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

摘要

A liquid scintillation spectrometry method for the determination of Th-234 in seawater with Th-230 as the yield tracer has been developed and validated. Th-234 is separated from the dissolved phase by an Fe(OH)(3) precipitation and is then purified using ion exchange chromatography. The counting source is prepared by taking the sample to dryness in a vial, redissolving in acid, and mixing with a scintillation cocktail. The instrument employed has a relatively low background (11 cpm) and the ability to separate alpha from beta activity on the basis of pulse shapes. The Th-234 + Pa-234m counting efficiency is 50% over the counting window employed. The limit of detection, using the above parameters, 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 alpha/beta separation, can also be used effectively.