The effect on the Pacific and Indian Oceans of the radioactive fallout have been systematically studied by the present authors for many years. In this study, the content and distribution of
137Cs, plutonium isotopes (
238Pu,
239Pu,
240Pu and
241Pu) and americium (
241Am) which is a decay product of
241Pu on the Southern Ocean surface are reported.
Water samples were collected south of Australia and New Zealand in 1977-1978. Above radioactive nuclides were precipitated from a large amount of sea water on board and brought back to the land laboratory.
137Cs was coprecipitated with ammonium phosphomolybdate. Plutonium and americium were coprecipitated with magnesium hydroxide. The determination of
137Cs was done by gamma-spectrometry. For plutonium and americium, alpha-spectrometry was used after the separation of these nuclides from a bulk of magnesium hydroxide precipitate by using ion exchange resin method.
The result of determination showed that content of
137Cs ranged from 0.02 to 0.15pCil
-1,
239+240Pu from 0.2 to 2.5×10
-4pCil
-1,
241Am from 0.2 to 0.5×10
-4pCil
-1. The ratio of
238Pu to
239+240Pu was 20 to 160%. The comparison between these results and those previously obtained in the Pacific and Indian Oceans will be done.
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