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STunn:s or X-P.AYS AND COS:-1IC RAYS or G}LAC7IC O IG!N
Leighton Reginald camden, B.Sc.
(HO:1S)
Department of PhysicsA thesis
presented for ti:e degree of Doctor of Philosophy
in the
University of Adelaide March 1971
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40 48 53 56 60 CONTENTS
Page SUMMARY
AC!<N OWLE DGEMENTS it)
CHAPTER 1 OOSKIC RAY ORBITS IN THE INTERPLANETARY MAGNETIC 1 rIELD
1.1 Introduction 1
1.2 The Interplanetary Magnetic Field 2
1. 3 The Calculation of the Basic Orbital Parameters 5 1.4 Application 1 for Cosmic Ray Orbits 10 1.5 Application 2 for Cosmic Ray Orbits 14 1.6 The Accuracy of the Numerical Calculations 18 CHAPTER 2 THE HELlO-ASYMPTOTIC DIRECTIONS 22
2.1 Introduction 22
2.2 The Conditions for which Asymptotic Directions are 23 Calculated
2.3 The Helio-asymptoti c Directions 26
Variations as the Sector Structure Rotates past the Earth 31 CHAPTER 3 TERRESTRIAL EFFECTS OF A GALACTIC ANISOTROP Y
3.1 Introduction
3.2 Solar Effects on a Galactic Anisotropy 3.3 Sidereal Variations, Case 1
3. Sidereal Variations. Case 2
3.5 Modulation by the Rotating Sector Structure The Yearly Average Sidereal Variations
THE ORIGIN-Of-SCATTER COEFFICIENTS THEORY 66
CHAPTER 4 -
4.1 Introduction
The General Analytical Approach
4.3 The F\mdamental Flux Increment, fij (r, T) The Source Function, S
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Page 4.4 Properties of a cone of Directions in Space 75
The Variation with r of the Separation between Two Guiding Centers.
The Separation of Two Trajectories with Equal Pitch Angles.
The Separation of Tva Trajectories with Unequal Pitch Angles.
SUllI1nary •
4.5 The Equation for the Origin-of-Scatter Coefficient
CHAPTER 5 THE ORIGIN-oF-SCATTER COEFFICIENTS - 8a THE CALCULATIONS
5.1 Introduction S8
5.2 The Standard Set of Orbits 99
5.3 Non Orbital Parameters 95
The Spectral Weights of the 1Q Rigidity Intervals.
The Scattering Hean Free Paths.
5.4 The Origin-o f-Scatter Coefficients 99
CHAPTERS COSMIC y VARIATIONS ASSOCIATED WITH RADIAL 107 NUMBER DENSITY GRADIENTS
S.l Introduction 107
6.2 The Long Term Average Diurnal Variation 109 The Second Harmonic in the Theoretical Daily
Variation.
6.3 Short Term Effects in the Diurnal Variation 121 The Effect of Changing the Amplitude of the
Gradient.
The Effect of Ch anging the Rigidity Dependence of the Gradient.
The Effect of a non-linear gradient.
Changes in the Daily Average with Different Mean Free Paths.
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PART B
6.4 128
7.5
9.2
149 Page The Step Gradient - The Forbush Decrease
The Effect of Different Approach Velocities VR, The Profi les at Different Geographic Longitudes.
The Profiles at Different Geographic Latitudes.
Simulatioo of an Observed Event, Increases Prior to For.bush Decreases.
6.S The Rigidity Dependence of the Forbush Decrease 11+1 6.6 The Effects of Departures from the Ideal Magnetic Field 1 2
North-South Anisotropies Associate d with Forbush Decreases.
6.7 Conclusions 146
CHAPTER 7 INSTRUMENTATION FOR TWO EXPERIMENTS TO OBSERVE 149 CELESTIAL X-RAYS
7.1 Introduction
7.2 The Skylark Vehicle 1S1
1.3 Experiment Design Considerations 152
7.4 The Flight III Experiment 160
The Flight IV General Design 7.6
7.7
flight IV Electronics Flight IV Preparation
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CHAPTERS THE e.l Introduction
RESULTS OF THE ROCKET X-RAY EXPERIMEN'l'S 176 176 The Flight III Attitude Solution
B.3 Countrate Analysis 184
8.4 The Source in Cetus 186
8.5 Observations of Other Sources 191
1.93
B1 BLl:.XH?APHY 212
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SUMf.tARy
This thesis discusses the results of research in two independ
ent fields. Part A. presents an analysis of cosmic ray variations using techniques evolved from the calculation of cosmic ray trajectories in a spiral interplanetal"Y 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 ( SOGeV) and for 2 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 asytl1ptotic directions are strongly dependent on the position of the Earth w ithin the sector structure, and when used to derive the sidereal variations associated with a l-way and 2-way isotropy in the galaxy, this
dependence causes a 27 cycle/year (13'5 day period ) modulation in both
the diurnal and s emidiurnal variations. For a l -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/yea:r.
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
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of day T. "origi.'1-of-scatter" coefficients r.( 'r'.T) ;:n-e ....'OllIpUlcO. which relate t he cosmic ray number density between r and I' + AI' 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 a"ld 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 veriaticn is predicted when linear radial gradients
are considered . Forbush decrease profiles are shown to vary stroogly with the effective radial approach velocity of the shock; with
preliminary decreases becol1".ing 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 mech.:mism to account for the U-$ 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 A-ielaide and Tasmania (UAT). Flight III
was partially successful, with two detectors, each of 11- 7 cm2 area. out o f a total sensitive area of 150 cm2• working satisfactorily. Super
position of s veral scans yielded evidence for a new X-ray source
Cet XR-l 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 ::0 :2000 ant, but a vehicle malfunction c ause d the
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experiment to bt.: 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 syst<;ms, and of the calibration and environmental-testing procedures used.