Uptake and loss of radioactive iodine by marine organisms were studied in the artificial seawater in which the concentration as well as chemical forms of both stable and radioactive iodine were controlled. The concentration factors of radioactive iodine by these organisms were clearly dependent upon the concentration of stable iodide ion in the culture media while the concentration of stable iodate ion did not affect the uptake and loss of radioactive iodine. It was observed that the higher the concentration of iodide ion was in the culture media the shorter the biological half-life of radioactive iodine became, and thus the lower the concentration factor resulted in.
We have developed a production system for18F-2-deoxy-2-fluoro-D-glucose (18F-2FDG), which assures reliable production with easy handling and reduces radiation exposures to the operator. Chemical procedures in this system are the same as manual method developed in NIRS. This system has 2 operation modes; one is remote controlled manual operation mode and the other is microcomputer controlled automatic operation mode. In remote controlled mode, we tested this system 5 times and18F-2FDG synthesized was supplied for clinical use once. The mean radiochemical yield of18F-2FDG from the target gas recovery with decay time correction was 8%, that is the same as in the manual synthesis. It took about 2 hours from end of bombardment (EOB) to end of synthesis (EOS) . Since this time is shorter than in manual synthesis, the available activity at EOS is increased.
Monitoring of workers who did iodination of protein was performed for 5 months on 10 persons. The activity in saliva was evaluated following the sum peak method by using a NaI (Tl) detector and a 400-channel analyzer. The concentration of125I in saliva ranged 4.65±2.1 cBq (1.26±0.57 pCi) /ml to 135±2.7 cBq (36.45±0.73 pCi) /ml and the average was 20.8±1.9 cBq (5.62±0.51 pCi) /ml. The ratio of concentration in saliva to used activity ranged (2.2±0.64) ×10-9 to (3.6±0.073) ×10-8 and the average was (8.1±1.1) ×10-9. The thyroidal uptake per iodination ranged 146 Bq (3.94 nCi) to 2700 Bq (72.9 nCi) . The ratio of the uptake to the used activity ranged from 7.3×10-5 to 5.4×10-6. The thyroidal absorbed dose ranged from 378μGy (37.8 mrad) to 4740μGy (474 mrad) . Monitoring of125I in saliva was proved to be a useful method to investigate the internal contamination of workers doing iodination.
A river water sample was irradiated with60Co γ-rays under aerobic conditions, and the changes of the organic substances in the sample were examined by the analyses of the dissolved organic carbon (DOC), organic composition, UV spectrum and molecular-weight distribution. By the irradiation, the DOC decreased with irradiation dose following the first-order kinetics. In addition, the changes of UV absorption and molecular-weight distribution showed that the considerable decomposition of polymeric aromatic structure, which is the characteristic of humic substances, took place by irradiation of relatively low dose. Since the γ-ray decomposition does not require any oxidizing agents and pH control, it will cause no compositional change of metallic elements in the water samples and has less chance of contamination. Therefore the method will be useful in, for example, geochemical studies of trace metals in natural waters.