Airborne radionuclides onto pine needles collected in the vicinity of the nuclear power plant.

Contents of 137Cs, 54Mn and 60Co in pine needles were investigated in the vicinity of the nuclear power plant in Tsuruga-shi, Fukui Prefecture. Concentrations of 54Mn and 60Co decreased, independent of the 137Cs level, with the increase of the distance from the plant and showed a similar pattern of distribution to that determined by the Gaussian plume model under the slightly unstable stability condition of the atmosphere. These nuclides were so efficiently retained in pine needles that any of them could not be readily removed by washing with water. The differentiation in retention was supposed to be hardly effected by rainfall and other weathering processes among these nuclides. The retention of radionuclide in pine needles was examined by using the radioactivity ratio of 54Mn to 60Co. The values gradually decreased during the period studied with the rate depending only upon the physical decay constants. It was suggested that to some extent radionuclide was retained in pine needles during at least two years and that there was not so great an additional load of these nuclides during that term.