동해 남서부 유광대에서 226Ra과 228Ra의 농도 수직 분포

Abstract

Distributions of the naturally occurring radionuclides226Ra and 228Ra in the water column were studied at thesouthwestern part of the East/Japan Sea. Activityconcentration depth profiles in the thermocline (depth200 m) of 226Ra and 228Ra were obtained at four stationsalong a transect from 35ºN to 36ºN at 130º50E.The upper 150 m of the southwestern East/Japan Seaconsists of warm and saline water transported by theTsushima Current through the Korea/Tsushima Straitwith about 20 % originating from the continental shelfwaters of the East China Sea and the Yellow Sea withthe remaining 80 % from the Kuroshio Current waters(Nozaki et al., 1989).Radium was extracted from seven depths by pumpingseawater through MnO2-impregnated filters in tandemwith an overall extraction efficiency of 90 ± 6 %. The226Ra and 228Ra activity concentrations were determinedby gamma-ray spectrometry with well-defined geometry.226Ra activity concentrations in the water column showedminor variations in the upper 200 m with an average of1.9 ± 0.3 Bq m-3. The 228Ra activity concentrationsdecreased with depth from ~4 Bq m-3 at the surface to ~1Bq m-3 at depth 100 m reflecting the contribution of theTsushima Current water in the southwestern East/JapanSea.From the 228Ra/226Ra activity ratios in the upper 100 mwater column (Fig. 2), mixing ratios in the seawater atthe sampling site was estimated 228Ra were obtained at four stationsalong a transect from 35ºN to 36ºN at 130º50E.The upper 150 m of the southwestern East/Japan Seaconsists of warm and saline water transported by theTsushima Current through the Korea/Tsushima Straitwith about 20 % originating from the continental shelfwaters of the East China Sea and the Yellow Sea withthe remaining 80 % from the Kuroshio Current waters(Nozaki et al., 1989).Radium was extracted from seven depths by pumpingseawater through MnO2-impregnated filters in tandemwith an overall extraction efficiency of 90 ± 6 %. The226Ra and 228Ra activity concentrations were determinedby gamma-ray spectrometry with well-defined geometry.226Ra activity concentrations in the water column showedminor variations in the upper 200 m with an average of1.9 ± 0.3 Bq m-3. The 228Ra activity concentrationsdecreased with depth from ~4 Bq m-3 at the surface to ~1Bq m-3 at depth 100 m reflecting the contribution of theTsushima Current water in the southwestern East/JapanSea.From the 228Ra/226Ra activity ratios in the upper 100 mwater column (Fig. 2), mixing ratios in the seawater atthe sampling site was estimated