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  • Author or Editor: C. Lee x
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Abstract  

An accurate and reliable analytical technique of uranium isotopes in highly contaminated soil samples was developed and applied to the IAEA reference samples. The conventional TBP method of uranium isotopes is insufficient to completely purify uranium from actinides such as plutonium and americium isotopes in highly contaminated soil samples. For overcoming the demerits of the conventional TBP extraction method, sample materials were decomposed with HNO3 and HF, and uranium isotopes were purified by TBP extraction and anion exchange columns and extraction chromatography. Among the purifying methods of uranium, with a TRU Spec resin column after TBP solvent extraction, uranium was completely separated from the radionuclides in a highly contaminated samples. With the modified TBP extraction method, it was found that the concentrations of uranium isotopes were consistent with the reference values reported by the IAEA.

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Abstract  

The cumulative depositions of137Cs,90Sr and fallout Pu in the volcanic ash soil of Korea were determined. The average accumulated depositions of137Cs,90Sr and fallout Pu in the volcanic soil were much higher than those in other forest sites of Korea. From depth profiles, it was found that137Cs,90Sr and239,240Pu in the volcanic soil are more mobile than those in other forest sites of Korea, and that the downward movement of90Sr is faster than137Cs and239,240Pu. A significant correlation was found between the concentration of137Cs and those of90Sr and239,240Pu. The activity ratios of238Pu/239,240Pu and241Pu/239,240Pu in soils are close to those observed in the cumulative deposit from the global fallout of nuclear weapon testings.

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Abstract  

The concentrations and activity ratios of the radionuclides aroundthe nuclear facilities located in Taejon were determined. The concentrationsand activity ratios of uranium isotopes in the downstream decreased with increasingdistances from the point of discharge and reached the reference value after4 km. The concentrations of uranium isotopes in the brook around LWR fuelfabrication facilities were lower than those in the downstream around HWRand LWR fuel fabrication facilities, while the activity ratios of 234U/238U in the brook were higher than those in the downstream.The concentrations of uranium isotopes in the ground water measured quarterlywere variable depending on the sampling time. The concentrations of the grossalpha of airborne particulates collected around the nuclear facilities werefound to be in the narrow range of 0.02 to 0.10 mBq/m3 with a meanvalue of 0.05 mBq/m 3 . Both the concentrations and activity ratios of 137Cs, 239,240Pu and 90 Sr around the nuclearfacilities were not very different from the worldwide fallout. The concentrationsof uranium isotopes in the soil samples around the nuclear facilities werevery close to natural background levels.

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Abstract  

Wastes containing radioactive materials have been produced ever since ore recovery and processing began; however, such materials did not become of public concern until the large-scale activities involving uranium and thorium ores and nuclear fission during and after World War II. Efforts to provide disposal sites for radioactive wastes, especially those associated with nuclear weapons and nuclear energy, have been largely unsuccessful for the past 40 years or so and are nearing crisis proportions as the new millennium begins — its eventual resolution is believed to require greater reliance on stewardship and a larger governmental presence.

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Abstract  

Rapid, in situ measurements were used for quantitative monitoring of gaseous fission products around the nuclear power stations in Taiwan. A portable high-resolution germanium detector with portable multichannel analyzer was used in the field monitoring work. The detecting unit was calibrated using activated Ar, Kr, and Xe isotopes dispersed in a large chamber to obtain absolute efficiency curve in terms of γ-counts per m3 versus gamma-ray energy. The calibrated detecting unit was brought to the nuclear power plants for in situ monitoring for both normal operation and nuclear accidental exercise. In a typical four-hour measurement, the detection limits for most Kr and Xe fission product isotopes were 0.0028%≈0.98% of the derived air concentration (DAC) imposed by the local authority. The dose rate caused by gaseous radioisotopes released from nuclear power stations and dispersed to the surroundings can be quantitatively monitored in a short period using this portable unit.

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Abstract  

Depth distribution of239,240Pu and137Cs in the soils of South Korea have been studied. The average accumulated depositions were estimated roughly to be 54.8±32.1 Bq·m–2 for239,240Pu, 1.6±1.0 Bq· ·m–2 for238Pu and 1982.8±929.1 Bq·m–2 for137Cs. The activity ratios of239,240Pu/137Cs in soils were found to be in the narrow range of 0.0153 to 0.0364 with a mean value of 0.0230±0.006. The concentrations of239,240Pu and137Cs in soils decrease exponentially with increasing the soil depth. A significant correlation was found between the concentration of239,240Pu and that of137Cs. The activity ratios of239,240Pu/137Cs tend to increase slightly with increasing soil depth.

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Abstract  

High resolution inductively coupled plasma mass spectrometry coupled with an on-line flow injection system (FI-HR-ICP-MS) was applied to determine the ultra-trace level 99Tc in soil. The flow injection system (PrepLab) was composed of two TEVA-SpecÒresins, reduced remarkably the sample amounts and the analysis time, compared to the conventional analytical methods. In the flow injection system, Mo and Ru were sufficiently eliminated by using the flow injection system, with the decontamination factors of 1.6.104 and 9.9.105, respectively. With the present method, it was possible to determine ultra-low level of 99Tc in 3-6 g soil at 3–5 hours of analysis time per sample. The relative standard deviation for each sample was less than 4%. The detection limits for 99Tc was 85 fg.ml–1 (0.05 mBq.ml–1), which was calculated from the three times standard deviation of the count rate of the blank.

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Abstract  

This work presents a low-level background gamma spectrometry system capable of achieving rapid determination of90Sr without chemical separation, in a soil sample when the90Sr to -ray emitting nuclide concentration ratio exceeds 10. The system consists of a highly efficient HPGe central detector operated in coincidence or anticoincidence with a NaI(Tl) guard detector and a NaI(Tl) backscatter detector. Experimental results indicate that the bremstrahlung radiation from a pure -emitter can be distinguished with respect to the differences in normal and coincidence spectra. The90Sr activity can be directly detemined in the sample in less than 1 hour with a minimum detectable concentration (MDC) estimated at 0.002 Bq·g–1 for a sample containing no appreciable -ray nuclides or other high energy, -emitting nuclides. In actual measurement, a 0.06 Bq·g–1 MDC for contaminated soils is achieved.

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To investigate the pathogens that racing pigeons in Taiwan are exposed to, a total of 3764 pigeons from 90 lofts were analysed by collection of blood samples in the period between October 2000 and September 2001. The haemagglutination inhibition (HI) test was performed to detect antibodies against Newcastle disease virus (NDV), type 2 avian paramyxovirus (APMV-2), and egg drop syndrome '76 virus (EDS-76V). The agar-gel precipitin (AGP) test was used to detect antibodies against fowl adenovirus (FAV), goose parvovirus (GPV), and avian reovirus (REO). The virus neutralisation (VN) test was applied to detect antibodies against the serotypes FAV-1 and FAV-8. A rapid serum agglutination test was applied for the detection of antibodies against Mycoplasma spp. Antibodies to several infectious agents were found, including NDV (43.3%), EDS-76V (19.2%), FAV (0.8%), REO (0.5%), APMV-2 (0.2%), Mycoplasma columbinum (10.3%), M. columborale (7.1%), M. synoviae (1.8%) and M. gallisepticum (1.3%). Antibodies against GPV, FAV-1, and FAV-8 were not detected in any serum sample. NDV seroprevalence was significantly higher in pigeons of more than one year of age than in pigeons younger than one year. ND or EDS-76 seroprevalence of pigeons vaccinated with ND vaccine or EDS-76 vaccine was significantly higher than that of pigeons that did not receive any vaccination.

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Abstract  

A (D3C)2O (d6-acetone) target was irradiated with semi-monoenergetic neutrons generated from 9Be(p,n)9B reaction with 20 MeV protons to convert 13C and oxygen nuclides in the target into 14C. With both liquid scintillation counting (LSC) and accelerator mass spectrometry (AMS) we measured the (D3C)2O (d6-acetone) liquid targets, which were combustible and easy to afford CO2 for the AMS measurements. The 14C yield measured by the LSC method turned out to be 80 times larger than that by the AMS method. This large discrepancy may be attributed to the loss of 14C atoms during the sample pretreatment in the AMS method such as combustion and cryogenic trapping of CO2. It means that 14C newly produced by nuclear reactions can exist in various chemical forms, i.e., C3D6O, CO, CO2, hydrocarbons, etc., and a simple sample pretreatment right after production can cause serious isotopic fractionation. Therefore, using the AMS method, extreme caution in sample pretreatment should be exercised when the 14C yield produced immediately by nuclear reaction is measured.

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