Method and apparatus for overload protection for a photomultiplier tube

A photomultiplier tube protection apparatus comprising:

• (a) a photomultiplier having a anode, a plurality of dynodes, and a last dynode having an output signal, wherein the photomultiplier apparatus also has a focus electrode;
• (b) a high frequency amplifier for amplifying the anode signal and the output signal to generate a high frequency output signal;
• (c) a discriminator to compare the high frequency output signal such that if the high frequency output signal exceeds a predetermined threshold the discriminator will produce a logic high on a first line and a complimentary logic low on a second line;
• (d) a means for counting pulses on the complimentary lines such that if the means for counting exceeds a certain value it will send a signal on the first line and a complimentary signal on the second line;
• and
• (e) a means for controlling high voltage connected to receive a control signal from a means for counting, wherin the means for controlling high voltage has a voltage control output, and wherein the means for controlling high voltage is connected to the focus electrode.