Content of plutonium, thorium and protactinium in sea water and recent coral in the North Pacific

The contents of plutonium isotopes ( 239 Pu and 238 Pu), thorium isotopes ( 232 Th, 230 Th and 228 Th) and protactinium-231 in sea water collected in the North Pacific, the East China Sea and the Japan Sea were determined. These nuclides were sequentially analyzed by α -ray spectrometry after separating them mainly with solvent extraction technique. The contents of 239 Pu in surface sea water ranged from 0.6 to 1.6 pCi/10001, 238 Pu/ 239 Pu activity ratios being 0.2∼0.7. The 228 Th/ 232 Th activity ratios for the North Pacific waters varied between 7.6 and 30, whereas the sample from the East China Sea showed the very high value, 65. The contents of 231 Pa are less than 6 percent of that in equilibrium with its parent 235 U. Furthermore, the analysis of plutonium isotopes in recent coral from Yoron Island was carried out and it was confirmed that plutonium isotopes have concentrated in recent coral with the concentration factor of about 1∼2×10 3 .