DF (decontamination factor) of two types of air filter was investigated against 198Au aerosol particles with AMAD (activity median aerodynamic diameter)=1.2μm and σg (geometric standard deviation)=2.0. One of the filters, SO filter, is HEPA (high efficiency particulate air) filter media with 46mm∅, and the other is HE-40 T (cellulose-glass fiber filter for dust sampling) filter media with 40mm∅. DF of the SO filter was found to be over 5×104 at air flow rate of 1l/mm. And DF of HE-40 T filter was determined to be 94±4 at the same airflow rate. In the multistage HE-40 T filter system, DF decreased at each succeeding stage. It was confirmed by numerical simulation that the decrease of DF was not inconsistent with the decrease of collection performance in each successive filter. It was also confirmed that DF could be predicted by the numerical simulation, if particle penetration function of filter and size distribution function of radioactive aerosol particles were known.
Natural radiation is closely related to radiation protection in various aspects. The clarification of its usefulness in the fields of applied nuclear energy and radiation is of importance for their sound utilization. In this paper, the effective dose equivalent due to external natural radiation in Japan was estimated for each prefecture together with its standard deviation, maximum and minimum values based on our nation-wide survey. The average effective dose equivalent due to external natural radiation was 0.59±0.14mSv/y. Using these estimated values, the significance of the results of natural radiation measurements in the fields of nuclear energy application has been discussed in the four aspects: 1) Standard for the dose cognition of artificial radiation, 2) utilization of regional differences of natural radiation dose for the acquisition of public acceptance of artificial radiation, 3) explanation of monitoring results, and 4) epidemiological studies for the analysis of low dose biological effects.
The influence of flow velocity and particle size distribution on the dispersion coefficient of water in saturated flow has been studied experimentally. The dispersion coefficient of water was determined by means of the comparison of theoretical effluent curve with effluent concentrations of tritium through porous medium. As the results of measurements, it was found that the dispersion coefficient was proportional to the 1.2th power of flow velocity in all cases of particle size distribution. The dispersion coefficient in the porous medium with a given size distribution agreed sufficiently with the volume mean of that of each particle size, and it was found that the dispersion coefficient was almost all proportional to the mean particle size of the porous medium.
The interaction of radiocobalt with glycine, alanine or aspartic acid dissolved in seawater was investigated under laboratory conditions by means of adsorption on Chelex 100 solvent extraction with dithizone or gel filtration chromatography. The results also were compared with those in freshly prepared or stored culture filtrates of chlorella, fishpond and offshore seawaters in which ionic radiocobalt was spiked, respectively. The distribution coefficients for Co in Chelex 100 and the extraction rates (%) of Co with dithizone in carbon tetrachloride decreased more greatly with time in the presence of the amino acids than in the control. The inhibitory effect of glycin on the adsorption of Co on the Chelex 100 was smaller than that of alanine or aspartic acid. In the fishpond and offshore seawaters or freshly prepared chlorella culture filtrate, the distribution coefficients for Co in Chelex 100 were somewhat greater than in the control, while no significant difference was observed in dithizone extraction. The results of Sephadex G-10 gel filtration chromatography for Co showed that the higher molecular species of Co associated with the amino acids occurred after several days ageing and then increased together with decreasing in the lower molecular species.
We have already recognized that Zn-DTPA (diethylenetriaminepentaacetic acid) is less toxic than Ca-DTPA when they are administered orally to rats. In this study, in order to estimate exactly the safety of Zn-DTPA by the oral administration in humans, by evaluating the degrees of damages in the different animal species between beagle dogs and rats, we examined the toxicity of Zn-DTPA in beagle dogs according to the same methods as the rat, and then the results were compared with those in the rat. Zn-DTPA was administered daily to beagle dogs for 1 month, with the doses of 30, 150, 300μmol/kg body weight. The decreases of body weight, hemorrhage and congestion, and vascular expansion of the lamina propria mucosa and under the serious membrane of the small intestine, and the slight damages of kidney were observed. These changes were similar to those in rats at the same dose. As a result, it is recognized that there are almost no differences on the Zn-DTPA toxicity between dogs and rats, therefore the safety of orally administered Zn-DTPA in humans might be estimated from the results obtained in the animal experiments without considering the remarkable species differences.
Presented are experimental and theoretical determinations of multisphere moderated BF3 counter responses. Eight spheres are used with different thicknesses ranging from 1 to 14cm of polyethylene moderators, and the central thermal neutron detector is a 2 inch diameter BF3 counter. The counter responses were measured for thermal and monoenergetic neutrons of energies 0.051, 0.144, 0.350, 0.565, 1.20, 2.50, 5.0, 15.2MeV. Calculations of the counter responses were also carried out by using one-dimensional discrete ordinates transport code, ANISN-JR. The experimental and theoritical results were in a good agreement except in the case for 1cm thickness of moderator at neutron energies higher than 2.5MeV. Energy response functions were finally estimated by using the experimental and calculated results. The measured and calculated sensitivities of the counter for 252Cf neutrons also showed good agreements.
To identify characteristics of radiation dose and important parameters in calculation of the dose from the pathway through groundwater in shallow land burial of radioactive waste, calculation of dose, sensitivity analysis and pathway analysis were carried out under a specific calculation condition. Following results were obtained: (1) For groundwater migration scenario, the pathway of direct drinking of groundwater is an important one. (2) The critical pathway differs with nuclides and changes with time. (3) Doses from use of river or lake water are several orders of magnitude smaller than that from use of groundwater. (4) When the disposal site is located at a coastal area, the critical pathway is ingestion of sea products and the doses are several orders of magnitude smaller than those at an inland area. (5) The groundwater velocity and the distribution coefficient are important parameters in calculation of radionuclide concentration in groundwater.