GB1010902A - Improvements in or relating to beta radiation monitors - Google Patents

Abstract

1,010,902. Beta radiation monitors. PLESSEY CO Ltd. March 6,1962 [March 20, 1961], No. 10048/61. Heading G1A. The invention relates to a beta radiation monitor for indicating whether the beta radiation from a radio-active material (not shown) is above or below a predetermined level and comprises a Geiger-Muller tube 3 the signal from which is fed to a rate circuit 5 and from there to an alarm circuit 12 through an amplifier 8. The monitor includes a shutter 1 which may be interposed between the material and the tube 3 having a beta source 4 whose radiation has that value of intensity required to cause the alarm 12 to operate. The thickness of the shutter is such that it will prevent external beta particles from entering the tube 3 but will have no effect on a gamma ray component of the radiation from the material, and the shutter may be rotatably, or horizontally removed as shown, from in front of the sensitive portion of the tube 3. The current i 1 at the output of the rate circuit 5 is the analogue of the impulse rate from the tube 3 produced by the incident radiation; part of this current i 2 passes through and is controlled by a variable resistance 6 connected as shown, the remainder i 3 (=i 1 - i 2 ) passes through a resistance 7 in parallel with the amplifier 8 which draws no input current. The voltage at point 9 therefore remains constant and the voltage at a point 10 changes by the product of i 3 and the value of the resistance 7. With the shutter moved in front of the tube the resistance 6 is varied until the currents i 2 , i 3 and hence the voltage at point 10 are sufficient to cause the alarm 12 to operate. If the shutter is then removed beta radiation from the material will cause the alarm to operate when the intensity reaches the same level as that of the source 4 on the shutter. The alarm signal may be in any chosen visual or audible form.