Medical physics

What is the frequency of an x-ray?

3X10^16 Hz - 3X10^19 Hz

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What is the wavelength of an x-ray?

1X10^-8 - 1X10^-11

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How does an X-ray tube work?

A heater excites the electrons to move out from the atom. A Tungsten anode will accelerate these. (The electrons accelerate towards it).The electrons are then emitted as x-ray photons.

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Why does the Tungsten anode have a special shape?

It enables the photons to be emitted in the required direction.

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Why is the tube incased in lead?

For safety as the x-rays cannot pass through.

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What is pair production?

A procces where an X-ray photon produces a an electron-positron pair

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Describe the photoelectric effect

In the photoelectric effect, a single photon interacts with a single electron at the surface of a metal. In this, energy is conserved. In Einstein equation, hf is the energy of the photon and 1/2mv^2 is the max Ke of the electron.

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What is the Compton effect?

scattering An interaction between an x-ray photon and an electron in which the photon is scattered with a longer wavelength.

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Using logarithms solve: 8^(4-x)=33

x=2.319

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Using logarithms solve: e^(7-x) +7=1009

x=0.09....

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What is meant by the attenuation of x-rays?

Attenuation is the reduction of the intensity of an x-ray beam as it traverses matter. The reduction may be caused by absorption or by deflection (scatter) of photons from the beam

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For medical x-rays would it be more beneficial to use x-rays with a high or low energy?

Lower- biggest difference between attenuation of materials

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How do CAT Scans work?

X-ray tube and detectors are rotated around the body. It is a thin fan shaped beam of x-ray photons. The detectors send the intensities detected to a computer which forms an image of a slice. It is then moved down the body for another slice.

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What are the advantages of CAT Scans over normal x-rays?

3D images are produced in CAT scans. Also, CAT scans can see soft tissues.

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What is human hearing range?

20Hz - 20KHz

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What is ultrasound?

Ultrasound is sound too high for a human to hear so is greater than 20KHz.

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How does the wavelength effect the image produced?

A smaller wavelength will produce a clearer image with more detail. Ultrasounds hove a small wavelength.

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What is a B-scan?

Is a brightness scan. Produces brightness levels based on echo strengths.

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What is an A-scan?

Boundary echos are detected.

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What will be the result of a greater difference in acoustic impedance be to the rays?

More rays will be reflected

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What is the Piezoelectric effect?

Piezoelectric crystals produce ultrasound. This is done using an alternating current to create fast vibrations are made. This is called a Piezoelectric transducer- creates patterns of echos.

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What is Doppler imaging?

The Doppler effect states that when a wave is reflected off a moving medium the frequency of the wave changes.By measuring the change in frequency of reflected waves Doppler scans can be used to scan blood vessels & flow of blood.

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Medical physics

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