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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
In an X-ray tube, electrons are accelerated towards the tungsten target by a high potential difference. When these electrons collide with the tungsten atoms:
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Continuous Spectrum: As electrons decelerate upon hitting the target, they transfer their kinetic energy to X-ray photons. This deceleration causes the emission of a continuous spectrum, known as Bremsstrahlung radiation, as the energy lost varies continuously.
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Characteristic Spectrum: Some electrons dislodge inner-shell electrons in the tungsten atoms, creating vacancies. Other outer electrons then transition to fill these vacancies, emitting X-rays at specific energies corresponding to the differences in energy levels. This behavior results in sharp peaks in the spectrum, known as characteristic X-rays.
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 peaks of the X-ray spectrum shift to the right, indicating that X-rays of higher energies are produced. The overall intensity of the spectrum also increases. The sketch should show the dashed line moving upward and to the right compared to the initial line in Figure 4.
Step 3
Sketch on Figure 5 the X-ray spectrum of the X-rays that emerge from the filter.
Answer
When the X-rays pass through the aluminium filter, some lower-energy X-rays are absorbed, which reduces the intensity at lower photon energies. The sketch should depict a similar spectrum to Figure 4, but with reduced intensity for lower energies, and the peak still to the right, remaining at a higher energy level.