The thoron chamber system has been set up. It mainly consists of two parts: an exposure chamber and a thoron gas generator. The exposure chamber is a 150Lcylindrical vessel, made of stainless steel. Four metal tubes are attached to the lid of the chamber. They are used to supply/exhaust radon/thoron gas and to take air samples. The gas generator is a 10Lstainless steel cylindrical vessel. The vessel is filled with thorium-rich ceramics. After connecting the exposure chamber and the generator, thoron gas circulates through the system with an external pump. The thoron concentration depends on the flow rate of the circulation. Radon and thoron concentrations are measured with scintillation cells after taking a sample promptly. Two types of passive radon detector were examined with the thoron exposure chamber system. They were exposed to thoron-rich air for 4 days. The mean thoron and radon concentrations throughout the exposure period were 2529 and 230Bq/m3, respectively. One detector provided 2913Bq/m3as the measured radon concentration. The other detector provided 1922Bq/m3.The evaluated concentrations were far away from actual values. Although the presence of thoron can be negligible in most cases, it is necessary to check the detection response to thoron on the radon detector with the proposed test before practical use.
The method to calculate the hydrogen concentration in metal specimens is given by tritium counts with the liquid scintillation counter. As segments to measure, Ni3Alintermetallic compound crystals were used. Tritium was charged to crystals with the method of cathode charging. The charged tritium was transported by diffusion and released from specimen surface. The tritium releasing rate was calculated from the increasing rate of tritium activity. Then the concentration of hydrogen at the surface was calculated from tritium counts. The outcome showed that the hydrogen concentration decreases at specimens surface by elapsed time. Then, the behavior of tritium diffusion was affected by doped boron (up to 0.235 atom%Band 0.470atom%B) inNi3Alcrystals. As the amount of boron increased, the tritium diffusion coefficient decreased. And the hydrogen concentration varied with the amount of boron. After passing enough time, the hydrogen concentration in crystals with boron was much larger than the one without boron. Since it is very likely that the hydrogen concentration is affected by the number of hydrogen sites in the crystal, it is obvious judging by these phenomena, that by doping boron, numbers of hydrogen trapping sites were created. As the hydrogen distribution becomes homogeneous after passing enough time, it is possible to measure the hydrogen concentration in all the crystals from β-ray counts at specimens surface.
A laboratory experiment of accumulation ana excretion of radionuclides (125I, 57Co, 141Ce, 103Ru, 85Sr, 137Cs, 54Mn) in juvenile Japanese flounder was carried out in order to elucidate the genetic factor intervening in the mineral balance, which possibly caused the fluctuation of so-called concentration factors. Fish originating from two populations, namely clone brood and hatchery-reared brood, were used in the present study. The variance of concentration of radionuclides was compared in terms of the radionuclide activity ratio, which was defined by radionuclide concentration in fish normalized by that in surrounding water. In general, narrower variations of concentration were observed in clone brood than in hatchery-reared brood, and significant differences were observed for57Co, 141Ceand137Csin the accumulation process and for five radionuclides other than125Iand103Ruin excretion process. The present study suggested that a probability of application of clonal fish would be advantageous in experimental assessments of biological effects of environmental contaminants in the sea.