Search Results

You are looking at 1 - 10 of 10 items for :

  • Author or Editor: K. Yamazaki x
  • Chemistry and Chemical Engineering x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

Since October 1983, the Niigata Prefectural Government has been carrying out the continuous measurements of gamma-emitting radionuclides in the environment around the Kashiwazaki Kariwa nuclear power station by environmental radiation monitoring telemetry system. Continuous measurements of gamma-ray spectra have been established since April 1996. As a result, the contribution of various radionuclides has been gradually clarified in the variations of the gamma-ray dose rate. In this paper, the energy spectrum of the incident gamma-ray to NaI(Tl) scintillation detector was obtained by the unfolding method using a response matrix, and the variations of the energy spectrum observed in the precipitation and snow were investigated. The increase in the dose rate in precipitation originated from the increase in the flux density of gamma-ray from 214Bi and 214Pb, daughter nuclide of 222Rn, which fell down with the precipitation. On the other hand, the reduction in the dose rate in the snowy period was confirmed due to the shielding effect of a part of gamma-rays from the natural radioactive nuclides by the snow layer, in coincidence with the decrease of the flux density in 40K and 208Tl.

Restricted access

Abstract  

Environmental cumulative doses measured by a radiophotoluminescence glass dosimeter (RPLD) and a thermoluminescence dosimeter (TLD) were compared at the same monitoring points during two years. In winter season, when the mean temperature of the monitoring points dropped below 4 °C, the RPLD-sensitivity offered approximately 5% lower values in comparison with those in other seasons. From the artificial irradiation experiments under different room temperatures, the sensitivity of RPLD was found to decrease by 3-4% below 6.3 °C, while the difference was negligible above 8 °C. Based on the present results, much attention should be paid to the sensitivity changes of RPLD, whenever used in cold areas.

Restricted access

Abstract  

Terrestrial zircon and apatite, as examples of uranium rich refractory minerals, and chromite, also highly refractory but uranium poor, were neutron-irradiated for their133Xe release studies. Uranium determination by133Xe was found not to be successful in these refractory samples, due to incomplete fissiogenic-xenon release at 1600°C as revealed by stepwise heating experiment. The high temperature release peaks appeared at ≾1500°C in these terrestrial minerals studied, but at 1000∼1200°C in reported meteoritic whitlockite and chromite.

Restricted access

Abstract  

Uranium concentrations in three types of inclusions of the Allende (C III), a bulk sample of the Plainview (H5), and a bulk and 5 to 15 density separates of the Huckitta pallasite were determined and discussed by comparing the results from homogenized fission track and/or239Np analyses with the133Xe results. Stepwise heating experiment revealed that the133Xe release from the Plainview is bimordal and incomplete by a simple heating at 1600 °C, and that the133Xe releases in the Huckitta bulk and metallic samples are multitudinous but can be extracted rather completely at 1600–1700 °C. In the Huckitta, uranium-rich phase (∼100 ppb) was in the lightest density fraction of d=2.9–3.3, but the bulk uranium was found to be mostly from the heavy metal-rich fraction of d>4.2.

Restricted access

Abstract  

Inductively coupled plasma mass spectrometry (ICP-MS) has been applied to the measurement of plutonium isotopes in soils. In the ICP-MS, a calibration curve method was conveniently utilized even in high viscosity solution using a Babington nebulizer. Plutonium concentrations in soil around the Kashiwazaki-Kariwa nuclear power station were found to be in the range of 0.054 to 1.0 Bq/kg with an average of 0.27 Bq/kg. The ratios of 239Pu/240Pu were also obtained with the ICP-MS to investigate the origin of Pu-isotopes. On the basis of this result, the origin of the Pu-isotopes was attributed to be fallout from the past atmospheric nuclear tests.

Restricted access

Abstract  

Boron concentration of plasma, feces, urine and body tissues from sheep fed with borated water (100 mg B/l) and tap water were determined by neutron-induced prompt gamma-ray analysis to elucidate boron metabolism. The B level in plasma and urine increased rapidly and the B content of feces increased greatly. The B concentrations in body tissues (liver, kidney, spleen, thyroid and muscle) of B dosed sheep were ten times higher than those of tap water administered sheep.

Restricted access

Abstract  

A macroporous silica-based supramolecular recognition absorbent (Calix[4] + Dodecanol)/SiO2–P, was prepared by successive impregnation and fixing the 1,3-[(2,4-diethylheptylethoxy)oxy]-2,4-crown-6-Calix[4]arene (Calix[4]arene-R14) and its molecule modifier 1-Dodecanol onto SiO2 silica-based polymer support. The characterization of (Calix[4] + Dodecanol)/SiO2–P was examined by thermal gravimetry and differential thermal analysis and electron probe microanalysis. Relatively large separation factors of Cs and other metal ions (α Cs/M n+ ) above 60 were obtained in the presence of 3 M HNO3. The adsorption data of Cs(I) fitted well with Langmuir isotherm and the maximum adsorption capacity was estimated to be 0.19 mmol g−1. The Cs(I) in 3 M HNO3 were also effectively adsorption on (Calix[4] + Dodecanol)/SiO2–P in the column operation, and the loaded Cs(I) was successfully eluted with an eluent of H2O. The column packed with (Calix[4] + Dodecanol)/SiO2–P had excellent reusability after three cycles.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: N. K. Labhsetwar, V. Balek, S. Rayalu, T. Terasaka, A. Yamazaki, J. Šubrt, H. Haneda, and T. Mitsuhashi

Summary Studies on ruthenia-titania based materials have been attractive because of their catalytic properties as well as due to the possibility of solid solution formation. Samples of pure ruthenia and ruthenia containing various amounts of titania (10-70 mol%) were investigated during heating of their hydroxide precursors from 20 to 800°C in air using emanation thermal analysis (ETA), thermogravimetry (TG), and differential thermal analysis (DTA). The resulting mixed oxide type materials were characterized by X-ray diffraction (XRD), which indicate the presence of three ruthenia-titania phases. The onset temperature of the crystallization of materials was identified by ETA results, whereas DTA effects characterized the crystallization in bulk of the samples. A good agreement was found between the ETA results and other characterization techniques used. ETA results, indicating the microstructural changes in surface and subsurface of ruthenia-titania based catalytic materials, can be used for optimization of their synthesis protocols to achieve the better physical properties.

Restricted access

Abstract  

In order to know the distribution of plutonium derived from the Nagasaki atomic bomb, soil samples were measured to determine the 240Pu/239Pu isotope ratio of and concentrations of 239+240Pu and 137Cs. The 239+240Pu concentrations in soils, except for Nishiyama area, were close to the average concentration of soil collected in Japan. In soils collected at the Nishiyama area and at the eastern area of Nagasaki Prefecture and at part of northern area in Kumamoto Prefecture, the 240Pu/239Pu ratios were lower than the global fallout values. This suggests that plutonium from the atomic bomb was deposited in the eastern area from the hypocenter reaching up to 100 km eastwards.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: R. Suzuki, T. Ohdaira, K. Yamada, T. Yamazaki, N. Sei, T. Mikado, T. Noguchi, H. Ohgaki, S. Sugiyama, M. Chiwaki, T. Shimizu, M. Kawai, M. Yokoyama, S. Hamada, K. Saeki, N. Nishimura, and T. Tomimasu

Abstract  

A positron lifetime study has been done on dielectric multilayer cavity mirrors for free-electron-laser experiments by the use of a variable-energy pulsed positron beam. A long-lived ortho-positronium component has been observed at low positron energy region, corresponding to the depth of the top amorphous SiO2 layer. The intensity of the positronium component correlates with the degradation and restoration of the mirrors. We discuss the relation between the positronium intensity and degradation mechanism of the mirrors. The present studies revealed that the slow positron lifetime technique is highly sensitive to the properties of the mirrors and is useful for the evaluation of the mirrors.

Restricted access