APPARATUS FOR CONTINUOUS AND SIMULTANEOUS MEASUREMENT OF CONCENTRATION IN THE ATMOSPHERE OF THE SHORTLIVED SOLID DECAY PRODUCTS OF RADON

摘要

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 [alpha] and # particles emitted from the deposit, applying the [alpha] pulses to a two channel pulse height analyser to separate the components due to RaA and RaC1 and subtracting the RaC1 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 [alpha]-particle detector and a #-sensitive geiger tube 22 having an [alpha] opaque window (4mg/cm2 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 [alpha] detector 21, Fig. 4, is fed through amplifiers 24, 25 to a pulse height analyzer 26, 27 and pulses due to RaA and RaC1 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 RaC1 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 [alpha] count may be recorded.