An apparatus for the measurement of radon in sea water

For the determination of the low concentration of 222Rn in sea water, an improved 222Rn extraction and counting system was developed. The 222Rn in a 20l sample bottle was extracted from sea water with helium and collected in a charcoal trap cooled with dry ice and alcohol. The 222Rn extraction is accomplished by two circulation loops in a closed system: one is the rapid extraction loop of 222Rn from sample water by violent gas bubbling and strong agitation, and the other is the adsorption loop of 222Rn with a cooled charcoal trap. Successively, the 222Rn was desorbed from the trap by heating and transferred to a scintillation cell coated with ZnS(Ag). Following these procedures one can process a sample in 100 min with an overall efficiency (extraction-transfer-counting) of 57 %. Some results of 222Rn and 226Ra concentrations in coastal sea water are reported. (author)