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12 Cards in this Set
- Front
- Back
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Production of X-Rays in an X-Ray Tube |
Low voltage (6V) supplied to filament to heat it up
Thermionic emission of electrons from filament
Electrons emitted to high vacuum - free passage
EHT to accelerate electrons to anode (+ve) • Anode made from target metal (high melting point) (Tungsten) • Target = small so sharp shadow is produced
X-Ray photons produced when electrons = decelerated by hitting anode • They travel out through window in tube • Rest of tube = lined with lead • Stop X-Rays travelling out in other directions |
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Minimum Wavelength of an X-Ray (λ) |
λ = hc ÷ eV |
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Length of X-Rays |
10⁻⁸ - 10⁻¹³ m |
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X-Ray Attenuation - Simple Scatter |
X-Ray photon is scattered elastically by an electron (E = 1-20 keV) |
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X-Ray Attenuation - Photoelectric Effect |
Electron is released from the atom (E < 100 keV) |
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X-Ray Attenuation - Compton Effect |
X-Ray photon is scattered with less energy and electron is released (E = 0.5-5.0 MeV) |
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X-Ray Attenuation - Pair Production |
Electron - Positron pair is produced (E ≥ 1.02 MeV) |
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Equation for X-Ray Attenuation |
I = I₀e⁻μˣ where: I = Transmitted intensity I₀ = Initial intensity μ= Attenuation/Absorption coefficient (m⁻¹) x = Thickness of substance (m) Bigger μ = Better at absorbing X-Rays |
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Contrast Media |
Soft tissues have low attenuation coefficients so contrast media are used to improve the visibility of their internal structures in X-Ray images Barium and Iodine have high attenuation coefficients so fewer X-Ray photons pass through allowing the tissue to appear Iodine is normally used in liquids (tracking blood flow) Barium is normally used in the digestive system (viewing the intestines) |
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Therapeutic Use of X-Rays |
Specialised X-Ray machines (linacs) are used to create high energy X-Ray photons Used to kill cancerous cells through Compton scattering and pair production |
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Advantages of X-Rays |
Quick (Fraction of a second) Equipment is mobile (Can be taken to a bed) Low X-Ray Dose (Compared to CAT Scans) |
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Disadvantages of X-Rays |
Creates a shadow image with organs superimposed |
