抄録
The excess 210Pb dating method was applied to two young straw stalactites collected from a cave in southern Okinawa Island, Japan. The 210Pb profiles only in the matrix of the straws exhibited an exponential decrease with distance from the tip. The 210Pb profiles of the two straw samples gave the values of 2.2 and 5.9 mm/y for longitudinal growth rates. The excess 210Pb is distributed uniformly over the outer and inner surfaces of the straws. Such an excess of 210Pb is presumably produced from the airborne 222Rn which exists with high concentrations in the cave air and the ground water running through the central channel of the straws. During growing process of the straws, a part of the 210Pb will be adsorbed on the tip of straw, and they are supposed to be incorporated into matrix part during reprecipitation of CaCO3.
