Photoemissive materials

The very high reactivity of the alkali metals, even in compound form, requires that these compounds be prepared in high vacuum. Since these are used as photoemissive materials, inside photomultiplier tubes, this is not a problem in use, but detailed studies of properties and even composition are difficult k Usually, such materials are made by allowing alkali vapor to come in contact with a thin film of the group V or VI element. Ffar crystallographic studies, however, powders have been used. Temperatures from 130 to 240°C have been used the alkali vapor has been released from a compound such as the... 

The scintillations (visible hght photons) from the crystal fall on the cathode of the PMT, which is made of a photoemissive material such as indium antrmonide. Photoemissive... 

In photomultiplier-based detectors, the incoming ion beam is first converted to a photon beam when ions strike a scintillation material. The emitted photons are amplified and detected by a conventional photomultiplier. The construction of a photomultiplier is similar to that of an EM, except that the conversion dynode, called the photocathode, is coated with a photoemissive material that emits electrons when struck by photons. Photomultipliers are usually employed in combination with postacceleration devices, which are discussed next. 

The (CsSb) photocathode is typical of most classical photoemissive materials in that it can be modeled as a collection of homogenous semiconductor microcrystals with moderate bandgap energy, low electron affinity, and high... 

A.H.Sommer Photoemissive Materials (John Wiley and Sons, New York, London, Sydney, Toronto 1968) p. 222ff. 

The scintillations (visible light photons) from the crystal fall on the cathode of the PMT, which is made of a photoemissive material such as indium antimonide. Photoemissive materials release electrons when struck by photons. Electrons ejected from the cathode are accelerated to the first dynode, generating a larger number of electrons. The electron multiplication process occurs at each successive dynode, resulting in approximately 10 electrons reaching the anode for every electron that strikes the cathode. The amplitude of the current pulse from the photomultiplier is proportional to the energy of the X-ray photon causing the ionization in the crystal. 

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