A2 Daily A Level Physics question
An X-ray beam in a dental clinic passes through a protective panel. For this beam energy, the panel’s half-value thickness (HVT) is 2.0 mm. If a 6.0 mm thick panel is used, which option best describes the transmitted intensity compared with the incident intensity?
Answer
The correct answer is B.
Correct: B — about one-eighth of the incident intensity. Six millimetres is three HVTs (6.0/2.0), so the beam halves three times, giving one-eighth of the original intensity. A assumes a linear drop with thickness (one-third), but HVT implies multiplicative halving. B is correct because three successive halvings occur for three HVTs. C corresponds to only two halvings, which would be 4.0 mm, not 6.0 mm. D applies just one halving as if further thickness beyond one HVT had no extra effect.