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  • Author or Editor: M. Kobayashi x
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Abstract  

Carrier- and salt-free42K milked from an42Ar–42K generator was utilized for isotope dilution analysis of potassium in ultra-pure water. Potassium in the sample marked with the42K was shown to be concentrated easily 60 times by crown-ether extraction and acid back-extraction to be determined by atomic absorption spectrophotometry. The same extractions proved to be effective for removing the reagent blank. Cerenkov radiation counting was often suitable for42K measurement. The42K was used also for studying the interaction of ultra-low concentrations of potassium with vessel walls.

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Abstract  

We present a brief description of the status of our accelerator mass spectrometry system at the tandem accelerator facility of the University of Tokyo and some examples of measurements in environmental samples which have been recently performed. Fallout10Be activities have been measured, from rain samples collected monthly in Tokyo from 1975 to 1977 and from 1984 to 1986, and compared with those of7Be and137Cs. A preliminary experiment on14C measurement in volcanic gas samples is also reported.

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Abstract  

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 T g =–7°C but at the ergodic to nonergodic transition temperature T c=33°C.

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Abstract  

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.

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Abstract  

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.

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Abstract  

Airborne particulate matter was collected at the intersection of Industrial Road in Kawasaki-city, Kanagawa, Japan using a 12-stage low-pressure impactor. High concentrations of airborne particulate matter have been observed in this area. The collected samples were analyzed for 34 elements by instrumental neutron activation analysis (INAA), and data on the elemental concentrations were obtained. High concentrations of fine particles of As, Br, Sb, V, and Zn were observed. It was further observed that these fine particles were originated predominantly from the wear of tires and brakes, and not from automobile exhaust emissions.

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Abstract  

In order to improve the accuracy of reactor neutron activation analysis, flux gradients and spectrum changes in the irradiation capsule have been studied at the Kyoto University Reactor (KUR). The flux and spectrum monitoring samples of Fe, Co, Au, Sb, U and Ni were placed at several positions in a polyethylene irradiation capsule of 24 mm inner diameter and 98 mm length, and were irradiated in a pneumatic irradiation facility (Pn-2). The flux gradients were found to be rather negligible in the vertical (axial) direction while they were considerable in the radial one. The flux gradient was around 5%/cm for thermal neutrons and 10%/cm for epithermal and fast neutrons. The spectrum changes were dependent on the materials (polyethylene and silica) filled in the capsule. Based on these observations, the effect of the flux gradients and spectrum changes on the accuracy of reactor neutron activation analysis was discussed.

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Abstract  

Chemical compositions of spherules separated from deep sea sediment dredged off Hawaiian islands and from Antarctic ice were measured by instrumental neutron activation analysis (INAA) using Kyoto University Reactor (KUR). Iron, cobalt, nickel, iridium, scandium and manganese contents in those spherules were determined to be 19.3–97.7%, 23–4370 mg·kg−1, 0.08–7.04%, 0.84–35.4 mg·kg−1, 1.4–44.3 mg·kg−1 and 93.4 mg·kg−1–7.2 %, respectively, and compared with each other. Particularly, iridium was detected in seven spherules among fourteen from Hawaii, but only one spherule among twenty-two from Antarctic, and those spherules turned out to be extraterrestrial in origin. However, it was shown that there was little difference in characteristics of elemental contents between both kinds of spherules, except for Ir-detected spherules.

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Abstract  

Chemical composition of 15 magnetic spherules collected from deep sea sediment was determined by instrumental neutron activation analysis (INAA) under two different irradiation conditions using the Kyoto University Reactor (KUR). Based on their chemical composition, nine spherules were judged to be of extraterrestrial origin. The differences in the chemical composition of the nine spherules are discussed in terms of condensation temperatures for the elements. Comparing the detection limits derived from INAA under two different irradiation conditions, the sensitivity for INAA using KUR is discussed.

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Summary  

A simple and reliable sampling system for 3H and 14C in airborne release from nuclear facilities was designed. The sampling system can collect 3H and 14C simultaneously with a condensation technique using a commercially available cold trap equipment and a CO2 absorption technique using an organic alkali monoethanolamine solution, respectively. In situ performance tests for the effluent from a reprocessing plant showed that the system has high and stable efficiencies for collecting 3H and 14C for a one-week batch sampling at a sampling flow rate of 0.4 l . min-1. These collection techniques also provided a simple procedure of following sample preparation for activity measurements by liquid scintillation counting. The detectable concentrations of the proposed monitoring method were 3.0 Bq . m-3 for 3H and 1.6 Bq . m-3 for 14C, respectively. The sensitivity would be on an acceptable level for routine monitoring of airborne release at nuclear facilities.

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