Seasonal variations of radionuclide concentrations in pine needles

Seasonal variations of radionuclide concentration in pine needles (Pinus Thunbergii) were examined. The seasonal variations were classified roughly into two types, one represented by the periodical variation of¹³⁷Cs concentration and the other represented by a linear decrease of¹⁰³Ru concentration when plotted on a semi-log scale. Weathering half-lives for the latter type of nuclides were estimated and a fairly good consistency in the half-lives for different nuclides was observed irrelevant to their radioactive half-lives.