Device for measuring physical quantities which the influence of a radioactive radiation intensity

摘要

1,100,693. Measuring radiation. NORTH AMERICAN AVIATION, Inc. May 28, 1965 [June 1, 1964], No.22843/65. Heading G1A. Apparatus for measuring the intensity of first source of radiation is provided with a second source of radiation of different energy and means responsive to signals derived from the radiation from the second source to adjust the sensitivity of the radiation detector or its circuit. The invention is applied to apparatus as disclosed in Specification 885,102 for measuring the volume of fuel in a tank. Gamma radiation from a Ce137 or Co60 source that has passed through the tank 32 is incident upon a scintillation counter to produce pulses of a height in a range L 1 . These pulses trigger only circuit 56 and pass to an integrating amplifier 80 feeding a pulse rate meter 24. The second source 34 is alpha emitting Am241 which produces pulses in scintillation counter 20 of a height centred on the division between ranges L 2 and L 3 ,so that half the Am241 pulses pass threshold circuit 60 and half only pass threshold circuit 58. If the sensitivity of the scintillation counter varies the distribution of the Am241 pulses between ranges L 2 and L 3 will change. The difference between the count rates in these channels is derived by an amplifier and used together with the actual values of the count rate to control the sensitivity of the photo-multiplier to keep the count rates equal. The sum of the count rates may also be used to adjust the gain of the pulse shaping circuits 66, 68, 70 to compensate for natural decay of the sources (which have been chosen to be approximately equal). As in Specification 885,102 a number of fuel tanks may be monitored by separate systems using the same output display.