| 摘要 |
PROBLEM TO BE SOLVED: To enable a photodetector to detect light over a wide dynamic range by using a photomultiplier tube and, at the same time, to protect the anode of the photomultiplier tube from excessively large currents. SOLUTION: The photodetector is constituted so that, when the anode current of a photomultiplier tube 1 increases and approaches the maximum allowable output of the tube 1, the electric current T1 flowing through the anode 3 of the tube 1 is broken by switching switches 5a and 5b and, at the same time, the outputs of dynodes 4 are sent to an arithmetic processing section 8 after the outputs are converted into digital values by means of an A/D converter 7 by switching a switch 12. Since the outputs of the dynodes 4 indicate the value corresponding to the quantity of the light made incident on the tube 1 similarly to the anode current, the processing section 8 calculates the quantity of the light made incident on the tube 1 based on the outputs of the dynodes 4.
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