Apparatus for Measurement of Concentration in the Atmosphere of the Short-Lived Solid Decay Products of Radon

摘要

1,191,982. Monitoring atmospheric radioactivity. COMMISSARIAT A L'ENERGIE ATOMIQUE. April 5, 1968 [April 13, 1967], No. 16457/68. Heading G1A. The concentrations of the short lived decay products of radon in the atmosphere are measured by depositing them on an intermittently moving filter strip, subsequently detecting separately the α and # particles emitted from the deposit, applying the α pulses to a two channel pulse height analyser to separate the components due to RaA and RaCSP1/SP and subtracting the RaCSP1/SP component from the # pulses to provide a measure of the RaB component. Sampling and detection apparatus. A filter strip 1, Fig. 3 extends between spools 2, 3, and passes through a sampling tube 6. At the start of a sampling interval, the inner tube 13 is lowered by an armature 11 to clamp the strip at the bottom of the tube 6 and the pump 8 is actuated to draw air through the filter strip. A punch 12 makes a perforation a distance D along the strip from the centre of the tube 6. At the end of the sampling period a cam switch 14 closes energise the solenoid 10 to raise the tube 13 and punch 12 and change over from the pump 8 to the pump 9. When the punch 12 closes the switch 20 an electromagnetic clutch 5 operates to move the strip until the perforation is detected by a photo-resistor 17. The deposited sample is then between a semi-conductor junction α-particle detector and a #-sensitive geiger tube 22 having an α opaque window (4mg/cmSP2/SP mica). Geiger tube 22 is surrounded by a compensating geiger tube 23, the outputs of the two tubes being connected to an anticoincidence circuit to eliminate background. Electrical circuit. The output of the α detector 21, Fig. 4, is fed through amplifiers 24, 25 to a pulse height analyzer 26, 27 and pulses due to RaA and RaCSP1/SP are each shaped (28, 29), integrated (30, 31) and applied to a recorder 34 which records them sequentially. The output of the # detector 22 is shaped at 40 and integrated at 41 and applied at T to recorder 34. The # output depends on both RaC and RaB. The RaCSP1/SP signal from integrator 31 is multiplied by 1À0004 at 43 to become representative or RaC and then subtracted from the # signal by connecting the signals to opposite ends of potentiometer 47 and the difference applied to recorder 34 at B as a signal representative of RaB. An extra channel may be provided whereby the total α count may be recorded.