The immersion model based on the meteorological dispersion of the cloud can not be applicable to the estimation of exposure dose near the release point. And it is also important to estimate the exposure of personnel in site of the reactor, and results of the estimation would be useful to know the exposure pattern of ⁴¹A which is released in normal operation of the reactor. In this paper the estimation was made of the external dose near the release point, comparing with those in immersion case, and the aspect of external dose from radioactive cloud in whole area of interest was figured out.
The calaulation was carried out under the following assumptions:
(1) The cloud is of the coning shape with a vertex angle 20° which corresponds to category D (stable) in Meade and Pasquill's classification.
(2) The condition of continuity of radioactivity holds and the distribution of the radioactive concentration is Gaussian in the radial direction of the cross section of the cloud.
The results show that the external dose near the release point from the coning cloud is in the same order as the maximum dose in immersion case and never exceeds it. Figures were given showing the effect of variation of release point height and iso-dose distribution near the release point. The error resulted from some simplifications of the original equation was within 10%.

View full abstract

²³⁹Pu-²³⁵U fueled fast critical assemblies are of interest to estimate properties of ²³⁹Pu fueled assemblies because of safety considerations and or limited plutonium availability. Numerical analysis for bare and reflected homogeneous cores and reflected Two-region cores are previously reported. It is concluded that the errors in the calculated critical size for a 5.0 v/o ²³⁹Pu fueled system reduce more than a factor of about 10 to 20, if an accurate experimental value of critical size of a critical assembly fueled by 0.5 v/o ²³⁹Pu and 4.5 v/o ²³⁵U is known.
In this report, a general mathematical formula, which is useful to explain the above conclusions more clearly, is obtained for bare homogeneous mixtures using multigroup diffusion approximation.
In order to predict the critical radius for the bare homogeneous ²³⁹PU system in an accuracy, 1%, the errors·for the experimental value of critical radius must be less than 0.1% for V^Pu/V^Fuel=0.05 and 0.2% for V^Pu/V^Fuel=0.1, where V^Pu and V^Fuel are the volume fractions of ²³⁹Pu and fuel (²³⁹Pu+²³⁵U) respectively. For the reflected Tworegion cores, the experimental errors required for the above accuracy must be less than 0.5% for the ratio of central ²³⁹Pu core region volume to total core volume of 0.1.

View full abstract

(1) Single phase uranium monocarbide was prepared by the solid-solid reaction uranium hydride and carbon above 900°C. At 1, 100°C the reaction completes in 2 hr. The sample form and the graphitization degree of carbon have little effects on the reaction rate. The activation energy of the reaction is estimated to be in the range of 2545 kcal/mol. The rate of the reaction is supposed to depend upon the diffusion of carbon rather than that of uranium.
(2) Uranium sesquicarbide can be prepared by the solid-solid reaction between uranium monocarbide and carbon at 1, 500°1, 700°C. No stress is necessary for its formation. In the preparation of uranium dicarbide, it was found that the temperature highar than 1, 800°C was necessary to prepare it in a pure single phase.
The authors wish to thank Messrs. Toshio Uchijima, Kazuya Takano, Yukio Kawarazaki, Kinji Ouchi and Kunihiro Goto for their assistance in the experiment.
They are grateful to Dr. Masayuki Kawasaki for providing uranium metal, to Tokai Electrode Mfg. Co. for providing carbon sample and to Nippon Electrode Co. for graphitization service. They are also indebted to Drs. Keichi Oshima, Toshio Nakai and Kenjiro Kimura for their continuous encouragement.

View full abstract

The 10 mC order ¹⁴³Pr was purified by the ion exchange following by the elimination of the most part of cerium as ceric phosphate precipitate. The purity of this source was examined and the yields of radioactive praseodymium were measured during the first precipitation, the reprecipitations and the ion exchange purification. Several remarks to obtain an extremely pure source was mentioned.

View full abstract

Highly radioactive fall-out particles were found throughout Japan, resulting from the series of large scale nuclear test explosions carried out by U.S.S.R. during September and October, 1961. Fig. 1 shows the change of radioactivity in air-borne dusts since the beginning of these explosions and Plates 1 (a)-(h) and Table 1 show autoradiographically the changing aspect of fall-out particles in the atmosphere during this period. Many highly radioactive particles were collected and isolated from among numerous non-radioactive dust particles after elaborate procedures. Photomicrographs of them were taken and are shown in Plates 3-24 and Table 2. Plates designated by (P) were taken focussing at the perimeter of particles, showing the shape of the particle contour clearly, but the front side only vaguely. Plates designated by (F) and (M) were taken in order to show the change in depth of the surface state of particles, focussing at the front side of particles and at the middle part between the front side and the perimeter, respectively. We observed microscopically more than fifty highly radioactive particles. Most of them were quite, or nearly, spherical. There were, however, a few particles which deviated appreciably from sphere, as shown in Plates 13 and 16. The surface of some particles was irregular and creased. Several particles were coated with colorless amorphous materials like frosting, as shown in Plates 10 and 11. These materials were assumed to be non-radioactive because they had the same appearance as that of non-radioactive dust particles which were found numerously in air-borne dusts. Several particles had a few small particles of the same color attached on their surface, as shown in Plates 8-11. Almost all of the particles were yellowish, or reddish brown, however, there were some colorless, golden, or black particles. All the highly radioactive particles that we could isolate from among dust particles seemed to be so hard that only an impact of a needle could not crack them into two or more particles. It was found that radioactivity is roughly proportional to volume, as shown in Fig. 2. It seems that particles of light color have larger specific activity than those of dense color and that their conditions of particle formation were different from each other.

View full abstract

The amine extraction (Amex) process can be used effectively for the extraction and separation of thorium from monazite liquor in which rare earths coexist about 10 times richer than thorium.
The results of batch tests on extraction of thorium with 0.18 M Primene JM-T as a solvent show that nuclear grade thorium can be produced by a proper choice of scrubbing solution if desired.
When 4 stages of scrubbing with 0.014M nitric acid solution are used, the content of rare earths in thorium decreases to less than 12 ppm.

View full abstract

The modified charge spectrometer was designed and constructed, and the apparatus was used for the measurements of charge of mosquite incense aerosol, which was charged by corona discharging. The results for test were successful. The charge was calculated from the results by using several different apprroaches, whose methods were given by Lipscomb, Johnstone, Bonssinesq and the authors. On the other hand, the charge taken by aerosol was theoretically obtained on the assumption that the charging of aerosol was done by combined mechanism of ionic diffusion and bombardment. The theoretical values agreed well with the experimental value calculated by Johnstone's approache. The results showed that the sign of the charge of the aerosol was positive at the condition of positive corona. It was found that the corona discharge voltage decreased from the regular value to a lower value in the presence of aerosol.

View full abstract

The kinetics of β-to-α transformation in nucleation and growth mechanism, and the effect of the conditions of heat treatment on grain size have been studied on the alloys containing from 0.25 to 1.0 a/o Cr. Nearly constant activation energies, which vary from 32 to 38 kcal/g-atom with the content of alloying element, correspond to the temperature regions below the noses of T-T-T diagrams. And more effect of isothermal transformation temperature on grain size was observed in the temperature region above the nose of T-T-T diagram than bellow, but the effect of the content of alloying element is not conspicuous in whole temperature region, so far as nucleation and growth mechanism is concerned. As grain size is, in general, discontinuously increased by martensitic transformation, the lower limit of temperature which produces fine structure in isothermal transformation is correspondence to the upper limit of the beginning of martensitic transformation. Ms (β-to-α) temperatures are determined with alloys containing from 0.25 to 1.0 a/o Cr.

View full abstract

Foil techniques play an important role in the experiment in reactor physics. It is always necessary for reactor physicists to compile the newest information on foil techniques in order to conduct fruitful experiments and to make proper interpretation of the results. Then, we present a short note for the latest papers about the analysis and interpretation of foil data which appeared in journal and so on. Information is included on the thermal neutron flux perturbation by foils, neutron self-shielding effect in resonance foils and effective cadmium cutoff energies. Integral measurements of neutron energy spectra are also discussed with the emphasis on the experience accumulated in Japan.

View full abstract