摘要：For investigation of the natural level of radioactivity, the samples of hot spring water at Misasa spa area were collected several times from June 1963 to December 1965, and concentration of 226Ra, natural U, 222Rn, Ca ion, Cl ion, SO4 ion were determined. The sampling places were distributed to cover all area of spa in order to know the mean value of radioactivity level. Among those 15 sampling places, springs containing rather higher concentration of radioactive nuclides were crowded at the center part of Misasa area, corresponding to the north side of Santoku river. Besides, the concentration of 226Ra in spring water was far higher than the radioactive equilibrium value calculated from the content of natural U. The habitants in this area have a custom to drink the spring water usually, so hygienic problem was discussed comparing the maximum permissible concentration recommended by ICRP and NBS in the USA conveniently. The mean value of natural U was 2 μg/liter, and that of 226Ra was 5.4 pCi/liter. Comparing with 1/30 of the maximum permissible concentration in water for occupational people which was recommended by ICRP, the concentration of natural U was much lower, but the value of 226Ra was near to 1/30 of recommended concentration. The mean value of the concentration of 226Rn in spring water was 1.5×10-2 μCi/liter and much higher than 1/30 of the maximum permissible concentration recommended by NBS.
