Kodak DirectView CR 825 Theory Manual page 65

THEORY GUIDE
10DEC05
descending series of voltages. These voltages are connected to components in the PMT.
TG4825-1
Page In the graphic, example voltages are given.
65 of 120
Note
The HIGH VOLTAGE POWER SUPPLY provides a high negative voltage. The
PHOTOCATHODE is connected directly to the -600 V source. The FOCUSING ELECTRODE
in the PMT is set to -500 V. Next to the FOCUSING ELECTRODE are a series of DYNODES,
which are set at decreasing voltages until at the end is an ANODE which is set at 0 V.
3 The PHOTOCATHODE emits an electron when it is hit by a light photon. Because the
efficiency of the PHOTOCATHODE is less than 100%, the number of electrons is less
than the number of photons entering the PMT.
4 The negatively charged electron is influenced by the electrical field between the
PHOTOCATHODE at -600 V and the more positive FOCUSING ELECTRODE
at -500 V, pulling the electron toward the FOCUSING ELECTRODE.
5 When the electron moves toward the FOCUSING ELECTRODE, it is pulled by the more
positive DYNODE. When the electron hits the DYNODE surface, it reflects from the
surface and emits more electrons. At each DYNODE, the number of electrons increases,
more electrons are added, and all the electrons are attracted to the next more positive
DYNODE.
6 At the end of the PMT, all the electrons are attracted to the ANODE, which assembles
the electrons and sends the electrons to the PMT/DAS BOARD A5 in a small current
signal.
Optical