Abstract
The determination of natural radioactive nuclides was carried out for 7 travertine samples collected from Tamagawa hot spring by means of the non-distructive γ-ray spectrometry and of the α-ray spectrometry. From the former measurements, the relative activity strength, due to 228Ra, 226Ra, and 228Th, and their ratios was obtained in comparison with the photopeak strength due to respective daughters, 228Ac, 214Bi, and 212Pb, and with the results from a monazite sand standard. One travertine sample was engaged to the α-ray spectrometric determination of Th isotopes after the chemical purification using a 234Th-yield tracer. On the basis of the resultant absolute content of 228Th, the 228Ra and 228Th contents in the remainder samples were evaluated to be the range of 3-80 Bq (81-2160pCi) /g and 2-20Bq (54-540pCi) /g, respectively. These radioactive nuclides were verified to exist almost within a Hokutolite small crystals up to 90% and there are apparently the radioactive disequilibrium relations between 228Ra and 228Th among freshly deposited travertines. The presence of 227Ac in Hokutolite was also suggested from the detection of 227Th owing to 215Po-αpeak.
