Photomultiplier Tube

NEW 4 Hamamatsu Photomultiplier Tube PCR Light Filters
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US $2,260.99

ET Enterprises Photomultiplier Tube With Cap 9826KB New
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US $1,509.11

SURFSCAN 6420 245569 R1307 SELEC TUBE PHOTOMULTIPLIER SELECTED
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Hamamatsu Photomultiplier Tube H283497 R130609
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US $1,200.00

NOx photomultiplier tube assy Thermo Environmental NOx analyzer 42 series
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4 Hamamatsu Photomultiplier Tubes w PCR Light Filters
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US $907.99

Why can photomultiplier tubes not be used with infrared radiation?

Why can photomultiplier tubes not be used with infrared radiation?

Short Answer: A PM tube doesn't operate in that wavelength.

A PM tube detects light which is generated from a scintillator. The scintillators are typically designed to scintillate as a result of a reaction with ionizing radiation.

Long Answer:

Photomultiplier Tubes

The purpose of the photomultiplier tube is to detect the scintillations and to provide an output signal proportional to the amount of scintillations. In doing this, photomultiplier tubes can provide amplifications of 1 E6 and higher.

Construction

Construction details vary from design to design; however, all photomultipliers have typical components. These common components are: the photocathode, the dynode assembly, an anode, voltage divider network, and shell. These components perform as follows:

• Photocathode - made of antimony - cesium composite. The purpose of the photocathode is to convert the light photons to electrons (called photoelectrons).

• Dynode Assembly - A series of electrodes used to amplify the signal. Each successive dynode has a higher voltage potential. The voltage gradient along the tube accelerates the electrons towards the anode. This works as follows: the photoelectron strikes the first dynode freeing one or more electrons. These electrons are drawn towards the second dynode. At the second dynode each electron frees one or more additional electrons. This process continues until the electron cascade reaches the anode. Through this process, the initial photoelectron is amplified, up to 106 times and higher. For an amplification of 106 an average of 4 electrons is freed by each incident electron reacting with each dynode (10 dynodes - 410 106).

• Anode - The anode collects the electrons and generates an output pulse.

• Voltage Divider Network - Splits the high voltage supply into the various potentials required by the dynodes.

• Shell - Supports the other components and seals the tube from stray light and stray electric/magnetic fields.

Output

The photomultiplier tube provides an output pulse which is proportional to the incident photons. The size of the pulse is a function of the energy of the light photon, and of the electron multiplication. Varying the HV to the photomultiplier varies the pulse height.

It is possible for stray electrons to be amplified by the dynode, creating an output pulse while no photon entered the tube. Those electrons can be spontaneously emitted from the photocathode or by the dynodes themselves. This output signal is commonly called dark current. Dark current increases with photomultiplier tube temperature, hence, temperature changes may cause the detector to "drift."