The 137Cs concentration in an undisturbed upper layer of naked land in Fukuoka Prefecture decreased exponentially from 1969 to 1999 with the apparent half-life of 7 years. The ratio of 137Cs concentration in the lower layer of the soil to that in the upper layer was about 1/5. The concentration of 137Cs, 40K, and stable Cs and the soil profile consisting of loss on ignition, pH, and electric conductivity were determined in the 48 samples collected in the forests and the neighboring naked land from 1991 to 1998. The 137Cs concentration in the forest soils ranged from 1 to 424Bq/kg dry wt, 131Bq/kg dry wt on average, although 137Cs was hardly detected in the naked soil around the forest. There was no regional difference in the distribution of the 137Cs concentration, and it varied with pH and electric conductivity in the soil. Further, it tended to be higher in the deciduous woodland than in the evergreen woodland.
There is a slight possibility that radiopharmaceutical administrations are infiltrated to the subcutaneous tissue at intravenous administration. 201Tl has a long effective half life at subcutaneous tissue. It thus appears that there is some risk for radiation dermatitis when 201Tl is injected subcutaneously. To estimate radiation dose from extravasated 201Tl chloride, we created simple models. An absorbed dose to the basal cell layer of skin because of an inadvertent intravenous injection of 201Tl chloride was calculated from these models. The result indicated that extravasated 201Tl chloride may cause radiation burdens at high specific activity.
A simple alpha-track measurement technique for the equilibrium equivalent thoron concentration (hereafter called EETC) using a CR-39 detector was discussed. Detection properties of the CR-39 detector were examined with regard to detection efficiencies for incident energy and angles, respectively. Since more than 90% of the EETC is dominated by the 212Pb concentration, its practical evaluation can be achieved even though the 212Bi concentration is ignored. In this technique, the CR-39 detector is directly placed on a filter after an air sample is taken and an adequate time elapses (radon progeny completely decay). In order to confirm the reliability of measured values, the technique was compared with an alpha spectroscopic method. There was a relatively good agreement between the two.