Which statement is NOT descriptive of a photomultiplier tube?

Which statement is NOT descriptive of a photomultiplier tube?

• A. Emits electrons proportionally to initial light absorbed
• B. Must be shielded from stray light
• C. Cannot be used with a chopper
• D. Amplifies the initial signal

Answer: (C)

A photomultiplier tube converts light into an electrical signal by emitting electrons from a photocathode when photons arrive, then amplifying that signal through a dynode chain. The number of electrons emitted is proportional to the light intensity hitting the photocathode, within the device’s linear operating range. Because PMTs are extremely sensitive, stray light can produce unwanted signals, so shielding and careful optical design are essential. The electron cascade at the dynodes provides substantial gain, turning a small photoelectric signal into a large, measurable current. The idea that a photomultiplier tube cannot be used with a chopper isn’t accurate—PMTs can detect modulated light from a chopper and are commonly used in time-resolved or phase-sensitive measurements, where the chopper helps reduce background noise and enhance signal fidelity.

A photomultiplier tube converts light into an electrical signal by emitting electrons from a photocathode when photons arrive, then amplifying that signal through a dynode chain. The number of electrons emitted is proportional to the light intensity hitting the photocathode, within the device’s linear operating range. Because PMTs are extremely sensitive, stray light can produce unwanted signals, so shielding and careful optical design are essential. The electron cascade at the dynodes provides substantial gain, turning a small photoelectric signal into a large, measurable current. The idea that a photomultiplier tube cannot be used with a chopper isn’t accurate—PMTs can detect modulated light from a chopper and are commonly used in time-resolved or phase-sensitive measurements, where the chopper helps reduce background noise and enhance signal fidelity.