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The east-west asymmetry of cosmic rays in high latitudes.


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Burbury, Douglas William Petrie 1951 , 'The east-west asymmetry of cosmic rays in high latitudes.', PhD thesis, University of Tasmania.

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The experimental work described in this thesis
was carried out with the subject of obtaining information
on the east-west asymmetry of cosmic rays in latitudes
above the so called knee of the latitude intensity
variation of the total cosmic ray intensity. As is
explained in the Introduction, the variation of
intensity with latitude and the east-west asymmetry
observed between the geomagnetic equator and the
latitude . of.the knee (about. 45 °geomagnetic) can be
explained in terms of the effect on the primary radiation
of the earth's magnetic field. At higher latitudes
where little or no variation of the intensity with
latitude has been found, the east-west asymmetry
should vanish according to this theory. A small
asymmetry has however been found by various workers,
notably T.H. Johnson and F.G.P. Seidl, in latitudes
above the knee. Johnson (1941) has given a theory to
account for this as an effect produced by the deflection .
of secondary cosmic ray particles in the earth's field.
The values of the asymmetry calculated by Johnson
for various zenith angles were compared with results
obtained at 49° and 54° north geomagnetic latitude. Owing to the large probable errors of the experimental
results, no more than a very general conclusion could
be drawn from the comparison. The geomagnetic latitude
of Hobart, 51.7°S, made it a suitable place to obtain
results to supplement those of Seidl and Johnson,
and the Hobart experiments were planned with the aim
of improving the statistical precision of the results
to a point where they could be used as the basis of
a critical test of Johnson's theory. In the later
sections of this thesis the theory is discussed in
some detail. The values of the asymmetry which might
be expected have been recalculated, using more recent
data than that available to Johnson, graphical and
-numerical methods being substituted for analytical
methods in some parts of the calculations in order
to use empirical data directly.
It is important to establish as definitely
as possible that the deflection of secondary cosmic
rays between the top of the atmosphere where they
are produced and sea level can lead to an asymmetry
because of the apparent contradiction which the
asymmetry observed in high latitudes presents to the
general theory which has been found to explain the
geomagnetic effects in a satisfactory manner. BY
showing that Johnson's, or a similar theory can
adequately explain this phenomenon, the contradiction can be removed.
The history of the experimental work on this
problem is as follows. In 1946, Dr. A.G. Fenton
commenced work on the construction ofan automatic
apparatus using a single geiger counter telescope
pointing east and west alternately to measure the
asymmetry. The author assisted with this work,
and in 1947 when Dr. Fenton was absent on leave from
the laboratory, completed the apparatus and operated it
successfully to obtain results which were published
in the Physical Review (Vol. 74, 589, 1948). While
this setup was in operation it was decided to construct
an apparatus using two geiger counter telescopes instead
of one. The advantages of such an arrangement are
discussed in the section in which this apparatus is
described. The design and operation of this setup
was almost entirely the work of the author. It was
operated from the end of June 1948 until the
beginning of August, 1949.
At the end of 1948 the Australian National
Antarctic Research Expedition became interested in the
.investigation of the asymmetry and made a grant of
money to enable Dr. Fenton's brother, Mr. K.B. Fenton,
to extend the work to geomagnetic latitude 60.7°S by
operating an apparatus Similar to the Hobart one on
Macquarie Island in 1950 and possibly 1951. Problems incident to the operation of apparatus
remote from the facilities available in the laboratory
made the construction of this apparatus a project of
considerable magniitude, and it was accordingly
shared between Dr. Fenton, his brother, and the author.
Dr. Fenton Who had worked on the properties of geiger
counters in Birmingham undertook to construct the
counters required,. while his brother took responsibility
for the design and construction of suitable recording
circuits. The contributions of the author to this work
are described in Part II, and included the design of
an automatic 35mm. camera to record the results,
the modification of a turntable previously used in
a Predictor unit to make it suitable for mounting
of the apparatus, and the design of control gear to
make the setup automatic in operation. The construction
of this apparatus was successfully completed in time
for it to be shipped to Macquarie Island in April, 1950.
Between April and June, 1950, the Hobart
apparatus was modified to include several improvements.
The most important of these wee the fitting of larger
trays of geiger counters to increase the counting rates,
which was possible because of the improved supply of
counters available at that time. The modifications were
completed by the tithe the Macquarie Island gear was
ready for use, and the two sets were put into operation
on parallel schedules at the end of June, 1950.

Item Type: Thesis - PhD
Authors/Creators:Burbury, Douglas William Petrie
Keywords: Cosmic rays
Copyright Holders: The Author
Copyright Information:

Copyright 1951 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1952

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