Question

Describe the differences between the following and listany particular advantages possessed by one over the other:

(a) phototubes and photomultiplier tubes .

Answer 1

Solution:

A phototube or photoelectric cell is a type of gas-filled or vacuum tube that is sensitive to light. Such a tube is more correctly called a 'photoemissive cell' to distinguish it from photovoltaic or photoconductive cells. Phototubes were previously more widely used but are now replaced in many applications by solid state photodetectors.

Whereas photomultiplier tube is one of the most sensitive light detectors, and is still widely used in physics research.

PMTs (Photomultiplier Tubes) are used for light detection of very weak signals.
• It is photo-emissive device in which absorption of photon results in emission of electron.
• It is one of the class of vacuum tubes also known as vacuum phototube.
• It is visible range photon sensor.
• Earlier PMTs are of larger size having glass vacuum envelopes, now they are available in smaller sizes.
• Now-a-days PMTs are replaced by avalanche photodiodes, but still they are in use in variety of applications such as Raman spectrophotometry, Fluorescent molecular tagging applications and single bubble sonoluminescence.

phototubes can still have substantial advantages: They can have a lower dark current, leading to a lower noise equivalent power. They can be made with a large photosensitive area while still having a high detection bandwidth.

Photomultiplier also have some advantages such as

• Low transport delay
• Wide spectral response
• High stability

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