BTEC Applied Science Unit 4, Assignment D (FULL ASSIGNMENT)
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BTEC
PEARSON (PEARSON)
Applied Science 2016 NQF
Unit 21 - Medical Physics Applications
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What is ionising radiation?
Ionising radiation is radiation from electromagnetic waves containing sufficient energy to break
chemical bonds, thus producing charged ions in the materials they pass through.
Two examples of ionising radiation techniques which are used to provide medical
diagnosis/treatment are X-rays and Gamma Ray imaging
P3. The production of X-rays
X-rays are produced from very high-speed electrons which stop suddenly when they hit a metal
target plate. A filament becomes heated due to the flow of electrical current. The electrons
(which have a negative charge) are emitted by thermionic emission and accelerate towards the
anode (which is kept cool using circulating oil or water). This gives a positive charge of up to
100kV. The X-ray is produced when the electrons high speed increases their kinetic energy;
enabling them to hit the metal target (generally tungsten on a copper block). From this, a very
small percentage of the electron kinetic energy is transformed into X-rays, with the remaining
99.5 percent transformed into heat. The X-ray then passes through a small window in the lead
shielding.
P3. The principles of X-rays
The intensity, quality and wavelength of X-ray beams affects the point of penetration. The most
dense parts of the body will absorb the X-ray beams well i.e. bones, which are dense, will be
more apparent on the X-ray whereas tissues, which are less dense, will not absorb X-rays as
well and will be mummy to ch darker and less visible on X-rays.
X-rays are part of the electromagnetic spectrum, meaning they spread out as they travel. The
further the distance travelled by the X-ray, the lower the intensity will be of the X-ray. This is an
example of an inverse square relationship where the intensity of the X-ray drops by one quarter
of its original value as the distance travelled is doubled.
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