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GATE 2025 PH – Question 29

Nuclear and Particle Physics · particle accelerators and detectors · 1 mark · Multiple select

Nuclear radiation emitted from a Co 60 radioactive source is detected by a photomultiplier tube (PMT) coupled to a scintillator crystal. Which of the following option(s) is/are correct?

  1. γ radiation from Co 60 will directly hit the photocathode of the PMT without interacting with the scintillator crystal and produce a signal
  2. β radiation from Co 60 source interacts with the scintillator crystal, producing γ radiation, which will hit the photocathode of the PMT and produce a signal
  3. A mu-metal shield is put all around the PMT to nullify the effect of external electric fields
  4. A mu-metal shield is put all around the PMT to nullify the effect of external magnetic fields

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Correct answer: (D) A mu-metal shield is put all around the PMT to nullify the effect of external magnetic fields

Explanation

The scintillator converts deposited ionizing-radiation energy into optical photons detected by the PMT. Mu-metal has high magnetic permeability and shields magnetic fields, rather than electric fields.