Satoshi Sakurai

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.

Improved Method of Fission Track Sample Preparation for Detecting Particles Containing Fissile Materials in Safeguards Environmental Samples

We have developed an effective method for fission track (FT) sample preparation to perform particle analysis of the safeguards environmental samples by the FT-thermal ionization mass spectrometry (TIMS) method. In this method, a FT detector and the layer containing particles are separated. The main feature of the developed FT sample is that the detection of a particle from the corresponding FT can be performed correctly and in a simple manner by fixing each one end of the detector and the particle layer and by using an etching tool. It is expected that this method will enhance the effectiveness of particle analysis.

DEVELOPMENT OF PHOSWICH DETECTORS FOR SIMULTANEOUS COUNTING OF ALPHA PARTICLES AND OTHER RADIATIONS (EMITTED FROM ACTINIDES)

Abstract In order to develop actinide monitors, simultaneous counting of α particles and other radiations has been investigated by means of phoswich detectors. Typical phoswiches devised up to the present consist of the following: ZnS(Ag)/NE102A for α and β(γ) counting, ZnS(Ag)/NaI (Tl) or YAP for α and β(γ) counting, ZnS(Ag)/anthracene/6Li glass for α, β(γ), thermal- and fast-neutron counting, etc. Optical filters could be applied to some of such phoswiches for adjustment of pulse height and/or pulse shape. An attempt to directly detect enriched uranium solution for actinide flow monitoring and proposed future developments are also described.

Challenge to ultra-trace analytical techniques of nuclear materials in environmental samples for safeguards at JAERI: methodologies for physical and chemical form estimation

From a viewpoint of physical and chemical form estimation, ultra-trace analytical techniques of nuclear materials in environmental samples for safeguards have been investigated at Japan Atomic Energy Research Institute. This article deals with (1) an outline of the developed techniques for bulk and particle analyses of uranium and plutonium in the safeguards environmental samples; (2) current R&D on techniques relating to estimation of the physical and chemical form, such as SEM images and EDX spectra for fine particles of nuclear materials and fission track observation applicable to fissile materials; and (3) possible analytical methodologies, as future works, applicable to ultra-trace amounts of nuclear materials in environmental samples.

Isotope Ratio Measurement of Uranium in Safeguards Environmental Samples by Inductively-Coupled Plasma Mass Spectrometry (ICP-MS)

In order to measure isotope ratio of uranium in safeguards environmental samples with ICP-MS precisely, production of polyatomic ions of IrAr, PtAr and AuAr was measured and mass bias of ICP-MS is investigated by using isotopic standards of uranium and lead. The intensities of IrAr, PtAr and AuAr relative to the atomic ions were found to be 1.8×10-6, 1.6×10-5 and 4.1×10-5, respectively. The production of 193Ir40Ar is too small to interfere with the measurement of 233U, if the concentration of Ir is the same level as that of 233U. However, there is possibility that the presence of Pt and Au interferes with the measurement of minor isotopes of uranium and 237Np. On the other hand, the mass biases of 235U/238U and 208Pb/206Pb were measured with the parameter of 238U16O/238U. Since unexpected change of the mass bias during measurements causes frequently erroneous results, the monitoring of 238U16O/238U is effective for the precise isotope ratio measurement.

Simultaneous counting of radiation emitted from actinides with improved phoswich detectors by applying an optical filter

The effects of optical filters on rise times of output signals from a ZnS(Ag) scintillator have been examined, and phoswich detectors applying them were devised for more effective simultaneous counting of α and β (including γ) rays emitted from actinides. The optical sharpcut filters made the rise times slower and optical bandpass filters made them faster. In this paper, two improved phoswich detectors, ZnS(Ag)/sharpcut-filter/NaI(Tl) and ZnS(Ag)/bandpass-filter/CsI(Tl), are demonstrated.

A Screening Method for Uranium Particles in Safeguards Environmental Samples Based on Etching Behavior of Fission Tracks

A screening method for uranium particles according to their enrichment has been developed by using the characteristics of fission tracks, which depend on the enrichment of the uranium particles. A two-step filtration system that can collect particles with desired diameters was used for the collection of uranium particles from a swipe sample in order to avoid the influence of the differences in the diameter on the etching behavior of fission tracks. It was shown that the enrichment-based screening of the uranium particles is possible by controlling the etching time to detect fission tracks and by comparing fission track morphologies.

Adsorbed compounds on pine needle surfaces for the environmental monitoring of uranium

In order to examine the feasibility of the adsorbed compounds on the pine needles for environmental monitoring of uranium, the adsorbed compounds were recovered by solvent washing, and the elemental concentrations in the compounds were compared with those of air particles and pine needles. It was found, that the concentration patterns of elements in the compounds corresponded to those of air particles, which meant that the air particles were the main components of the compounds. The analysis by ICP-MS suggested that the uranium in the compounds has a natural composition. Therefore, the adsorbed compounds to the pine needles can be considered as potential indicators for the environmental monitoring of uranium.