CHEMICAL-COMPOSITION AND RADIOACTIVITY IN HOKUTOLITE (PLUMBIAN BARITE) COLLECTED AT PEITO HOT-SPRING, TAIWAN

Chemical composition and radionuclide concentrations were determined f or hokutolite, plumbian barite, collected at Peito hot spring, Taiwan. The hokutolite, precipitated on the surface of the base rock, was scr aped into 20 layers from the surface. Barium and Pb were determined by inductively coupled plasma-atomic emission spectroscopy, and Ra-228, Ra-226 and Pb-210 were determined by gamma-ray spectrometry. Compariso n of the Ra-228/Ra-226 activity ratio at the surface of the hokutolite with that of the hot spring water suggests that the hokutolite has be en isolated from the stream Soi 60 years. Significantly low fractions of (Ba, Pb)SO4 and changes in Ba/Pb mole ratio in the middle layers of the hokutolite suggest a change of growth condition at that time. Usi ng the smooth and continuous decline in Ra-228/Ra-226 activity ratio o bserved in the upper layers of the hokutolite, the growth rate of 0.17 mm year(-1) was estimated. (C) 1997 Elsevier Science Ltd.