Gamma camera (A-level only) Flashcards – AQA A-level Physics (7408)

What does a photomultiplier tube do?

It converts a weak flash of light into an electrical pulse and amplifies the signal.

How does a photomultiplier tube’s photocathode release electrons?

Incident photons release electrons by the photoelectric effect.

What accelerates electrons from the photocathode towards the first dynode?

A potential difference.

What happens when an electron strikes a dynode in a photomultiplier tube?

It releases several secondary electrons.

How are electrons accelerated between successive dynodes in a photomultiplier tube?

Successive dynodes are held at increasingly positive potentials.

What happens to the multiplied electrons at the anode of a photomultiplier tube?

They are collected, producing an electrical pulse much larger than the initial photoelectric signal.

What does a gamma camera image?

The distribution of a gamma-emitting radioactive tracer in the body.

How does a gamma camera’s lead collimator help preserve positional information?

Its channels preferentially allow photons travelling in particular directions to reach the detector.

What happens when gamma photons reach the scintillation crystal in a gamma camera?

They can produce flashes of light. The crystal is commonly sodium iodide.

What is the role of the photomultiplier tubes in a gamma camera?

They detect the light flashes and produce electrical signals.

How does a gamma camera estimate the position of a detected event?

It uses the relative signals from the photomultiplier tubes.

How are detected events used to form a gamma camera image?

Many detected events are combined electronically to show the tracer’s distribution.