A historical account of the sequence of events which took place in the fields of radiochemistry and cosmochemistry since the days of William Smith Clark (1826-1886)'s visit to Japan in the 19th century (1876-1877) to the dawn of the atomic age during the middle of the 20th century is presented. It is pointed out that there exists a striking resemblance between the radioactive fallout from nuclear weapons tests and the formation of the solar system from the debris of a supernova explosion.
The effects of the oral administration of CBMIDA [catechol-3, 6-bis (methyleiminodiacetic acid)], given in drinking water, on the removal of plutonium in rats were compared to those of Zn-DTPA. Male Wistar rats received a daily dose of 120μmol/kg or 1, 200μmol/kg of CBMIDA or Zn-DTPA, given in drinking water, for 4 weeks after plutonium injection. The content of plutonium in bone, liver, kidney, spleen, and testis was measured by a liquid scintillation spectrometry after treatment of the organs by a wet ash method. The plutonium content of each organ in the 120μmol/kg groups of CBMIDA and Zn-DTPA was not significantly reduced. The content of plutonium in the 1, 200μmol/kg groups of both CBMIDA and Zn-DTPA was, however, significantly reduced, to 65.7% (p<0.001) and 76.8% (p<0.05), respectively of the control in bone, and to 66.6% (p<0.05) and 44.0% (p<0.01), respectively, in liver. There were no significant decreases in kidney, spleen, and testis in the 1, 200μmol/kg dose CBMIDA group, but there were significant decreases in these organs in the 1, 200μcmol/kg dose Zn-DTPA group. These results showed that, when given orally, CBMIDA was more effective in removing plutonium from bone than Zn-DTPA, a finding similar to the results were achieved with the intravenous injection of both agents in our previous study.
Concentrations of 14C in vegetation collected near a nuclear power plant with two boiling water reactors were measured by a liquid scintillation counting technique to estimate the effects of 14C released from the nuclear power plant on the environment. The average 14C concentration in the vegetation collected near the nuclear plant was about 20mBq/g carbon higher than that collected from the environment where there was no effect of nuclear power plants. The increase in the 14C concentration in the vegetation was attributed to photosynthetic uptake of 14CO2 discharged from the nuclear power plant under normal operation. The elevated level of 14C content in the vegetation enables us to evaluate the discharged rate of 14C from the nuclear power plant and has led to an estimation of 0.36TBq/(GW·a) which is comparable to values reported on other BWRs.
We planned to synthesize tritium-free water from natural gas which is presumed to contain no tritium. In the liquid scintillation counting method, tritium-free water is used to compensate for the background counts. To synthesize tritium-free water, we assembled an apparatus which is capable of oxidizing natural gas into water under conditions completely isolated from the environment. As previously reported, the quality of the water depends mainly on the material oxygen used. We synthesized water using conventional electrolyzed pure oxygen. Analysis by the electrolytic enrichment technique showed that there was almost no tritium in the synthesized water.
To estimate the dose equivalent (H1cm) of a person who may come into close contact with patients exposed to 201T1, dose rates around 15 adult patients (rest group: 8, exercise group: 7) have been measured with ionization survey meters. Measurements were carried out at 30min, 24h, 72h, 144h (or 120h) and 216h after the administration of 201T1Cl. Survey meters were set up at the height of the first cervical vertebrae (I), xiphoid process (II) and anterior superior iliac spines (III) with the patient in a standing posture, and at distances of 0.05, 0.5, 1.0 and 1.5m from the patient. The maximum H1cm rate of 18.37μSv/h per 74MBq was recorded at level II in the anterior projection. Doses in the posterior projection were similar to those at the anterior projection, however, in the right- and left-lateral projections the doses were lower than the anterior dose. The difference in doses between the rest and exercise groups was slight. The calculated effective half-life was 63.0h. H1cmS were 891, 196, 77 and 42μSv/w per 74MBq at distances of 0.05, 0.5, 1.0 and 1.5m, respectively. These H1cmS correspond to 84% of the total H1cmS (μSv/∞h). The family of a patient given 201T1 was one-third of the total H1cm at 0.05m, the dose did not exceed the dose limit described in recommendations-1990 of ICRP. However, it was a substantial dose for them. Staff doses in general wards and in special wards (ICU or CCU) were one-fourth of a total H1cm at 0.5m, these doses were the result of contact with 17 201T1 patients and 257 201T1 patients for one year. The dose of patient in the same room as patients given 201T1 were 42μSv/w at 1.5m; this dose did not exceed his dose limit of 100μSv/w. These results do not suggest that radiation protection is necessary when exposed to a patient given 201T1, but in the case of close contact with many 201T1 patients, it would be necessary when the radiation dose exceeds the limit.
Concentrations of uranium and thorium are measured in concrete samples by the neutron activation analysis. The samples composed of cement, sand and gravel are powdered using an agate mortar. Measured results show concentrations for thorium to be 2.4-2.7ppm, which are generally higher than those for uranium of 0.7-1.2ppm. This trend is consistent with that of the natural abundance for thorium and uranium in the earth's crust. This observation also agrees with the tendency of the concentration of thorium to be higher than that of uranium, as shown previously for the front glass of the cathode ray tube of television sets.
The concentrations of outdoor radon and its progeny were measured every three hours. An electrostatic collection method for radon and three count techniques for radon progeny were adopted to measure the concentrations continuously. The measurements carried out from Feburary 1991 to June 1992. The equilibrium equivalent thoron concentrations were also measured with a radon progeny monitor. The concentrations of radon and its progeny showed the same diurnal variation of a maximum in the morning and minimum in the evening. An averaged equilibrium factor (F) was 0.76 over the whole period. The ratio of radioactivity concentration, 222Rn: 218Po: 214Pb: 214Bi, was 1.00: 0.80: 0.78: 0.72 in outdoor air. In comparison with outdoor radon progeny, the outdoor concentration of thoron progeny was about 1/40 and human exposure was about one-tenth.