24.2. Production and use of X-rays
A subsection of Physics, 9702, through 24. Medical physics
Listing 10 of 77 questions
12 The signal-to-noise ratio in an optic fibre must not fall below 24 dB. The average noise power in the fibre is 5.6 × 10–19 W. Calculate the minimum effective signal power in the optic fibre. power = W The fibre has an attenuation per unit length of 1.9 dB km–1. Calculate the maximum uninterrupted length of fibre for an input signal of power 3.5 mW. length = km Suggest why infra-red radiation, rather than ultraviolet radiation, is used for long-distance communication using optic fibres.
9702_s11_qp_43
THEORY
2011
Paper 4, Variant 3
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11 High-speed electrons are incident on a metal target. The spectrum of the emitted X-ray radiation is shown in . intensity wavelength Explain why there is a continuous distribution of wavelengths, there is a sharp cut-off at short wavelength. State what is meant by the hardness of an X-ray beam, how hardness is controlled. Suggest why, when producing an X-ray image, long-wavelength X-ray radiation poses a greater hazard to health than short-wavelength radiation. Suggest how this hazard is minimised.
9702_s12_qp_41
THEORY
2012
Paper 4, Variant 1
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10 An aluminium block is placed near to a small source of X-ray radiation, as shown in . A B aluminium block X-ray source X-rays from the source are detected at point A and at point B. State two reasons why the intensity of the X-ray beam at point B is not as great as the intensity at point A. 1. 2. A cross-section through a model of a finger is shown in . 2.4 cm 1.1 cm bone soft tissue D B C A The thickness of the model is 2.4 cm and that of the bone in the model is 1.1 cm. Parallel beams of X-rays are incident on the model in the directions AB and CD, as shown in . Data for the linear attenuation coefficient μ for the bone and the soft tissue in the model are given in . μ / cm–1 bone soft tissue 3.00 0.27 Calculate the ratio intensity of X-ray beam incident on the model intensity of X-ray beam emergent from the model for the beam AB, ratio = the beam CD. ratio = Use your answers in to suggest why, for this model, an X-ray image with good contrast may be obtained.
9702_s12_qp_42
THEORY
2012
Paper 4, Variant 2
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11 High-speed electrons are incident on a metal target. The spectrum of the emitted X-ray radiation is shown in . intensity wavelength Explain why there is a continuous distribution of wavelengths, there is a sharp cut-off at short wavelength. State what is meant by the hardness of an X-ray beam, how hardness is controlled. Suggest why, when producing an X-ray image, long-wavelength X-ray radiation poses a greater hazard to health than short-wavelength radiation. Suggest how this hazard is minimised.
9702_s12_qp_43
THEORY
2012
Paper 4, Variant 3
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10 Distinguish between sharpness and contrast in X-ray imaging. sharpness: contrast: State two causes of loss of sharpness of an X-ray image. 1. 2. Data for the linear attenuation coefficient μ of X-ray photons are given in . μ / cm–1 bone muscle 2.85 0.95 A parallel beam of X-rays is incident, separately, on a thickness of 3.5 cm of bone and on a muscle of thickness 8.0 cm. Calculate the ratio intensity of X-ray beam transmitted through bone intensity of X-ray beam transmitted through muscle . ratio = Use your answer in to suggest whether an X-ray image of the bone and muscle would show good or poor contrast.
9702_s13_qp_41
THEORY
2013
Paper 4, Variant 1
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12 An optic fibre is used for the transmission of digital telephone signals. The power input to the optic fibre is 9.8 mW. The effective noise level in the receiver circuit is 0.36 μW, as illustrated in . 9.8 mW receiver circuit, noise 0.36 +W optic fibre 85 km input circuit The signal-to-noise ratio at the receiver must not fall below 28 dB. For this transmission without any repeater amplifiers, the maximum length of the optic fibre is 85 km. Calculate the minimum input signal power to the receiver. power = W Use your answer in to calculate the attenuation in the fibre. attenuation = dB Determine the attenuation per unit length of the fibre. attenuation per unit length = dB km–1
9702_s13_qp_41
THEORY
2013
Paper 4, Variant 1
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10 Distinguish between sharpness and contrast in X-ray imaging. sharpness: contrast: State two causes of loss of sharpness of an X-ray image. 1. 2. Data for the linear attenuation coefficient μ of X-ray photons are given in . μ / cm–1 bone muscle 2.85 0.95 A parallel beam of X-rays is incident, separately, on a thickness of 3.5 cm of bone and on a muscle of thickness 8.0 cm. Calculate the ratio intensity of X-ray beam transmitted through bone intensity of X-ray beam transmitted through muscle . ratio = Use your answer in to suggest whether an X-ray image of the bone and muscle would show good or poor contrast.
9702_s13_qp_43
THEORY
2013
Paper 4, Variant 3
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12 An optic fibre is used for the transmission of digital telephone signals. The power input to the optic fibre is 9.8 mW. The effective noise level in the receiver circuit is 0.36 μW, as illustrated in . 9.8 mW receiver circuit, noise 0.36 +W optic fibre 85 km input circuit The signal-to-noise ratio at the receiver must not fall below 28 dB. For this transmission without any repeater amplifiers, the maximum length of the optic fibre is 85 km. Calculate the minimum input signal power to the receiver. power = W Use your answer in to calculate the attenuation in the fibre. attenuation = dB Determine the attenuation per unit length of the fibre. attenuation per unit length = dB km–1
9702_s13_qp_43
THEORY
2013
Paper 4, Variant 3
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Questions Discovered
77