Device for accurately measuring small amounts of radiant energy

Claim 1

RADIANT ENERGY MESURING MEANS COMPRISING (A) A PHOTO-MULTIPLIER TUBE HAVING A PLURALITY OF ELECTRODES INCLUDING, (B) A PHOTOSENSITIVE CATHODE, (A) AN ELECTRODE FUNCTIONING AS AN ANODE, AND (D) A PLURALITY OF INTERMEDIATE DYNODES; (E) INPUT CIRCUIT MEANS FOR APPLYING BETWEEN THE CATHODE AND AT LEAST ONE, BUT LESS THAN ALL OF SAID DYNODES SUCCESSIVELY HIGHER LEVELS OF A HIGH FREQUENCY VOLTAGE, SAID LAST DYNODES BEING ACTIVE AND THE REMAINING ELECTRODES BEING INACTIVE; (F) MEANS FOR SQUARE-WAVE MODULATING SAID VOLTAGE AT A LOW FREQUENCY RATE TO PRODUCE GROUPS OF HIGH FREQUENCY PULSES AT SAID LOW FREQUENCY RATE WHEN SAID CATHODE IS STIMULATED BY RADIATION; (G) OUTPUT CIRCUIT MEANS COUPLED TO THE ANODE ELECTRODE; (H) LOW FREQUENCY MEASURING CIRCIT MEANS RESPONSIVE ONLY TO SAID LOW FREQUENCY AND SUPPLIED BY SAID OUTPUT CIRCUIT MEANS; (I) MEANS ELECTRICALLY CONNECTING THE INACTIVE ELECTRODES TO ONE OF THE ACTIVE DYNODES TO THUS PROVIDE D.-C. BIAS BETWEEN SAID ELECTRODE FUNCTIONING AS AN ANODE AND THE INACTIVE ELECTRODES AT A SUFFICIENTLY LOW LEVEL SO THAT THESE ELECTRODES REMAIN INACTIVE DURING OPERATION OF THE TUBE, THE ACTIVE DYNODES CONSTITUTING A FIRST GROUP OF SUCCESSIVE DYNODES ADJACENT TO THE CATHODE AND THE INACTIVE DYNODES; AND SECOND GROUP OF SUCCESSIVE DYNODES; AND (J) OUTPUT IMPEDANCE MEANS CONNECTED TO SAID ANODE FOR DEVELOPING AN OUTPUT SIGNAL AT SAID LOW FREQUENCY ACROSS SAID IMPEDANCE, SAID OUTPUT IMPEDANCE MEANS BEING OF EXTREMELY HIGH OHMIC VALUE, IN THE ORDER OF MEGOHMS.