Application of excess Pb-210 dating method to stalactites

摘要

The excess Pb-210 dating method was applied to two young straw stalactites collected from a cave in southern Okinawa Island, Japan. The Pb-210 profiles only in the matrix of the straws exhibited an exponential decrease with distance from the tip. The Pb-210 profiles of th, two straw samples gave the values of 2.2 and 5.9 mm/y for longitudinal growth rates. The excess Pb-210 is distributed uniformly over the outer and inner surfaces of the straws. Such an excess of Pb-210 is presumably produced from the airborne Rn-222 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 Pb-210 will be adsorbed on the tip of straw, and they are supposed to be incorporated into matrix part during reprecipitation of CaCO3. [References: 10]