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Unit 21 learning aim A and B
- Institution
- PEARSON (PEARSON)
I received a distinction for this unit so use this to write up your own :)p.s this isn't the distinction task look on my page to find it titled ...Distinction.
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Unit 21 Medical physics,P1:
Atom
Introduction Figure 1
An atom is the minutest particle of a chemical element that can exist. It has a
central nucleus (which contains the proton and neutron) that is surrounded by
electrons which are organized in shells. It also contains subatomic particles
which are protons and neutrons inside the nucleus. The protons are positive,
neutrons are neutral and electrons have a negative charge. The mass of an
electron is minute in comparison to a proton or a neutron. As the nucleus
contains protons and neutrons, most of the mass of an atom is concentrated in Figure 2
its nucleus.
The Electromagnetic Spectrum
The EM spectrum is a series of waves with various frequencies and lengths; it is
organized in order of size starting from the longest to the shortest wavelength. The
arrangement of the em spectrum is: Radio waves, Microwaves, Infrared, Visible
light, Ultra violet, X-rays and Gamma rays.
The length of the waves rises as you go more towards the right side if the em
spectrum (radio waves being longer and gamma rays being shorer). The lower the
frequency the longer the wavelength is which means it can only deliver minute
amount of data however, high frequencies that have short waves are able to deliver
more information. Radiowaves and microwaves are mostly used for communication
purposes due to the long distances they can go. Infrared is adopted in night vision
and security and ultraviolet light is operated in tanning beds as well as
photography.
,Ionizing Radiation Figure 3
Ionising radiation is radiation that carries enough energy to remove electrons from atoms or
molecules therefore ionizing them. It is formed of ions, atoms or subatomic particles. They
can cause harm to the cells however they will mend themselves. It could also possibly cause
cells to mutate themselves which means there's a risk of the cells not being able to
reproduce correctly. Examples of ionising radiation are: x-rays, gamma rays, alpha and beta
particles.
Non-Ionising radiation
Non ionising radiation is any form of EM radiation that doesn't transmit sufficient energy to
ionise atoms or molecules. As it is reliant on the energy and disclosure time, non-ionising
radiation can make localised heating, or photochemical reactions can happen with probable
permanent damage. Disclosure should therefore be reduced. Examples of non-ionizing
radiation are: visible light, infrared, microwave, radio waves etc.
Radioactive Decay
Radioactive decay is the method by which an unstable atomic nucleus loses energy by Figure 4
emitting radiation. There are three types of radioactive decay: alpha, beta and gamma decay.
In an alpha decay the weak nucleus discharges two protons and two neutrons which is the
same as a helium nucleus. In a beta decay electrons are emitted from the nucleus which
happens in atoms where there are more neutrons than protons (the additional neutron is
halved into a proton and electron, the protons stays in the nucleus whereas the electron is
discharged). Gamma decay happens next to alpha or beta decay as the nucleus is slightly
unstable. In gamma decay no atoms are destroyed instead photons are emitted.
Overall, alpha atoms are highly ionising while beta is less ionising than alpha making gamma
rays the least ionising.
, Figure 9
P1-Ultrasounds
An ultrasound scan, sometimes referred to a sonogram, is a procedure that uses high-frequency sound waves
(can go higher than 20,000 Hz) to make an image of part of the inside of the body. Sound waves are longitudinal
which means they can pass through solids, liquids and gases. They are a form on non-ionising imaging and can
be used in industrial area as well as medical methods for instance: looking at structures of the body that are not
encircled by bone, finding depths of water in the oceans and finding cracks in metal. There are two types of
ultrasounds which are therapeutic and diagnosis. As there is no risk of cancer and mutation to cells they are
usually used instead of CT scans and X-Rays.
Production:
- The vibrating source (piezoelectric transducer) is in contact with the tissue, which makes it vibrate.
- The vibrations in the area of tissue next to the transducer is transferred on to the adjacent tissue. This process carries on
- The time in which the tissue structures vibrate back and forth is the frequency of the sound whereas the time in which th
pass through the tissue is the velocity of the sound.
- The sound in a lot of diagnostic ultrasound systems is diffused in pulses instead of a continuous stream of vibrations. The
kept within a relatively minute volume of the material; this volume of vibrating material is known as the ultrasound pulse
- As the vibrations are moved from one area of material to another, the ultrasound pulse (not the material), moves far from
- As the longitudinal vibrations move through a area of tissue, rotating changes in pressure are made.
- During one part of the vibration cycle the tissue will be squashed with an increased pressure. During the other part of th
a decline in pressure and an action of rarefaction. Figure 33
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