A RADON DETECTOR SUITABLE FOR PERSONNEL OR AREA MONITORING

A radon detector is described which can be used to measure integrated radon exposure. Radon but not its daughters in the atmosphere to be sampled diffuses through a porous medium into a chamber with a sensitive volume of 28 cm3. A 60 V potential is maintained between a hemispherical screen and an aluminized mylar film covering a zinc sulfide (ZnS(Ag)) coated lucite light pipe. When 222Rn decays, 218Po, which is generally produced as a positively charged ion, is electrostatically collected on the aluminized mylar surface. Decay of 218Po (T1/2 = 3.05 min) produces scintillations in the zinc sulfide, which are recorded on a photographic film selected because of its sensitivity to the 4500 Angstrom radiation emitted by ZnS(Ag). The film is then developed and the exposure read by conventional densitometry. In this paper, the design of the device is described, and the results of field and laboratory tests are presented. The instrument has a capability of monitoring atmospheres which average between 40 pCi/l. and 550 pCi/l. of radon during a period of 170 hr. © 1969 Health Physics Society.