A
vacuum phototube with additional amplification by electron multiplication. It consists of a photocathode,
a series of dynodes, called a dynode chain on which a secondary-electron multiplication
process occurs, and an
anode. According to the desired
response time, transit time, time spread, gain, or low
dark current, different types of dynode structures have been developed, e.g. circular
cage structure, linear focused structure, venetian blind structure, box and grid structure.
Some special dynode structures permit combination with additional electric or magnetic
fields. A strip dynode photomultiplier tube consists of a photocathode followed by
thin dynode material on an insulating substrate. In a continuous-strip photomultiplier,
two strip dynodes are arranged in parallel. A potential applied to the ends of the
two strips produces an electric field across the continuous strip dynodes, giving
rise to electron multiplication along the dynodes. In a
resistance-strip magnetic photomultiplier, a uniform magnetic field is applied to the planes
of the strips, so that the electrons travel in the crossed electric and magnetic fields.
A channel photomultiplier tube photocathode consists of a
channel electron multiplier (
CEM) system for the photoelectrons, and an
anode to collect the final electron current. The basic part of the
CEM is a tube with a semiconducting inner surface. In general it is curved in order to
inhibit the
acceleration of positive ions towards the photocathode. A number of small channels called microchannels
can be constructed in arrays for imaging applications.
Source:
PAC, 1995, 67, 1745
(Nomenclature, symbols, units and their usage in spectrochemical analysis-XI. Detection
of radiation (IUPAC Recommendations 1995))
on page 1753
See also:
PAC, 1982, 54, 1533
(Glossary of terms used in nuclear analytical chemistry (Provisional))
on page 1548