TRANSMISSION AND ABSORPTION MEASUREMENTS OF HIGH ENERGY ELECTRONS WITH METALLIC AND INSULATING FOILS.
TRANSMISSION AND ABSORPTION MEASUREMENTS OF HIGH ENERGY ELECTRONS WITH METALLIC AND INSULATING FOILS.
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Date
2014-05-14
Authors
Benson, Nwabueze Chukuomeka
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Abstract
The possible dependence of the extrapolated ranges of electrons
on the detector characteristics has been investigated by two methods.
These experiments were performed under well standardised geometrical
conditions, employing electron beams (0.25 - 0.75 MeV) derived from a
Van de Graaff electrostatic generator. The possible effects of poor
geometry and small bias voltages on range values have also been
investigated, but the results show that these effects could be kept
very small in normal transmission measurements. The range values
obtained in five metals (Be, Al, cu Ag and Au) and in four dielectrics
(glass, mica, sulphur and polystyrene)by direct curre.it collection
method and in Al, Ag and mica by an ionisation method, show that the
latter method yields larger range values.
A comparison with other results showed that the range value6
obtained with the Geiger counter are also greater than those obtained
by the current collection method. The ionisation-in- depth results
in Al showed good agreement with the other results, aid with Spencer's
theory for equivalent source geometry. A universal transmission curve
was obtained for each element using the true range vaLues calculated
from the Bethe-Bloch stopping power formula, and its Intercept was
found to be a smooth function of the atomic number for both metals
and insulators,
Electron bombardment conductivity has been studied primarily
in sulphur and in selenium for comparison. Large current gains were
observed in sulphur in confirmation of von Hippel's theory of the
conductivity of the elements of Group VIb of the periodic table. The
single crystals of sulphur showed as much bombardmenl conductivity as
selenium, but much greater conductivity than the polycrystalline
specimen, as was noted by Joffe(1928)and as would be expected for a
more perfect crystal lattice. The dependierce of electron bombardment
conductivity and the current distribution in bombarded dielectrics on
the depth of penetration has been studied and the effects of spacecharge
on these phenomena investigated and discussed,
Description
A Thesis
submitted to The University of Leicester
by
Benson Nwabueze Chukuomeka Agu, B.Sc.
for the degree of
Doctor of Philosophy
Keywords
TRANSMISSION,, ABSORPTION,, MEASUREMENTS,, ENERGY ELECTRONS,, METALLIC,, INSULATING FOILS