Search Results

You are looking at 1 - 8 of 8 items for

  • Author or Editor: K. Ko x
  • All content x
Clear All Modify Search

Abstract  

The effects of acids on the removal of impurity from 2N grade silica have been studied using five leaching acids: 0.2 M-oxalic acid (pH 1.5 and 2.5), c-aqua regia, 2.5%—HCl/HF, and 1%—HNO3/HF. The presence of 39 impurities in the 2N grade silica and the reference material (RM, 5N grade silica) were investigated by neutron activation analysis (NAA), X-ray fluorescence (XRF), and inductively coupled plasma mass spectrometry (ICP-MS) methods. Major impurities of the 2N silica were Al, K, Fe, Na, Ti, Ca, Mg and P. The fractions of the eight major impurities were 99.2% and 90.9% of total impurity in the 2N and RM silica, respectively. Among the leaching acids, almost all of the major impurities were removed effectively by the 2.5% HCl/HF leaching acid. All the major impurities, except for phosphorous, as well as 21 minor and trace impurities could be determined by the NAA.

Restricted access

Abstract  

Rapid analysis for 90Sr, 232Th, and 238U in human urine samples collected in a radiation emergency can be developed by co-precipitation with calcium phosphate and separation using a Sr-resin (Eichrom Technologies, Inc.) column. The nuclides were measured by inductively coupled plasma mass spectrometry (ICP-MS) or a low background β-counter. Spike tests yielded a good recovery of above 90%. Fractions of 90Sr and the other nuclides (232Th and 238U) were separated in about 2 hours. It was judged that the developed method would be an effective bioassay method in radiation emergency.

Restricted access

Abstract  

Naturally occurring radionuclides (NORN) such as 40K, 226Ra and 232Th from 44 surface sediment samples collected from four desert regions of Chinese were determined to investigate the regional characteristics of the source areas of Asian dust. The radionuclides for 41 surface sediment samples collected from seven sites of the Keum River area in Korea were also determined to compare the regional characteristics with the Chinese desert area. The specific activities (SA) and the specific activity ratios (SAR) of the radionuclides were investigated for distinguishing the source region of Asian dust. The SA of 226Ra and 232Th as well as the SAR of 226Ra/40K and 232Th/40K were found to be useful to characterize source area and tracing Asian dust.

Restricted access

Abstract  

Pyrolytic decomposition of acetylene over the surface of nickel-, cobalt- and iron-containing ordered mesoporous MCM-41 silicas has been studied. Catalytically active matrices have been prepared by chemisorption of volatile metal acetylacetonate complexes on the silica surface. Reduction of the supported metal-containing compounds was carried out in hydrogen or acetylene atmosphere. Acetylene is used not only as a source of carbon in synthesis of the nanostructures but also as a reagent capable of reducing metal ions in the surface chemical compounds. Formation of carbon nanotubes and nanofibers is shown to depend on the pyrolysis conditions.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: Y. Kawabata, M. Yamamoto, V. Aparin, S. Ko, K. Shiraishi, M. Nagai, and Y. Katayama

Summary  

Water and phosphorous fertilizer samples from Karakalpakstan in the Republic of Uzbekistan were analyzed by inductively coupled plasma mass spectrometry, (ICP-MS) to demonstrate the water quality in drinking water, rivers and canals. Uranium concentrations exceeded the WHO (2004) guideline levels for drinking water at some sampling points. Since uranium can also have a toxic effect on kidneys, the effect of uranium from drinking water on people in these areas is significant. One of the main pollutant sources is the phosphate fertilizer leached from agriculture land.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: K. Shiraishi, S. Ko, T. Ban-nai, H. Arae, K. Ayama, P. Zamostyan, N. Tsigankov, I. Los, and V. Korzun

Abstract  

Daily intakes of 134Cs and 137Cs in Ukrainians were estimated in relation to the health effects on habitants after the Chernobyl accident. Two hundred and sixty-eight diet samples were collected from 25 oblasts (regions) using a duplicate portion method. For Ukrainians, the range and median daily intakes of 137Cs were 0.53–571 and 8.8 Bq per person, respectively. Intakes of 134Cs were also detected in highly 137Cs contaminated areas. Daily intakes of 134Cs were in the range of not detected to 3.6 Bq per person. Using the highest radiocesium intakes, annual effective doses for 134Cs and 137Cs were estimated to be 2.5·10−2 and 2.7 mSv, respectively.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: S. Ko, K. Shiraishi, S. K. Sahoo, K. Ayama, Y. Muramatsu, I. P. Los, V. N. Korzun, N. Y. Tsigankov, and P. V. Zamostyan

Summary  

The concentration of stable iodine and bromine in Ukrainian milk has been determined in relation to the effect of the Chernobyl nuclear power plant accident. The geometric mean of iodine and bromine concentration was 31.0mg/kg and 2.57 mg/kg, respectively. Compared with Japanese milk, it was statistically lower. Bromine concentrations in Ukrainian and Japanese milk were not significantly different. Contribution of milk to daily intake of iodine and bromine in Ukrainian adults has been estimated to 88% and 94%.

Restricted access