An investigation of the radio emission by the planet Jupiter on 18 Mc/s & 22 Mc/s
- Authors: Gruber, Georg Maria
- Date: 1963
- Subjects: Radio astronomy , Jupiter (Planet) -- Observations , Radio sources (Astronomy)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5524 , http://hdl.handle.net/10962/d1012113 , Radio astronomy , Jupiter (Planet) -- Observations , Radio sources (Astronomy)
- Description: This thesis describes the investigation carried out of the radio noise emitted by the planet Jupiter on 18 Mc/s and 22 Mc/s. Chapter I gives a brief introduction and outlines radioastronomical as well as astronomical ideas concerning Jupiter. A detailed survey of the research done to date including some of the hypotheses formulated by previous workers is presented in Chapter II . Chapter III deals with the apparatus used in this research. Two similar sets of apparatus were used. The aerials were folded dipoles. The signals were fed to the receiver, an R 206 , via a 300 ohm impedance line. To increase the gain an extra I -F. stage was included. This gave a gain of better than a 120 dB. To match the signals into the recorder a cathode follower was used. The operating procedure appears in the fourth chapter. The results obtained are discussed and tabulated at the end of the chapter. They agree with the findings made by previous workers, within the experimental limit. Histograms of the occurrence probability versus the revised System III coordinates are presented for each frequency and compared to previous ones. The final chapter contains the author ' s interpretation of the observed effects. A model based on a radiation analogous to the Cerenkov effect is found to be not inconsistent with the available data . Ending the chapter suggestions for further research are made.
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- Date Issued: 1963
Some properties of a model F1 layer of the ionosphere
- Authors: De Jager, Gerhard
- Date: 1963
- Subjects: Ionosphere , Ionospheric electron density
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5515 , http://hdl.handle.net/10962/d1011046 , Ionosphere , Ionospheric electron density
- Description: The present work was initially aimed at providing an explanation for some of the phenomena that occur in the ionosphere at sunrise. The approach that was taken was to determine the changes that take place on a theoretical model of the ionosphere and then to compare these with observations. A prerequisite for this approach was a theoretical model that would show, among other things, a bifurcation of the F layer during daytime without making unjustified arbitrary assumptions. The absence of such a model, particularly as far as non-equilibrium conditions are concerned, resulted in the present attempt to provide such a model for the F1 region.
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- Date Issued: 1963
The design and construction of a recording spectrometer for the measurement of fluorescence excitation spectra in the vacuum ultra-violet region
- Authors: Davidson, A T
- Date: 1963
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:21177 , http://hdl.handle.net/10962/6761
- Description: Summary: A recording spectrometer for the measurement of fluorescence excitation spectra in the visible and ultra-violet regions of the spectrum is described. A direct method of modulating the hydrogen light source of the spectrograph is presented, whereby the discharge is driven by an A.C. power oscillator. The use of tuned amplifiers in the detecting unit is investigated as a means of eliminating the D.C. component of the dark current. Aspects of the modulation method are discussed. Fluorescence and energy transfer in aromatic hydrocarbon is discussed with particular regard to anthracene. Some absorption, fluorescence, excitation and reflection spectra of anthracene obtained by previous workers are presented9 together with Tables listing the wavelengths of principal maxima for the above spectra published in the literature. Features of the excitation spectrum of anthracene are discussed and are related to its absorption and fluorescence spectra. The role of surface effects, defects and impurities are discussed in relation to the fluorescence of anthracene. The method of A.C. detection was unable to resolve the excitation spectrum of anthracene due to the high noise level associated with the method. However, peaks in the ultra-violet region of the hydrogen molecular spectrum were recorded at a modulation frequency of 400 Kc/sec. The noise level is explained and ways of improving the signal to noise ratio of the A.C. detection system are suggested. It is concluded that D.C. detection is a simpler and more direct way of measuring excitation spectra. No modulated signals were detected when the hydrogen discharge was excited at 6·5 Mc/sec. Signals were recorded at modulation frequencies of 400 Kc/sec . The degree of modulation at 400 Kc/sec. increased with decrease in the pressure of the hydrogen discharge.
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- Date Issued: 1963
A theoretical investigation of the effects of solar eclipses on the ionosphere
- Authors: Walker, Anthony David Mortimer
- Date: 1962
- Subjects: Solar eclipses , Ionosphere , Solar activity
- Language: English
- Type: Thesis , MSc , Masters
- Identifier: vital:5550 , http://hdl.handle.net/10962/d1013467
- Description: The behaviour of the ionosphere during a solar eclipse is of great interest because radiation from the sun is the cause of ionization in the upper atmosphere and it is useful to be able to conduct experiments where this radiation is cut off and restored in a known manner. Experimental results, especially those dealing with the F2 layer, have proved puzzling. Cusps which cannot be explained appear on the records obtained from ionosphere sounders and in the F2 region the electron density at a given height shows a maximum after the eclipse where one would expect it simply to rise to a steady value. An attempt is made in this thesis to explain some of the anomalies in terms of tilts in the ionospheric layers and minima of electron density or "valleys" between the ionospheric layers. The problem is attacked theoretically. Part I deals with the theoretical background to ionospheric physics in general and to this problem in particular. Standard methods of dealing with radio propagation in the ionosphere as well as some methods developed by the author are discussed. Part II deals directly with the effects of a solar eclipse on a theoretical ionosphere. Ionograms which would be obtained in the theoretical ionosphere are constructed. These are scaled by standard methods to show where errors may arise . It appears that tilts in the layers have only a small effect. The effect of the valley is, however, extremely important, giving rise to the apparent maximum of electron density in the F2 layer at a given height after the eclipse. This maximum does not in fact exist but arises from an error in the scaling method which ignores the possibility of a valley. Some records taken during the solar eclipse of 25 December, 1954 have been scaled. They support the conclusion reached theoretically.
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- Date Issued: 1962
An investigation of solar radio noise in relation to visible phenomena
- Authors: Poole, Lex Martin Graham
- Date: 1961
- Subjects: Solar radio emission , Radio astronomy -- Instruments
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5536 , http://hdl.handle.net/10962/d1013032
- Description: The work of previous writers on the origin and propagation of solar radio noise, and particularly the correlation with visual events is reviewed, and then the construction of the author's 300 Mc/s receiver described. With a view to the author's project, absorption of electromagnetic radiation in the solar corona is quantitatively discussed, and a method for determining the intensity without absorption of a radio burst is evolved. The main project involves briefly the discovery of any possible relationship between the magnitude of a visual flare and the corrected intensity of an associated radio burst as measured at 125 Mc/s. It is concluded that no definite relation exists, but from this consideration an approximate shape of the instantaneous frequency profile of outburst elements is obtained. An extension of the theory to isolated bursts enables us to predict both this bandshape, and the velocity of an exciting agency moving radially through the corona.
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- Date Issued: 1961
An investigation of the polarization of solar radio noise
- Authors: Verschuur, Gerrit L.,1937-
- Date: 1961
- Subjects: Solar radio emission , Polarimetry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5547 , http://hdl.handle.net/10962/d1013441
- Description: CHAPTER I A description of the sun and the type of radio radiation it emits is given. The relation that exists between this and other events occurring on the sun's surface is studied. CHAPTER II The literature dealing with the origin of solar radio noise is reviewed. CHAPTER III The method of specifying polarized radiation and the effect of a magneto- ionic medium on such radiation is discussed. The possible origin of the polarization of solar radio noise is examined and the literature relating to this and to the observations of polarization of solar noise is reviewed. A short outline of the methods used in measuring polarization is given. CHAPTER IV A detailed outline of the construction of a polarimeter is given together with full circuit diagrams and illustrative photographs. CHAPTER V A brief discussion of the operation of the polarimeter, the results obtained and suggestions for its future operation is given.
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- Date Issued: 1961
An investigation of the profiles of bursts of solar radio noise
- Authors: Wild, Peter Anthony Thornton
- Date: 1960
- Subjects: Solar radio emission , Radio noise , Solar noise storms , Radio astronomy
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5551 , http://hdl.handle.net/10962/d1013504
- Description: [Summary] Chapter I . The general characteristics of solar radiation at metre wavelengths are described, with reference to data published in the literature. A brief description of some aspects of solar physics relevant to the study of solar noise is given, and the literature relating to the correlation of radio effects with solar disturbances is reviewed. Chapter II. A concise description of the apparatus constructed for the continuous recording of the flux density of solar radio noise at a frequency of 300 Mc/s is given, with some mention of difficulties experienced, and how these were overcome. Full circuit diagrams of electronic apparatus, and illustrative photographs, are supplied. Chapter III. The development of theories of the origin and propagation of solar noise radiation is historically reviewed and the success of each theory in explaining or predicting observed phenomena, is assessed. A working model is chosen from among these theories, and reasons for its adoption are given. Chapter IV. Observations made by the author of solar radiation at a frequency of 300 Mc/s are described, together with a description of the objects and methods, of analysis of the records. Chapter V. Phenomena observed by the author are compared with those observed by other workers. It is concluded that storm bursts are caused by transients similar to those producing Type II and Type ITI bursts, and a model for the production of storm bursts is tentatively suggested. Chapter VI. Suggestions for further research, including suggestions for methods of testing the author's conclusions, are made.
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- Date Issued: 1960
An investigation of isolated bursts of solar radio noise
- Authors: Shuter, William Leslie Hazlewood
- Date: 1958
- Subjects: Solar physics -- Research , Solar radio emission
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5539 , http://hdl.handle.net/10962/d1013216
- Description: The literature on isolated bursts and possible mechanisms of origin has been critically reviewed, and observations point to a mechanism involving omission of electromagnetc radiation from plasma oscillations in the solar corona excited by outward travelling disturbances. Solar noise observations on 125 Mc./s. recorded at Rhodes University during the period November 26 1957 - February 6 1958 have been analysed by the author for isolated bursts, and these observations show the same general features reported by previous investigators. In interpretation of these records particular attention has been devoted to two aspects of isolated bursts; namely the preponderance on single frequency records of double-humped bursts, and the shape of isolated burst profiles. The authors suggests that a probable explanation of double-humped bursts observed on any frequency f is that the first hump represents omission at or near the level of zero refractive index for f radiation, and that the second hump corresponds to harmonic omission at the f/2 level. Source velocities may be calculated from the time delay between the peaks and an average value of 2 x 10⁴ km./sec. was obtained from an analysis of 21 double-humped bursts. This value is in very good agreement with that deduced by Wild (1950b) from the rate of frequency drift of peak intensity of isolated bursts. Simple isolated bursts had decay profiles which are approximatley exponential in shape, and this is usually interpreted in terms of the natural decay of plasma oscillations in the medium of origin. The author has verified that the exponential function is a good fit to the observed decay profiles, but shows that a relation of the form I - ¹/n (superscript) ⋉ t (where I is intensity and t is time) fits just as well. An alternative model is suggested which would lead to an exponential-like decay profile which is not determined by the natural decay of plasma oscillations. The work concludes with some suggestions for further research.
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- Date Issued: 1958
Photofluorescence decay times of organic phosphors
- Authors: Hamilton, T D S
- Date: 1957
- Subjects: Fluorescence , Phosphorescence
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5525 , http://hdl.handle.net/10962/d1012136 , Fluorescence , Phosphorescence
- Description: The absorption and emission of energy is a fundamental property of any atomic system.When the emission occurs in the visible or near visible region the phenomenon is usually referred to as luminescence or fluorescence. This must be distinguished from thermal radiation as it does not follow Kirchoff's law.
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- Date Issued: 1957
The response of pure organic crystals to ionising radiations
- Authors: King, J W
- Date: 1953
- Subjects: Inorganic scintillators , Crystals
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5529 , http://hdl.handle.net/10962/d1012641 , Inorganic scintillators , Crystals
- Description: The introduction contains introductory remarks on scintillation counters together with a brief description of the exciton theory believed to be the means of primary energy migration within organic crystals. Part I contains a review of the data published on the reletive responses of different organic crystals and the attempted correlations of these results with the molecular structures of the different phosphors. From data which may be accepted as being both reliable and suitable for comparison it is concluded that theories involving correlations between phosphor efficiencies and molecular structures may be tested only if the efficiency data has (i) been extrapolated to give results for crystals of very small thickness and {ii) been obtained at very low temperatures. Part II contains accurate calculations based on the exciton theory proposed by Birks (1951 ) to account for the response of crystals to different types of ionising radiations. Satisfactory agreement is obta1ned with all the avalable experimental data in the literature. In part III an account is given of the response of organic crystals observed by the author for low-energy ⋉particles, and of the similar behaviour found by Taylor et al, (1951 ) for low-energy electrons. A possible extension of the theory described in part II, allowing for the escape of excitons through the crystal surface is given accounting for this behaviour. An exciton mean free path in anthracene, terphenyl and stilbene of about 3 - 7/u is obtained. Results were obtained with strong ⋉-particle sources which could not be explained. in terms ot normal response of the phosphor used. This effect was inventigatea as described in part IV, and it is shown that photons are produced in air, glass and quartz when these materials are irradiated by ⋉particles. This luminescence was probably responsible for the "scintillations" which Richards and Cole (1951) have ascribed to thin films of various materials. Problems requiring further investigation are indicated.
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- Date Issued: 1953
A study of the E region of the ionosphere
- Authors: Barnard, A J
- Date: 1950
- Subjects: Ionosphere -- Research
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5549 , http://hdl.handle.net/10962/d1013464
- Description: After a brief historical introduction, the apparatus used in the investigation of the ionosphere in Grahamstown, is described with special reference to the recording equipment, which consists essentially of a camera focussed on the screen of a C.R.O. with z-axis deflection. The equations of the magneto-ionic theory are quoted. The basic formulae of the theories of layer formation in an isothermal (Chapman's),and linear temperature gradient (Gledhill and Szendrei) atmosphere are also quoted.
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- Date Issued: 1950