DETERMINATION OF TH-234 IN MARINE SAMPLES BY LIQUID SCINTILLATION SPECTROMETRY

A liquid scintillation spectrometry method for the determination of Th -234 in seawater with Th-230 as the yield tracer has been developed an d validated. Th-234 is separated from the dissolved phase by an Fe(OH) (3) precipitation and is then purified using ion exchange chromatograp hy. The counting source is prepared by taking the sample to dryness in a vial, redissolving in acid, and mixing with a scintillation cocktai l. The instrument employed has a relatively low background (11 cpm) an d the ability to separate alpha from beta activity on the basis of pul se shapes. The Th-234 + Pa-234m counting efficiency is 50% over the co unting window employed. The limit of detection, using the above parame ters, a 20 L sample, and a 400 min count is found to be 0.04 dpm L(-1) . It was also demonstrated that less advanced instruments, without alp ha/beta separation, can also be used effectively.