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  • Author or Editor: M. Ebihara x
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Abstract  

Radiochemical neutron activation analysis (RNAA) was applied to geochemical and cosmochemical samples to determine trace amounts of Mo and W. To determine the Mo concentration by NAA accurately, the contribution of the fission products of U should be corrected. For that reason, we developed a simple and effective method, where a contribution of fissiogenic 99Mo was estimated by monitoring the ratio of uranium fission-product 99Mo to 133I. Mo concentrations corrected for fission with the W concentrations were consistent with the literature values, showing that 133I was found to be an effective monitor for fission correction. Detection limits are estimated to be 10 ppb for Mo and W and 30 ppb for U under the present experimental conditions.

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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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Abstract  

We introduce the status of the 300-MeV electron linear accelerator used for radioanalytical studies at Tohoku University. In the accelerator facility, several scientific programs for producing radioactivities and use have been performed in several fields, such as photon activation analysis, study of nuclear phenomena influenced by chemical nature, radioisotope production for trace elements, radiation chemistry and irradiation effects by electrons and photons, radioisotope labeling and its mechanism. We show the outlook of the facility, instrumental developments of a beam-course, an irradiation system and several measurement devices. Further, we display a radioanalytical topic in practice, evaluation of trace amount of potassium in high-purity reagent of Gd2O3 by photon activation analysis.

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Abstract  

Chlorine, bromine and iodine (hereafter, halogens) were detemined for rock samples by radiochemical neutron activation analysis. The powdered samples and reference standards prepared from chemical reagents were simultaneously irradiated for 10 to 30 minutes with or without a cadmium filter in a TRIGA-II reactor at the Institute for Atomic Energy, Rikkyo University. The samples were subjected to radiochemical procedures of halogens immediately after the irradiation. Iodine was firstly precipitated as PdI2, and chlorine and bromine were successively precipitated as Ag-halides at the same time. In this study, geological standard rocks, sedimentary rocks and meteorites were analyzed for trace halogens. In some Antarctic meteorites, iodine contents were observed to be anomalously high. Chlorine contents also are somewhat high. The overabundance of iodine and chlorine must be caused by terrestrial contamination on the Antarctica.

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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  

For the determination of trace Cu, Zn and In in rock samples, a simple and convenient scheme of RNAA is presented. In this scheme, relatively short-lived nuclides,64Cu,69mZn and116mIn are radiochemically purified immediately after the irradiation of samples. Although the sensitivity for Zn and In is lower in this scheme than that in the RNAA using65Zn and114mIn at a higher neutron fluence, the present radiochemical procedures are simpler and were proved to be highly effective for the determination of these elements in most terrestrial igneous rocks and meteorite samples.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: M. Oshima, Y. Toh, Y. Hatsukawa, M. Koizumi, A. Kimura, A. Haraga, M. Ebihara, and K. Sushida

Abstract  

A new radionuclide quantification method is proposed on the basis of multiple gamma-ray detection, which is two or higher fold gamma-ray coincidence method. The coincidence method has so far been used for nuclear structure study. We apply this method for quantification of radioactive nuclei. The advantage of this method consists of high energy resolution and high sensitivity. It is successfully applied to nuclear waste analysis, neutron activation analysis and prompt gamma-ray analysis. The principle of the multiple gamma-ray detection method and future perspectives for an innovative pulsed neutron source and a new detector system will be presented.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: M. Oshima, Y. Toh, A. Kimura, M. Ebihara, Y. Oura, Y. Itoh, H. Sawahata, and M. Matsuo

Abstract  

By combining neutron activation analysis with multiple gamma-ray detection (gamma-gamma coincidence), we have proved better sensitivity and resolution for the trace element analysis than the ordinary single gamma-ray detection method. We now try to apply the multiple gamma-ray detection method to the prompt gamma ray analysis (PGA). We have established a new cold neutron beam line for PGA in Japan Research Reactor, JRR-3M, at Tokai establishment of Japan Atomic Energy Research Institute (JAERI). It consists of a beam shutter, a beam attenuator, a gamma-ray detector array, a sample changer, and a beam stopper. We construct a high-efficiency gamma-ray detector array specially designed for this purpose. Its performance has been evaluated with the Monte Carlo simulation code, GEANT 4.5.0.

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Abstract  

In order to search for isotopic anomalies of U caused by the disintegration of 247Cm in meteorite samples, an analytical scheme for determining 235U/238U ratio for a small amount of uranium (less than 1 ng U) was established. The isotopic ratio of U was determined by double-focusing inductively coupled plasma mass spectrometry (DF-ICP-MS). With a great improvement of chemical procedure for purifying the uranium fraction separated from meteorite samples, a variation in 235U/238U ratios was resolved at an order of ±4‰ for 100 ppt or 200 pg U in solution. For applying the procedure in searching an evidence of 247Cm as an extinct radionuclide in the early solar system, a selective chemical dissolution of constituent minerals of meteorites using EDTA and HCl was introduced and a chemical purification scheme of uranium for ICP-MS was established.

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Abstract  

Chondritic meteorite samples were analyzed nondestructively by photon activation analysis. Powdered samples weighing about 50 mg each were irradiated with photons (-rays) converted from electrons accelerated by a linear electron accelerator at 20 and 30 MeV. With 30-minute and 6-hour irradiations, 11 and 12 elements with duplication of 6 elements could be determined, respectively. Considering that several major elements including Mg, Si and Fe can be determined in addition to Ti, Rb, Sr, Y and Zr, which cannot or hardly be determined by instrumental neutron activation analysis (INAA) with rather high sensitivity, instrumental photon activation analysis is as effective as INAA.

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