Abstract: The usual method for the determination of ¹³⁷Cs in seawater is to enrich the nuclide using radiochemical procedure, and then measure the gamma-ray spectrometry with a high efficiency HPGe detector. But this method uses a fixed chemical recovery and will produce about 10%—20% measure error. In this paper, it is found that using ¹³⁴Cs as a tracer can notably reduce the error. Pre-experiments have been done to study the effects of factors on the chemical recovery. According to the results, an analysis process is suggested: transfer 50 liters environmental seawater to the container first, adjust its pH≤2; then add moderate Cs carrier and about 1.0 Bq ¹³⁴Cs, and add 10 g AMP after stir well;Finally stir about 4.0 hours manually, and then measure. When the measure time is 80 000 s, the LLD is 1.4 mBq/L, and the measure error is less than 5%. This method is not suitable for nuclear accident emergency monitoring.

Key words: tracer of Cesium-134, Cesium-137, gamma-spectrometry