1
1.0 Introduction
This report investigates radioactivity and half-life, the production of X-rays and the operation of X-ray machinery, and the production of ultrasound waves and how they are used in the commercial industry. A separate sub-chapter has been included that defines acoustic impedance that makes ultrasound technology possible.
2.0 Task 1: Radioactivity and Half-life
This chapter will discuss Radioactivity, property exhibited by certain types of matter of emitting energy and subatomic particles spontaneously. It is, in essence, an attribute of individual atomic nuclei. Half life is simply when an atom is half way through its predicted life. Details are provided in the following sub chapters.
2.1 Radioactivity and atomic structure
Radioactivity can be given of as Ionising radiation is any type of particle or electromagnetic wave that carries enough energy to ionise or remove electrons from an atom. There are two types of electromagnetic waves that can ionise atoms: X-rays and gamma-rays, and sometimes they have the same energy. Gamma radiation is produced by interactions within the nucleus, while X-rays are produced by electrons. Atomic structure is Atoms are composed of three types of particles: protons, neutrons, and electron. Protons and neutrons are responsible for most of the atomic mass e.g in a person while only 1 oz. is electrons. The mass of an electron is very small (9.108 X 10-28 grams). (1) (2)
2.2 Random nature of decay and half-life
The alpha particle is composed of two protons and two neutrons, or a helium nucleus and alpha decay is where a nucleus ejects an alpha particle which is identical to an ionised helium nucleus Beta decay happens when a neutron within an atom’s nucleus transforms into a proton and an electron and an antineutrino are ejected out of the nucleus of an atom. For a beta plus decay a proton transforms to a neutron and a positron (similar to an electron but with a positive charge) and a neutrino are ejected out of the nucleus. Gamma decay is types of radioactivity in which some unstable atomic nuclei dissipate excess energy by a spontaneous electromagnetic process. In the most common form of gamma decay, known as gamma emission Half-life (symbol t1?2) is the time required for a quantity to reduce to half its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo, or how long stable atoms survive, radioactive decay. (3)
2.3 Summary
Radioactivity is the process in which unstable atomic nuclei spontaneously decompose to form nuclei with a higher stability by the release of energetic sub atomic particles. Atoms are made up of protons, neutrons and electrons each with their own properties. The Atomic structures of an atom is broken up into three categories this is Protons have a positive (+) charge Electrons have a negative (-) charge Neutrons has no charge (Neutral). Half life is the term used to describe when an atom has reached one half way through its life
3.0 Task 2: X-rays
X-rays are a form of electromagnetic radiation that is used in medicine to view body part in detail without cutting the human body open this form of treatment is very useful in the medical industry but this is limited treatment because it is very expensive it is also in limited access because only major hospitals have them but if a hospital is lucky enough to actually own one then a patient can only have a limited number of x rays a year because the radiation that patients get exposed to can be lethal in certain doses. The following sub chapters includes information about this process.
3.1 The production of X-rays
An X-ray machine consists of an evacuated tube in which two electrodes are found. The negative electrode (also called the cathode) is a wire filament that emits electrons when heated. This process is called thermionic emission and the wire filament is called an ‘electron gun’X-rays are produced due to sudden deceleration of fast-moving electrons when they collide and interact with the target anode. In this process of deceleration, more than 99% of the electron energy is converted into heat and less than 1% of energy is converted into x-rays. The x-rays that bounce of in another direction are absorbed by the lead housing around the vacuum itself this is to prevent any radiation from escaping the housing because although its only a small dosage of radiation it can still be harmful (4) (5)
Ref: http://www.cyberphysics.co.uk/graphics/diagrams/medical/XRay_Tube.png
Ref:https://miac.unibas.ch/PMI/01-BasicsOfXray-media/figs/Characteristic_Spectrum.png
Ref : https://www.heritagedaily.com/wp-content/uploads/2016/03/xray1.jpg
3.2 Analyse the effect of the operation and design
By launching a high energy electron at a target, when the target approaches a nucleus of an atom, it will be attracted to it. The nucleus won’t move much because it is so much larger than the electron however an x- ray beam consists of a spectrum (a disruption) of photon energies. The rate of the energy that is delivered by the beam is determined by a beam of photons of each energy although Typically in a filament driven with a fixed current, and the total emission counts will be directly proportional to the filament current. A high voltage (usually from 10kV to 100kV, depending on the application) is applied between the cathode and the anode. Electrons are ejected from the filament by thermionic emission, and then accelerated by the high voltage potential over to the anode. The emitted x-ray energies will have a maximum cut-off energy equal to the applied voltage times the charge of an electron — i.e. apply 30 kilovolts from the cathode to the anode and the highest energy will be 30 kilo-electron volts. (6)
3.3 Summary
In conclusion x-rays are electromagnetic waves that can used in the medical industry, as well as other industries they allow use to see within the human body without having to use any form of intrusive surgery. They paint an accurate picture that are used by processionals to determine any problems/issues that may arise within the body of the patient that. However the amounts of exposures per person are limited because in moderate dosages the x-rays can cause damage to the human body.
4.0 Task 3: Ultrasound
Ultrasound technology is used in all manner of equipment. It uses sound waves that are reflected, that in turn creates an image. This chapter describes how an ultrasound wave is produced with an example of the equipment in use that uses this technology. The operation and analysis of ultrasound waves is also included showing in principle how acoustic impedance is utilised.
4.1 The production of Ultrasound
Ultrasound relies on high frequency sounds to image the body and diagnose patients. Ultrasounds are therefore longitudinal waves which cause particles back and forth and produce a series of compressions. Ultrasound uses high frequency sounds that are higher than the human ear can hear. ie. 20 000 Hz. Ultrasound can’t detect objects that are smaller than its wavelength and therefore higher frequencies of ultrasound produce better resolution. On the other hand, higher frequencies of ultrasound have short wavelengths and are absorbed easily and therefore are not as penetrating. For this reason high frequencies are used for scanning areas of the body close to the surface and low frequencies are used for areas that are deeper down in the body thus because of this x-rays are used to detects objects within the human body such as tumours and cancer because x-rays can see straight through the human body and give a more precise image at longer ranges. (7)
Ref:http://ichef.bbci.co.uk/news/1024/cpsprodpb/A973/production/_84197334_thinkstockphotos-178438513.jpg
4.2 Analyse the effect of Ultrasound
Ultrasound is a medical diagnostic imaging technique in which very high frequency sound is aimed into the body. This technique is used to visualize the structures of certain parts of the body including tendons, muscles, joints, vessels and internal organs. The ultrasound scanner sends pulses into a patient’s body through a transducer and the return echoes are processed by a computer to display real time image on a monitor (7)
4.3 Acoustic impedance
The natural or inherit property in material that determines how sound travel through it. Z=pv ( p is density and v is sound velocity). Ultrasonic waves are reflected at boundaries where there is a difference in acoustic impedances (Z) of the materials on each side of the boundary. This difference in Z is commonly referred to as the impedance mismatch. The greater the impedance mismatch, the greater the percentage of energy that will be reflected at the interface or boundary between one medium and another (8)
Acoustic impedance (Z) is a physical property of tissue. It describes how much resistance a ultrasound beam encounters as it passes through a tissue.
The acoustic impedance depends on, the density of the tissue (d, in kg/m3) and the speed of the sound wave (c, in m/s) and they are related by:
Z = d x c
So, if the density of a tissue increases, impedance increases. Similarly, but less intuitively, if the speed of sound increases, then impedance also increases.
The effect of acoustic impedance in medical ultrasound becomes noticeable at interfaces between different tissue types. The ability of an ultrasound wave to transfer from one tissue type to another depends on the difference in impedance of the two tissues. If the difference is large, then the sound is reflected. When an ultrasound beam passes through muscle tissue and encounters bone, it reflects off of it due to the difference in density between the tissues. The amount of reflection that occurs in a perpendicular direction is expressed by:
Reflection fraction = (Z2 – Z1) / (Z2 + Z1)2
Where Z1 and Z2 represent the impedance in tissue 1 and tissue 2, respectively.
Ref:http://www.cyberphysics.co.uk/graphics/diagrams/medical/acousticImpedance.png
Examples of impedance for bodily tissues (in kg/(m2s)):
• air 0.0004 × 106
• lung 0.18 × 106
• fat 1.34 × 106
• water 1.48 × 106
• kidney 1.63 × 106
• blood 1.65 × 106
• liver 1.65 × 106
• muscle 1.71 × 106
• bone 7.8 × 106
Test workings:
Reflection fraction = (Z2 – Z1) / (Z2 + Z1)2
Fat – liver example
Rf = (1.65 – 1.34) / (1.65 + 1.34) 2 = 0.31 / 2.992 = 0.01 = 1%
Bone – muscle example
Rf = (7.8 – 1.71) / (7.8 + 1.71)2 = 6.09 / 9.51 2 = 0.64 = 41%
Using these values with the equation above, you would see that less than 1% of sound is reflected at a fat – liver interface as apposed to the bone – muscle interface that records 41%. If the sound wave is not perpendicular to a surface, some of the sound wave will be reflected away from the transducer (9)
4.4 Summary
There is very little danger in an ultrasound operation however the image received and it will be hard to make out but for an ultrasound scan this is perfect because if an x-ray operation is conducted for a scan such as this one it may cause damaging effects to the baby and an x-ray is very expensive compared to a standard ultrasound scan. Also the depth in which the scan is required is fine for ultrasound where as x-rays would show a slightly clearer image but it may damage the baby.
5.0 Discussion
Both X-ray equipment and ultrasound equipment can be used to explore the contents of a human being or other objects that contain different type of materials. They both rely on a reflected wave. Clever electronics record this reflected data and turn it into useful information, such as an image of what the equipment is focused on. This technology is used in many places such as hospitals, airports, etc.
6.0 Conclusion
The following table shows the differences between x-rays and ultrasound equipment from the research conducted.
X-ray Ultrasound
Can be dangerous Less harmful
Detailed image Lesser quality image
Larger, very expensive equipment Smaller, less expensive, more portable
Wave travels long distance Wave travels short distance
Needs acoustic impedance to work
Bibliography
Foale S, Hocking S, Llewellyn R, Musa I, Patrick E, Rhodes P and Sorensen J –
BTEC Level 3 in Applied Science, Student Book, (Pearson, 2010) ISBN 9781846906800
References
(1)http://www.johnbright.uk/depts/science/Content/Revision_Notes/Y11/Physics/Physics%20-%20Radioactivity.pdf
(2)http://www.physicscentral.com/explore/action/radiationandhumans.cfm
(3)http://www.johnbright.uk/depts/science/Content/Revision_Notes/Y11/Physics/Physics%20-%20Radioactivity.pdf
(4)http://www.bbc.co.uk/schools/gcsebitesize/science/triple_edexcel/xrays_ecgs/xrays/revision/3/
(5)http://www.johnbright.uk/depts/science/Content/Revision_Notes/Y11/Physics/Physics%20-%20Radioactivity.pdf
(6)https://www.quora.com/What-are-the-factors-that-affect-the-design-of-or-the-operation-of-the-X-Ray-tube
(7)http://www.genesis.net.au/~ajs/projects/medical_physics/ultrasound/
(8)http://www.physics.iitm.ac.in/~ph5060/manuals/Ultrasonics.pdf
(9)https://radiopaedia.org/articles/acoustic-impedance
