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Type: Thesis
Title: Studies of X-Rays and cosmic rays of galactic origin.
Author: Barnden, Leighton
Issue Date: 1972
School/Discipline: Dept. of Physics
Abstract: This thesis discusses the results of research in two independent fields. Part A. presents an analysis of cosmic ray variations using techniques evolved from the calculation of cosmic ray trajectories in a spiral interplanetary magnetic field model, while Part B discusses the design, preparation and results of two rocket-borne X-ray astronomy experiments. The cosmic ray section divides into a consideration of galactic cosmic rays which (a) reach the Earth without being appreciably scattered, and (b) experience significant scattering eo-route to Earth. In category (a), for selected energies (> 50GeV) and for 24 times of day, asymptotic directions at the edge of the solar cavity are calculated in a 4-sector spiral interplanetary magnetic field model, for cosmic rays which arrive in the equatorial plane. These asymptotic directions are strongly dependent on the position of the Earth within the sector structure, and when used to derive the sidereal variations associated with a l-way and 2-way anisotropy in the galaxy, this dependence causes a 27 cycle/year (13.5 day period ) modulation in both the diurnal and semidiurnal variations. For a 1-way galactic anisotropy the diurnal and semi diurnal variations have approximately the same amplitude and the diurnal variation is further modulated at 1 and 2 cycles/year, and the semidiurnal at 1 cycle/year. In category (b) a new technique is developed which allows the daily variation associated with any arbitrary dependence of cosmic ray number density on heliocentric radius r. to be calculated. For 24 times of day T. "origin-of-scatter" coefficients r.( r.T) are computed, which relate the cosmic ray number density between r and r + Ar to the flux of cosmic rays observed on Earth, which were last-scattered in that region. The number density gradients associated with the average, enhanced and asymmetric diurnal variations and with different Forbush decrease profiles are calculated. In addition, an estimate of the average scattering mean free paths in interplanetary space is given. A small semidiumal variation is predicted when linear radial gradients are considered . Forbush decrease profiles are shown to vary strongly with the effective radial approach velocity of the shock; with preliminary decreases becoming prominant at very low velocities (< 400km/sec). It is shown that the general features of the world-wide variation in the Forbush decrease profiles for a given event can be explained in terms of the approach of a simple step decrease in cosmic ray number density. A mechanism to account for the N-S anisotropy which accompanies some Forbush decreases is suggested, and a brief discussion of further applications is given. The X-ray astronomy section discusses flights III and IV prepared by the Universities of Adelaide and Tasmania (UAT). Flight III was partially successful, with two detectors, each of 11-7 cm2 area, out of a total sensitive area of 150 cm2 working satisfactorily. Superposition of several scans yielded evidence for a new X-ray source Cet XR-1 at high galactic lattitude and an upper limit to the flux from the variable Cen XR-2. Flight IV carried 9 independent detector systems of total area > 2000 cm2, but a vehicle malfunction caused the experiment to be destroyed and there were no results. Apart from the recovered flight III package, the flight IV instrumentation was all newly developed. The factors influencing its general design are discussed and a brief account is given of the on-board pulse-height analysis and associated logic systems, and of the calibration and environmental-testing procedures used.
Dissertation Note: Thesis (Ph.D.) - University of Adelaide, Dept. of Physics, 1972
Keywords: x-rays; cosmic rays; galactic
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