Spectra of scattered radiation at points off the beam axis
Date
1959-07
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Publisher
ORCID
Type
Degree Level
Masters
Abstract
In radiological physics, a knowledge of the spectral distribution
or radiation reaching a point is very important. Although the dose
gives the amount of radiation at the point, it is the spectral distribution
which determines the effects, for instance, the energy absorbed
by the irradiated medium.
In an irradiated medium radiation reaching a point consists of
primary and scattered radiation. The scattered radiation becomes more
important as the depth is increased.
In this investigation, the spectral distributions of scattered
radiation at 1.47 cm inside, at 1.88 cm outside the boundary of the field
and at the central axis were measured with a scintillation spectrometer
for two qualities of X-rays, 280 KVP, HVL of 2.5 mm Cu and 140 KVP, HVL
of 1.45 mm Al. A circular beam of 100 cm2 at FSD of 60 cm was used.
Measurements were carried out at 5 cm depth for 280 KVP and 2 cm depth
for 140 KVP.
It was found that for 280 KVP radiation, the shapes of the integrated
spectra inside the field, outside the field and at the centre are nearly
the same. However, the dose received at 1.47 cm inside is 73% of that at
the centre and 1.88 cm outside is 37% of that at the centre. It should
be pointed out that at the centre, the scattered radiation contributes
about half the total dose.
For 140 KVP radiation, the peak of the scattered spectrum becomes
broader as the distance from the centre is increased. The dose received at 1.47 cm inside is 83% or that at the centre and 1.88 cm outside
is 25% of that at the centre. For the central point the scattered
radiation accounts for approximately 50% of the total dose received.
Comparisons were made with doses calculated by a method suggested
by Clarkson together with the depth dose data. Reasonable agreement
was found.
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Degree
Master of Science (M.Sc.)
Department
Physics
Program
Physics