Shigekazu Usuda

Efficient isotope ratio analysis of uranium particles in swipe samples by total-reflection X-ray fluorescence spectrometry and secondary ion mass spectrometry

A new particle recovery method and a sensitive screening method were developed for subsequent isotope ratio analysis of uranium particles in safeguards swipe samples. The particles in the swipe sample were recovered onto a carrier by means of vacuum suction-impact collection method. When grease coating was applied to the carrier, the recovery efficiency was improved to 48±9%, which is superior to that of conventionally-used ultrasoneration method. Prior to isotope ratio analysis with secondary ion mass spectrometry (SIMS), total reflection X-ray fluorescence spectrometry (TXRF) was applied to screen the sample for the presence of uranium particles. By the use of Si carriers in TXRF analysis, the detection limit of 22 pg was achieved for uranium. By combining these methods with SIMS, the isotope ratios of 235U/238U for individual uranium particles were efficiently determined.

Application of Fission Track Technique for the Analysis of Individual Particles Containing Uranium in Safeguard Swipe Samples

An effective method for isotope ratio analysis of individual particles containing uranium in safeguard swipe samples was developed by using a fission track (FT) technique combined with thermal ionization mass spectrometry (TIMS). The particles in the sample were directly recovered onto a polycarbonate membrane filter, which was set in a filtration system. After the particle recovery, the filter was dissolved to form a non coated FT detector film containing the particles. Individual particles containing uranium were then identified by the observation of fission tracks created by thermal neutron irradiation. By combining the FT technique with TIMS, isotope ratios of uranium for individual particles in the swipe sample prepared from a uranium standard reference material could be effectively determined.

Phoswich detectors for simultaneous counting of α-, β(γ)-rays and neutrons

Abstract Simultaneous counting of α-, β(including γ)-rays, fast and thermal neutrons was accomplished by devising phoswich detectors with pulse-shape discrimination. The detectors consisted of ZnS(Ag), anthracene and 6 Li-glass (NS8) scintillators: ZnS(Ag)/anthracene phoswich for simultaneous α, β(γ) and fast-neutron counting and ZnS(Ag)/anthracene/NS8 phoswich for simultaneous α, β(γ), fast- and thermal-neutron counting. Satisfactory properties of pulse-shape discrimination among the respective radiations are presented in this paper.

Phoswich detectors combining doubly or triply ZnS(Ag), NE102A, BGO and/or NaI(Tl) scintillators for simultaneous counting of α, β and γ rays

Abstract Phoswich detectors for simultaneous counting of α, β and γ rays have been developed: ZnS(Ag)/Au Mylar/NE102A, ZnS(Ag)/Au Mylar/BGO and ZnS(Ag)/NaI(Tl) for α and β(γ) rays and ZnS(Ag)/Au Mylar/NE102A/BGO and ZnS(Ag)/NE102A/NaI(Tl) for α, β and γ rays. They were prepared by coupling a ZnS(Ag) film scintillator for α counting with a scintillator(s) for β and γ counting having different rise time. In order to adjust each component of pulse height within a given dynamic range, a sheet of Au-coated Mylar (Au Mylar) was used, if necessary, as an optical ND filter for lowering transmittance of scintillation of the ZnS(Ag). Characteristics of these phoswiches were examined by a technique of pulse-shape discrimination. Excellent discrimination among the radiations was attained and small tailings from each other peak were obtained for the prepared phoswiches.

Development of analytical techniques for ultra trace amounts of nuclear materials in environmental samples using ICP-MS for safeguards

The authors have begun to develop analytical techniques for ultra trace amounts of nuclear materials and to prepare a clean chemistry laboratory for environmental sample analyses. The analytical techniques include bulk and particle analyses. For the bulk analysis, concentrations and isotopic ratios of U and/or Pu are determined by inductively-coupled plasma mass spectrometry (ICP-MS) and thermal ionization mass spectrometry (TIMS). In the particle analysis, isotopic ratios of U and/or Pu in each particle will be measured by secondary ion mass spectrometry (SIMS). This paper reports on the outline for the development of analytical techniques and the current situation of the development of the bulk analysis using ICP-MS is described.

Simultaneous counting of α-, β(γ)-rays and thermal neutrons with phoswich detectors consisting of ZnS(Ag), 6Li-glass and/or NE102A scintillators

Abstract Simultaneous counting of α-, β(including γ)-rays and thermal neutrons was realized by combining doubly or triply ZnS(Ag) film, NS8 6 Li glass and/or NE102A plastic scintillators with or without Au Mylar (Au-coated Mylar films). The Au Mylar was used as an optical ND filter to discriminate thermal neutrons detected with the NS8 from α-rays detected with the ZnS(Ag) in pulse height by interposing behind the ZnS(Ag). The other discriminations were achieved by pulse shape analysis. Satisfactory discrimination among α-, β(γ)-rays and thermal neutrons was obtained with the ZnS(Ag)/Au Mylar/NS8 and ZnS(Ag)/NE102A/NS8 phoswiches. Discrimination characteristics of the devised phoswiches were described.

Rise time spectra of α and β(γ) rays from solid and solution sources with several solid scintillators

Abstract By using a simple pulse shape discrimination technique, rise time spectra of α and β(γ) rays from solid sources were measured with several solid scintillators (CsI(Tl), NaI(Tl), CaF 2 (Eu), BaF 2 , BGO − , NE102A and stilbene). The best scintillator among them for resolution between α and β(γ) rays was a CsI(Tl) crystal (a figure of merit: 2.4). After the resistance of thin Au- and Al-coated Mylar films to various solutions was examined, the discrimination between α and β(γ) rays from the solutions was also proved to be feasible by measuring with the CsI(Tl) scintillators protected with the films (a figure of merit: 1.8–2.0).

Flow monitor for actinide solutions by simultaneous α and β(γ) counting using a CsI(Tl) scintillator

Abstract This paper deals with a flow monitor which is capable of continuous determination of α and β(γ) activities in actinide solutions with a CsI(Tl) scintillator protected by Au-coated Mylar films with the aid of pulse shape discrimination. A demonstration of the flow monitoring was made on enriched uranium solutions ranging in concentration from about 0.1 to 100 g/l.

Properties of a YAP powder scintillator as alpha-ray detector

A YAP scintillator (YAlO3: Ce crystal) for alpha counting has been produced in powder form and this paper describes its performance characteristics. By measuring pulse-height and rise-time distributions, it was found that the YAP powder, as a fast detector for alpha rays, could clearly distinguish alpha events from beta and gamma events. In addition, the YAP powder was used in a phoswich detector combined with a YAG (Y3Al5O12: Ce) crystal for beta and gamma detection.

The use of Si carriers for aerosol particle collection and subsequent elemental analysis by total-reflection X-ray fluorescence spectrometry

Abstract The adoption of polished Si carriers was studied for the sensitive elemental analysis of aerosol particles using total-reflection X-ray fluorescence (TXRF) spectrometry. The surface roughness of the Si carrier measured by atomic force microscopy was found to be smaller than those of glassy carbon and quartz glass carriers, which are commonly used for TXRF analysis. The detection limits of elements for the Si carrier were superior to those for the glassy carbon and the quartz glass carriers, presumably due to its smaller surface roughness. For example, the detection limit of Sr for the Si carrier was 9 pg, which was 100 times and 3 times lower than those for the glassy carbon and the quartz glass carriers, respectively. The Si carriers could be successfully applied to the direct aerosol particle collection by impaction and the subsequent elemental analysis by TXRF. From the results of the elemental analysis of aerosol particles, the variations in the concentrations of K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn Sr and Pb with time could be clarified.