charge ratio (rμ = Nμ+/Nμ−). This ratio has been observed by several experiments, for different energy ranges. The MINOS experiment has determined the muon charge ratio (rμ) in the GeV energy scale using the Near Detector and in the TeV energy scale using the Far Detector. This experiment has observed an increase of the muon charge ratio from 1.27 to 1.37 when the energy of the primary particle changed from ∼ 100 GeV to ∼ 1 TeV. This fact can be explained by the properties of the pions ( ) and the kaons (K). For higher energies, around 10 TeV, the decay of charming hadrons becomes important as a source of atmospheric leptons. Investigating the parameterization given by the Gaisser equation in order to study the intensity of positive and negative muons separately, it is possible to obtain the equation of the pion-kaon ( K) model. Using this model it was made an adjust with the of MINOS Near and Far Detector data, finding the f and fK parameters. These parameters are the fractions that contribute to the production of positive muons coming from de e K, respectively. The experimental values obtained were: f = 0.55 and fK = 0.70. In this work we simulated extensive air showers using the CORSIKA code. Different models that describe the hadronic interactions for high energy particles were used. Our goal was to verify if the models could reproduce the increase of muon charge ratio. This increase is associated with physics involving pion and kaon decays. We found the following parameters: f = 0.547 ± 0.003 and fK = 0.64 ± 0.02 for the QGSJET 01C model, f = 0.604 ± 0.003 and fK = 0.73 ± 0.02 for the SIBYLL model, f = 0.572 ± 0.003 and fK = 0.70 ± 0.02 for the VENUS model, f = 0.545 ± 0.004 and fK = 0.62 ± 0.03 for the QGSJETII model and f = 0.570 ± 0.003 and fK = 0.65 ± 0.02 for the DPMJET model. The increase of the muon charge ratio found in the MINOS data was 7.8%. In our simulation we found an increase of 3.2%, 8.3%, 5.7%, %4.0 and 2.5% for each one of the models, respectively. With these results, it was possible to observe that simulation models also show a significant increase of ratio, when we moved from scale GeV scale for TeV. And of course, this increase is characterized by properties of pions and kaons noting that physics is considered by the codes of models. / Várias análises podem ser feitas a partir de múons atmosféricos produzidos na reação em cadeia provocada por uma partícula de raio cósmico, como o estudo do fluxo de múons para diferentes parametrizações da atmosfera, da sombra da lua e do sol, da razão da carga entre múons atmosféricos. Neste trabalho estamos interessados na razão da carga entre múons atmosféricos (rμ = Nμ+/Nμ−). Essa razão foi determinada por diversos experimentos, para diferentes intervalos de energias. Especificamente, o experimento MINOS determinou a razão (rμ) na escala GeV com o Near Detector e na escala TeV com o Far Detector. Esse experimento observou um aumento da razão de 1,27 para 1,37 com o aumento da energia de ∼100 GeV para ∼ 1 TeV. O aumento dessa razão pode ser entendido a partir das propriedades dos píons ( ) e káons (K). Para energias maiores, cerca de 10 TeV, o decaimento de hádrons charmosos torna-se importante como fonte de léptons atmosféricos. Investigando a parametrização dada pela equação de Gaisser para estudar separadamente a intensidade dos múons positivos e negativos, é possível chegar na equação do modelo píon-káon ( K). Utilizando este modelo, foi feito um ajuste com os dados do MINOS Near e Far Detector, encontrando os parâmetros f e fK. Esses parâmetros são as frações que contribuem para a produção de múons positivos vindos de e K, respectivamente. Os valores experimentais encontrados foram: f = 0,55 e fK = 0,70. Neste trabalho simulamos chuveiros atmosféricos com o código CORSIKA. Diferentes modelos de interações hadrônicas de altas energias foram utilizados. O objetivo foi verificar se os modelos conseguiriam reproduzir o aumento da razão da carga de múons entre GeV e TeV. Esse aumento está associado à física envolvida no decaimento dos píons e káons. Encontramos os seguintes parâmetros: f = 0,550 ± 0,006 e fK = 0,61±0,03 para o modelo QGSJET 01C, f = 0,611±0,004 e fK = 0,67±0,02 para o modelo SIBYLL, f = 0,571 ± 0,005 e fK = 0,70 ± 0,03 para o modelo VENUS, f = 0,547±0,006 e fK = 0,61±0,04 para o modelo QGSJETII e para o modelo DPMJET, f = 0,574±0,004 e fK = 0,63±0,02. O aumento da razão para os dados do experimento MINOS foi de 7,8%; para a nossa simulação o aumento foi de 3,2%; 8,3%; 5,7%; 2,4% e 2,9%; respectivamente. Com esses resultados, foi possível observar que os modelos de simulação também evidenciam um aumento significativo da razão, quando passamos da escala GeV para escala TeV. Esse aumento é caracterizado pelas propriedades dos píons e káons, constatando que essa física é considerada pelos códigos dos modelos.

Sky conditions play an important role in the Earth’s climate system, altering the solar radiation reaching the Earth’s surface and determining the fraction of incoming direct and diffuse radiation. Sky conditions dictate the radiation distribution inside plant canopies and also the carbon dioxide uptake by forests during the growing season. On the long term these diffuse conditions may have a positive influence on forest growth in Northern Britain during the last 50 years. We compared the quantity (amount) and quality (spectral distribution) of direct and diffuse radiation above, inside and below a forest stand under sunny, cloudy and overcast conditions in a thinned Sitka spruce [Picea sitchensis (Bong.) Carr.] forest (28 years, with an leaf area index (LAI) of around 5 m2m-2). Similar radiation properties (sky conditions) were used for analysis of light response and canopy conductance measurements in the same and also in a different spruce forest of the same species (33 years, LAI of around 7 m2 m-2) over the growing season 2008 in order to compare canopy activity under these conditions. In order to integrate short-term and longterm studies, we were looking at how far these conditions are influencing forest growth over several decades. To do so, we used freshly cut tree discs of Sitka spruce from a felled forest (planting year 1953) in southern Scotland and solar direct and diffuse radiation along with other meteorological data from the nearest meteorological station. Our analysis show that the amount and quality of solar radiation is distributed differently inside forest stands under various sky conditions, leading to an enhanced carbon dioxide uptake and canopy stomatal activity under diffuse cloudy and overcast conditions. Furthermore we demonstrated which factors have influenced diffuse radiation distribution over the past 50 years and how these are correlated with forest growth in southern Scotland.

A thesis submitted to the School of Physics, Faculty of Science, University of the Witwatersrand, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, June 2015. / Galaxy clusters are the largest virialised and most recently formed cosmic structures. Their study is therefore a powerful mechanism to probe the large scale properties of the universe. A full understanding of the non-thermal properties of galaxy clusters has not yet been achieved. In particular, the origin of radio halos in galaxy clusters is still a topic of debate today. Several models have been proposed to explain the origin of radio halos but all of these models present some problems either in reproducing observations or in predicting the values of their parameters. Recent observations of radio halos in clusters have shown that in some clusters the morphology of the radio emission appears to be more correlated with the distribution of galaxies than it is with the thermal gas. It has also been observed that while most clusters exhibit a correlation between the radio and X-ray luminosities, there are clear exceptions to this rule. Motivated by these observations, we propose a new theory to explain the origin of radio halos in clusters: that the radio emission observed in clusters is produced by electrons injected by different galaxies and di using in the intra cluster medium. In developing our theory, we study the diffusion of relativistic electrons in galaxies by obtaining a very general solution of the diffusion equation which describes the transport of cosmic rays. This solution allows us to study the spatial, spectral and temporal properties of relativistic electrons and their radio emission for a wide range of cosmic objects. We test this model by applying it to the radio galaxy M51 and reproduce its spatial and spectral properties. We also study the evolution of M51-like galaxies. The model is then applied to study radio halos in clusters of galaxies. We investigate how the properties of these radio halos change when the number and types of sources in a cluster are varied. We compare the results of this model with the observed radio map and density flux spectrum for several galaxy clusters, specifically the low-luminosity cluster CL1446+26 and other clusters with a range of luminosities. Our model provides a very promising explanation of the properties of radio halos in galaxies and clusters of galaxies. The observed properties like the morphology of radio maps in galaxy clusters, the ux spectrum and the correlation between radio and X-ray luminosities, can be reproduced by our model. This is done by considering the combination and evolution of galactic sources having radio properties similar to those of M51. Our model is simple and nevertheless very promising and therefore refining it can lead to a better understanding of the origin of radio halos.

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