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 20
l 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 scintilla-tion 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.
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