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Figure 3 shows the X-ray spectrum produced in a medical X-ray machine at a particular anode potential difference (pd) - AQA - A-Level Physics - Question 3 - 2019 - Paper 5
Question 3
Figure 3 shows the X-ray spectrum produced in a medical X-ray machine at a particular anode potential difference (pd). In an X-ray tube, electrons collide with a tu... show full transcript
Worked Solution & Example Answer:Figure 3 shows the X-ray spectrum produced in a medical X-ray machine at a particular anode potential difference (pd) - AQA - A-Level Physics - Question 3 - 2019 - Paper 5
Step 1
Explain how the continuous spectrum and the characteristic spectra are produced by these electron collisions.
Answer
When electrons collide with the tungsten target in an X-ray tube, they generate two types of spectra: continuous and characteristic.
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Continuous Spectrum: This smooth curve results from electrons decelerating as they interact with the tungsten atoms, converting their kinetic energy into X-ray photons. The maximum energy is limited by the kinetic energy of the accelerating electrons, corresponding directly to the anode potential difference (pd).
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Characteristic Spectrum: This discrete spectrum arises from inner shell electron transitions. When outer electrons knock inner electrons out of their shells during collisions, vacancies are created. Electrons from higher energy levels fill these vacancies, emitting X-ray photons with specific energies unique to the tungsten target.
Step 2
Sketch on Figure 4 the X-ray spectrum produced when the anode pd is increased.
Answer
When the anode potential difference (pd) is increased, the entire X-ray spectrum shifts to the right. The peak energy of the spectrum increases proportionately, while the intensity at all points remains unchanged except for the peak height which may slightly increase. Thus, the new sketch shows a similar shape to the one in Figure 4, with shifted peak and endpoints to the right, starting at energy 0.
Step 3
Sketch on Figure 5 the X-ray spectrum of the X-rays that emerge from the filter.
Answer
The X-ray spectrum after passing through the aluminium filter displays a lower intensity in the lower energy region due to the absorption of weaker X-ray photons. The characteristic peaks may still be visible; however, the area under the spectrum is reduced. The sketch in Figure 5 shows a similar shape to that shown in Figure 4 but with an overall decrease in intensity, especially for lower energy X-rays.