The destructive determination method of alpha emitters in various combustible solid materials has been investigated by a combination of acid digestion and coprecipitation with barium sulfate. It was consequently established that the method described in the paper may be applicable to determine alpha activities in the practical wastes.
The coprecipitation behaviour of uranium or thorium with barium sulfate is investigated from the variation of yields with uranium or thorium concentration, acid and acidity, and amount of sodium and/or potassium sulfate. Uranium or thorium in quantities less than 1.5 mg is quantitatively coprecipitated with barium (5.9 mg) sulfate when using an optimum conditions. The chemical form of uranium in barium sulfate precipitates is discussed by determination of mole ratio of potassium to uranium.
Amounts of239Pu in alpha-bearing wastes were determined by -ray measurement using a NaI/Tl/ scintillation detector. The deviations of measurement caused by the nonuniform distribution of239Pu in the wastes and by a volume factor were corrected by rotating and scanning the objects. Contribution from241Am coexisting with239Pu was also corrected by taking into account the difference of the counts between A /356–470 keV/ and B /475–620 keV/ intervals. Attenuation of -ray of239Pu was estimated from the matrix density. Thus the content of239Pu could be determined within an accuracy of about 25% at the 1 mg level in a cardboard carton of 17 1.
Authors:S. Ambe, Y. Ohkubo, M. Iwamoto, and Y. Kobayashi
It was found that not only111mCd but also105Ag and106mAg sublimate at 1050 °C under a reduced pressure from Pd foils irradiated with -particles. The sublimation method has enabled rapid separation of the isotopes and repeated use of valuable Pd foils. Adsorption onte -Fe2O3 and coprecipitation with ferric hydroxide were studied by using radioactive tracers.
Authors:Y. Kobayashi, S. Tokonami, Y. Narazaki, W. Zhuo, and M. Furukawa
Radon measurements were carried out in a Japanese wooden house built on granitic geology, where radon-rich well water is used.
Atmospheric radon concentrations were measured over one year with passive integrated radon monitors. The monitors were distributed
at several locations in the house and were replaced every two months. In order to confirm the diurnal variation and heterogeneous
distribution of radon, short-term measurements were carried out accordingly. Radon, its decay products and terrestrial gamma-radiations
were measured in this survey. From the long-term measurement, the radon concentration in the house ranged from 14 to 184 Bq. m-3with an arithmetic mean of 45 Bq. m-3. A radon concentration of 184 Bq. m-3was observed in the bathroom in spring (March-May) though the radon level was normal in the living room and bedroom. In order
to characterize the house, similar measurements were conducted in several surrounding houses. There was a significant difference
in radon concentration between the investigated houses. There was a spatial distribution of the radon concentration and the
highest value was found in the bathroom. Radon and its decay products concentrations varied with time, which increased from
midnight to morning whereas they decreased during daytime. Although the radon concentration in tap water was 1 Bq. l-1, a high level of 353 Bq. l-1was found in the well water.While well water was being used, the indoor radon concentration near the bathroom increased rapidly
with a maximum value of 964 Bq. m-3. It is clear that the use of well water enhanced the radon level around the bathroom.
Authors:Y. Kobayashi, K. Hirata, Y. Ujihira, and K. Itoh
Diffusion coefficients of positronium (Ps) in polycarbonate (PC) have been determined at temperatures between 20 and 300 K by means of positron lifetime spectroscopy. 2,2-dinitrobiphenyl (DNB) was added to the polymer as a Ps quencher and the diffusion coefficients were determined from measured Ps quenching rate constants, assuming that the reaction between Ps and DNB is completely diffusion-controlled.
Authors:T. Saito, Y. Kobayashi, M. Kubo, and Y. Yamada
For Mössbauer -rays in the in-beam Mössbauer experiments using various beams such as heavy ion, secondary short-lived isotope, and neutron beams, it is important to develop a detector. A parallel-plate avalanche counter (PPAC) is the most suitable gas counter for on-line measurements, because PPAC collects the internal conversion electrons emitted by the Mössbauer effect even under high -background. We evaluated the influences of the pressure and flow rate of the counter gas against the counting efficiency of PPAC, and determined the optimum conditions for use in the in-beam Mössbauer experiments.
Authors:T. Kimura, H. Gotoh, Y. Kobayashi, and J. Akatsu
A non-destructive method for determining the amount of actinoids has been developed. The method is based on thermal neutron coincidence counting and employs a selective detection of neutrons resulting from the spontaneous fission of actinoids. The detection system is described in detail and the measurement results of244Cm as an example are presented. The results show that the measured fission rate of244Cm is consistent with the fission rate calculated from ENDF/B-V data and that the amount of244Cm can be determined within about 5% accuracy even in the presence of a large amount of actinoids, for example, up to 2.6·106, 3.6·104, or 1.6·103 times in the mass ratio of239Pu,241Am, or240Pu to244Cm, respectively.
Authors:Y. Tsujimi, M. Kobayashi, H. Furuta, and T. Yagi
The ultra-slow modes with a relaxation time much longer than 1 ns are discovered by a time-resolved spectroscopy in uniaxial ferroelectric (NH2CH2COOH)3H2SO4 (TGS) and in glass-former HOCH2(CHOH)4CH2OH (D-sorbitol). A mode discovered in TGS is a thermal relaxational mode and is proved to be the physical origin of the central peak found by Brillouin scattering. Two modes are discovered in D-sorbitol. One is a thermal relaxational mode. The other is a mode characterized by the Kohlraush-Williams-Watts function with a relaxation time
R. A remarkable result is that
R indicates a critical behavior not at the liquid-glass transition temperature Tg =–7°C but at the ergodic to nonergodic transition temperature Tc=33°C.