What Is A Photomultiplier Tube And How Does It work?

Among the photosensitive devices in use today, the photomultiplier tube is a multipurpose device that offers extremely high sensitivity as well as a fast response.

This tube involves a photocathode followed by focusing electrodes, an electron collector, and an electron multiplier in a vacuum tube. At the point when light enters the photocathode, the photocathode radiates photoelectrons into the vacuum. These photoelectrons are then coordinated by the centering cathode voltages towards the electron multiplier, where electrons are increased by an optional emission cycle. With the help of an anode, the multiplied electrons are gathered as an output signal. Photomultiplier Tubes provide very high sensitivity as well as extremely low noise among the photosensitivity devices because of the secondary-emission multiplication. These photosensitive devices are used to identify radiant energy in the visible, ultraviolet, and near infrared-regions.

The photomultiplier tubes are also appreciated due to their incredible features, including low noise, fast time response, and a choice of large photosensitive areas.

Mechanism of operation of the photomultiplier tube:

A Photomultiplier tube uses two different scientific principles to intensify the effect of a single incident photon.

ü  Photoelectric Effect: In which photons interact with the photocathode to create electrons.

ü  Secondary Emission: The electrons are multiplied as they impact the string of dynodes, each of which has a higher voltage for crucial detection at the anode.

Construction of photomultiplier tubes:

A Photomultiplier is a vacuum tube that contains an input window, focusing electrodes, a photocathode, an electron multiplier, and an anode.

Ø  Light that passes in photomultiplier tubes is detected as an output signal with the help of the following procedures.

Ø  Light enters through the input window.

Ø  Light stimulates the electrons in the photocathode so that photoelectrons are radiated into the vacuum.

Ø  Photoelectrons are augmented and focused with the help of focusing anode onto the first dynode where methods for secondary electron emission duplicate them. This secondary emission is repeated at each of the successive dynodes.

Functions of photomultiplier tube:

Ø  These tubes are highly used for light detection of very feeble signals.

Ø  The Photomultiplier is a photo-emissive device in which the absorption of photon results in radiation of electrons.

Ø  It is one of the best vacuum tubes and also known as vacuum phototube.

Ø  It is a visible range photon sensor.

Ø  These tubes are used as a detector, which helps to change photons into electrons so that they can be detected. 

Initially developed as a more responsive television camera, these tubes are now found in many applications.  The photomultiplier tube is used in conjunction with scintillators to detect ionizing radiation, in research laboratories to measure the intensity as well as spectrum of light-emitting materials, and in many spectrophotometers. It is also used in numerous medical equipment design, gamma camera, and as a flying-spot scanners.