APPLICATION OF EXCESS PB-210 DATING METHOD TO STALACTITES

The excess Pb-210 dating method was applied to two young straw stalact ites collected from a cave in southern Okinawa Island, Japan. The Pb-2 10 profiles only in the matrix of the straws exhibited an exponential decrease with distance from the tip. The Pb-210 profiles of th, two st raw samples gave the values of 2.2 and 5.9 mm/y for longitudinal growt h 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 concentration s in the cave air and the ground water running through the central cha nnel of the straws. During growing process of the straws, a part of th e Pb-210 will be adsorbed on the tip of straw, and they are supposed t o be incorporated into matrix part during reprecipitation of CaCO3.