PHOTOELECTRON MULTIPLIER

PURPOSE:To reduce the dark noise component based on the luminous phenomenon due to radioactive impurities and cosmic rays and perform the low- background light measurement by turning off a counter counting output pulses from the final dynode of a secondary electron multiplier electrode. CONSTITUTION:When outputs are obtained from both anodes 20A, 20B of a concurrent counting device 24, the gate of a counter 22 is closed, and the counter 22 does not count the output from the final dynode 17 of a secondary electron multiplier electrode 16A. When there are dark noises based on the luminous phenomenon due to radioactive impurities and cosmetic rays, the counting by the counter 22 is canceled. The measured light is weak and enters only into an photoelectric face 14A in the single photon phenomenon, and photons do not feed outputs to anodes 20A, 20B of the first system and the second system concurrently. The effect of dark noises is prevented, the S/N ratio is increased, and the measured light can be counted.