A sensitive method for Sr-90 analysis by accelerator mass spectrometry

ABSTRACT

Strontium-90 is one of the most important fission products due to the potential health risks of its uptake and retention in the human body. Conventional analysis techniques involve β counting, which requires ingrowth of ⁹⁰Y over a period of two weeks. Accelerator mass spectrometry (AMS) has the potential to shorten the analysis time while offering a lower limit of detection than β counting. Here, Sr in samples was recovered as SrF₂ to provide sufficient negative ions in the caesium-sputtering ion source. In the sample preparation step, 95–98% of Sr was recovered and 99–100% of Zr removed by ion-exchange separation. Sr recovery was ~30% in the precipitation process, and this can be improved. A maximum 500 nA beam current of SrF₃ ^– ions was obtained from SrF₂ samples mixed with PbF₂. A five-anode gas ionization detector was used to avoid isobaric interference from ⁹⁰Zr. The ⁹⁰Sr/Sr atomic ratio background of ~6 × 10^–13 (~3 mBq ⁹⁰Sr) was comparable with that achieved at other AMS facilities. Good linearity in ⁹⁰Sr/Sr atomic ratios was obtained from 1.75 × 10^–10 to 3.38 × 10^–9. Suitable techniques for sample preparation and measurement were thus achieved for ⁹⁰Sr analysis by AMS.     

Helium bubbles and trace of lithium in B4C control rod pellets used in JOYO experimental fast reactor

B₄C pellets used in the control rod of the experimental fast reactor ‘JOYO’ with different ¹⁰B burnups from lower than 10 × 10²⁰ captures/cm³ to 80 × 10²⁰ captures/cm³ and irradiated at less than 800 °C were examined by transmission electron microscopy (TEM). In a B₄C pellet irradiated in an irradiation capsule of ‘JOYO’ at 800 °C up to 30 × 10²⁰ captures/cm³, intragranular helium bubbles appeared in flat plate-shapes with the plane of the plate parallel to the (111) rhombohedral plane. However, in the other specimens that were taken from an actual control rod, the helium gas formed very tiny spherical intergranular bubbles with a diameter of a few nanometers . These tiny bubbles make wavy arrays roughly parallel to the (111) plane. The B₄C specimens were heated on a TEM in situ heating holder up to 1040 °C for 10 min. Clustering of tiny bubbles was observed, but did not extend to the plate-shaped bubbles. In high burnup specimens, large bubbles/cracks were rarely found along the {100} planes, which may correspond to the amorphous bands caused by the slip. While heating the specimens in TEM over 800 °C, liquid phases of lithium-bearing compoundsappeared on the surface of specimen.     

A Powerful Remote Source of O Atoms for the Removal of Hydrogenated Carbon Deposits

We describe a system to deliver a large flux of O atoms for the removal of hydrogenated carbon films from surfaces in remote areas of tokamaks with carbon divertors. The oxygen plasma is generated via electrode-less radiofrequency discharge in a discharge chamber connected to a remote chamber by a 2 m long complex-shaped glass tube 4 cm in diameter. The density of O atoms in the remote chamber was measured with a nickel catalytic probe and its variation with discharge power obtained. The density was close to the detection limit of the probe (around 1 × 10¹⁹ m^?3) as long as the vacuum system was pumped with a rotary pump at a nominal pumping speed of 80 m³ h^?1. The density increased well over 10²⁰ m^?3 when a Roots pump was added. The effective pumping speed at the current setup was up to 200 m³ h^?1. At such conditions, the maximal O-atom density at 2 m from the source was up to 3 × 10²⁰ m^?3. The density depended on the pressure as well as the discharge power. The behavior of O-atom density far away from the source was explained by gas phase and surface phenomena. The effective pumping speed was found to be of crucial importance. The setup was used for removal of model hydrogenated carbon films. Experiments were performed at sample temperatures up to 600 K and etching rates up to 50 nm/s were obtained. We found that the experimental setup is suitable for removal of hydrogenated atoms on a large scale.     

Atmospheric 85Kr and 133Xe activity concentrations at locations across Japan following the Fukushima Dai-ichi Nuclear Power Plant accident

Atmospheric ⁸⁵Kr and ¹³³Xe activity concentrations were determined from weekly air samples collected at Sapporo, Akita and Chiba, Japan, throughout 2011. The results demonstrated that the Fukushima Dai-ichi Nuclear Power Plant accident in early March 2011 resulted in high ¹³³Xe activity concentrations as well as elevated levels of ⁸⁵Kr activity; there was a striking increase in the concentrations of both isotopes over the week running from 14 to 22 March as the radioactive plume released from the plant was captured. At Chiba, following the accident, the ⁸⁵Kr activity concentration increased from 1.38 to 17.7 Bq/m³, while the ¹³³Xe levels increased from below the minimum detectable concentration (MDC ≤ 1.9 × 10^?3 Bq/m³) to 1.3 × 10³ Bq/m³. Conversely, at Sapporo and Akita, high ⁸⁵Kr activity concentrations were not observed, due to differences in air transportation mechanisms based on wind directions. Duplicate samples were collected at Chiba to allow the simultaneous analyses of ⁸⁵Kr and ¹³³Xe at the Japan Chemical Analysis Center and the Bundesamt für Strahlenschutz in Germany and the results were in good agreement. The external effective radiation doses resulting from ⁸⁵Kr and ¹³³Xe releases following the accident were estimated to be approximately 7.0 × 10^?3 and 1.3 μSv, respectively, based on the activity concentrations of these nuclides from March to June in 2011 at Chiba.     

H310BO3/ZnS(Ag)热中子闪烁体转换屏的涂布法制备及性能研究

本文采用涂布法制备了一系列H₃¹⁰BO₃/ZnS(Ag)闪烁体转换屏样品,对其成分配比进行了优化。结果表明,最佳的H₃¹⁰BO₃/ZnS(Ag)质量比在1∶6~1∶7之间,最佳的黏合剂用量为总质量的25%。利用中子照相设备对转换屏的发光均匀性进行了成像分析,结果显示光输出非常均匀;对楔形镉条进行中子成像,并采用调制传递函数(modulation transfer function,MTF)方法计算了系统分辨率,结果显示,在MTF值为0.1时,对于厚度分别为270(11)、350(14)、404(9)及505(15)μm的转换屏,其相应的系统空间分辨率分别为255.6、315.9、371.0和471.3 μm。     

Recent Results in JT-60 Advanced Experiment JT-60 Team,JAERI (Presented by Naoyuki MIYA)

Major efforts in the recent JT-60 experiments have been concentrated on the improved confinement of plasmas with profile control and on the steady state operation study. Peaked density profiles were produced with the successive pellet injection. The energy confinement time was improved by 40% as large as that with the gas fuelled discharges. The fusion products n _e(0)τET _i(0)reached 1.2 × 10²⁰m^?3·s·keV, which was twice that of gas fuelled discharges. High-β_p, plasmas were obtained in low-I _p discharges with improved confinement and a high ion temperature T _i, (0) of 12 keV. The bootstrap current reached 80% of the total plasma current at β_p=3.2. The new concept of a steady-state tokamak power reactor has been proposed on the basis of this result. The maximum current drive efficiency ηCD of 3.4 × 10₁₉m^?2·MA/MW was obtained in the LH current drive experiments. Helium ash exhaust experiments using He-beam injection into H⁺ plasmas showed promising results for α-particle exhaust in a fusion power reactor.     

Tungsten Blister Formation Kinetic as a Function of Fluence,Ion Energy and Grain Orientation Dependence Under Hydrogen Plasma Environment

This work deals with the formation kinetic of tungsten (W) blisters under smooth plasma conditions, i.e. low hydrogen flux and energy in order to analyze the first stages of their formation. In addition, we focus on determining the W grain orientation where blisters grow preferentially. For this purpose, mirror-polished polycrystalline tungsten samples were exposed to hydrogen plasma under fixed hydrogen flux of 2.2 × 10²⁰ m^?2 s^?1, with a fluence in the range of?~?10²⁴ m^?2, ion energy of?~?20, 120 and 220 eV, and sample surface temperature of?~?500 K. The formation of blisters at the surface was investigated using SEM, AFM and EBSD to determine the size, the distribution and the orientation of grain where blisters are formed, respectively. The critical fluence for initiating blisters was established around 2.3 × 10²⁴ m^?2. The evolution of blister size distribution and density is discussed as function of fluence and ion energy. At lower ion energy, i.e. 20 eV, only nanoblisters (less than 150 nm) are observed whatever the fluence value (1.5 and 2.3 × 10²⁴ m^?2). At higher ion energy i.e. 120 and 220 eV, micrometric (~ few to tens of µm) blisters are observed and their density highly depends on fluence. We show that blisters can also be formed on (001) oriented grains contrarily to previous results from the literature where the (111) orientation seemed more favorable. Such information is of importance for tungsten based fusion tokamak operation and design.     

Recovery of neutron-irradiation-induced defects of Al2O3, Y2O3, and yttrium-aluminum garnet

SiC fiber-reinforced SiC matrix composites (SiC_f/SiC) are considered as one of the candidates for blanket materials in future fusion reactors and as an advanced fuel cladding material for next-generation fission reactors. Generally, the densification of SiC needs sintering additives and oxides such as Al₂O₃, Y₂O₃, and yttrium-aluminum garnet (YAG, Y₃Al₅O₁₂), which are frequently added to SiC. However, the effects of neutron irradiation on sintering additives are still unclear. In this study, we performed the neutron irradiation of Al₂O₃, Y₂O₃, and YAG at fluences up to 2.0–2.5 × 10²⁴ n/m² (E > 0.1 MeV) at 60–90 °C. The isochronal recovery of the macroscopic volume of Al₂O₃ against annealing temperature showed smooth and continuous shrinkage at a temperature of up to 1200 °C, and the volume slightly increased above that temperature. In contrast, the volume of Y₂O₃ showed quick shrinkage at the low temperature range, and slower and smooth recovery was observed up to ～1100 °C. In the case of YAG, the recovery of volume occurred in a step-wise manner at 600–750 °C, and continuous shrinkage occurred at temperatures lower and higher than that temperature range. The activation energies for the macroscopic volume recoveries of three oxides were obtained from the Arrhenius plots of the rate coefficients. Two-stage recovery was observed for Al₂O₃, whereas more complicated recovery processes were suggested for Y₂O₃ and YAG.     

Theoretical study of the adsorption of Cs,Cs+, I,I−, and CsI on C60 fullerene

Theoretical investigation for the adsorption of the cesium atom (Cs), the cesium iodide molecule (CsI), the iodine atom (I), the cesium cation (Cs⁺), and the iodide anion (I^?) onto the surface of a single fullerene molecule (C₆₀) are reported. A hybrid exchange–correlation functional using the Coulomb-attenuating method (CAM-B3LYP) is employed. The adsorption energies, i.e., the opposite of enthalpy change through adsorption, are calculated to be 143, 12, 9, 46, and 49 kJ mol^?1 for Cs, CsI, I, Cs⁺, and I^?, respectively. The equilibrium constant for Cs is calculated to be 7×10³ atm^?1 at the temperature of 1000 K and is seven orders of magnitude higher than that for CsI, indicating that the C₆₀ molecule adsorb the Cs atom highly selectively against the CsI molecule.     

Adsorption of Molybdenum Hexafluoride on Magnesium Difluoride for Uranium Purification in FLUOREX Reprocessing

The nuclear fuel reprocessing method FLUOREX is a hybrid system based on fluoride volatility and using solvent extraction. Spent nuclear fuel is fluorinated, and most of the uranium is recovered as UF₆ gas. UF₆ contains some volatile fission product (FP) fluorides, so we considered their elimination from UF₆ by adsorbing them on fluoride adsorbents. We experimentally examined the adsorption of MoF₆ on MgF₂ adsorbent; MoF₆ is present as a volatile FP fluoride in UF₆ produced by the fluorination of spent nuclear fuel. The adsorption isotherm of MoF₆ adsorption on MgF₂ was obtained at MoF₆ pressures from 10^?4 to 50 kPa. The saturated adsorption amount was 1:3 ± 0:4 mg/m² at MoF₆ pressures from 10^?4 to 1 kPa. At MoF₆ pressure of about 10^?3 kPa, the saturated adsorption amount had no dependence on adsorption temperatures from 398 to 463 K. We deduced that MoF₆ was adsorbed as a monomolecule layer on the MgF₂ surface at MoF₆ pressures from 10^?4 to 1 kPa, and the MoF₆ partial pressure in UF₆ could be decreased below 1 × 10^?4 kPa, which is the specific MoF₆ concentration for the reenrichment process.     

Neutron capture cross section measurements of 151,153Eu using a pair of C6D6 detectors

We have measured the neutron capture cross sections of ¹⁵¹Eu and ¹⁵³Eu by the time-of-flight (TOF) method in the range from 0.005 eV to keV region using the Kyoto University Research Reactor Institute - Linear Accelerator (KURRI-LINAC). We employed a pair of C₆D₆ liquid scintillators for the prompt capture γ-ray measurement. The pulse-height weighting technique was employed to obtain the capture yields from the γ-ray spectra of ^151,153Eu. The obtained thermal cross sections at 0.0253 eV are 9051 ± 683 b for ¹⁵¹Eu and 364 ± 44 b for ¹⁵³Eu, respectively. The resonance integrals have been derived as 3490 ± 162 b for ¹⁵¹Eu and 1538 ± 106 b for ¹⁵³Eu.

The obtained capture cross sections were compared with the previously reported experimental data and the evaluated data. The evaluated data in JENDL-4.0 and JEFF-3.2 show good agreement with the present experiment results of ¹⁵¹Eu, however, the evaluated data in ENDF/B-VII.1 are larger than the present experiment results of ¹⁵¹Eu about 10% to 20% in the energy region from 0.03 to 0.2 eV. For the neutron capture cross sections of ¹⁵³Eu, the evaluated data in ENDF/B-VII.1 and Widder's data are in good agreement with the present results in the energy region below 0.35 eV.     

Oxidation of Uranium Dioxide

The oxidation of UO₂ was studied by thermogravimetry and X-ray diffraction. It was clarified that the thermal history covering the first stage of the oxidation from UO₂ to U₃O UO₇ significantly influenced the rate of the oxidation of the second stage from U₃O₇ to U₃ O₈.

The entire oxidation reaction proceeded in what to all appearances, was a single stage when the specimen temperature was raised rapidly, whereas at slower rates of heating up, two distinct stages of oxidation were observed, separated by an intermediate induction period. These findings suggest the existence of a close connection between the rate of formation of the U₃O₇ phase and the rate of the subsequent oxidation of this phase: A slow formation of U₃O₇ would tend to prolong the induction period preceding the second stage of the oxidation. A similar effect was observed also with annealing of the intermediate U₃O₇ at 200°C: The increase of annealing time prolonged the induction stage.

The rate of the second stage oxidation was fairly well expressed by Johnson & Mehl's equation, log (1/(1-y/)=(1/2.303)kⁿtⁿ . The time exponent n in this equation varied in the range of 1.0~2.5, and the rate constant k of 1.15×10^?4~2.04 ×10^?1 min^?1, depending on the experimental conditions.     

Synthesis and thermal conductivity of Y6UO12

Y₆UO₁₂ was synthesized by solid-state reactions of Y₂O₃ and U₃O₈. The high-density pellet of Y₆UO₁₂ was prepared by the spark plasma sintering followed by heat treatment in air for oxygen supplementation. The thermal conductivity (κ) was evaluated using the laser flash method from room temperature to 1173 K. The κ of Y₆UO₁₂ decreased with increasing temperature in the whole temperature range, indicating that the phonon contribution was predominant. The room temperature κ value of Y₆UO₁₂ was 4.90 Wm^?1K^?1. The magnitude relationship of κ among Y₆UO₁₂, Y₆WO₁₂, and Yb₆WO₁₂, i.e. κ of Yb₆WO₁₂ < κ of Y₆UO₁₂ < κ of Y₆WO₁₂, was discussed based on the general lattice thermal conductivity theory.     

The FeSe2(cr) solubility determined by solubility experiments of Se co-existing with Fe

To determine the equilibrium constant for ferroselite (FeSe₂(cr)) dissolution reaction, FeSe₂(cr) solubility experiments were performed at 298 ± 1 K from both the over- and under-saturation directions with Fe–Se precipitates that were aged at 348 K. X-ray diffraction (XRD) analysis detected only FeSe₂(cr) as the Se solid phase in the equilibrated precipitates. The E_h values of the equilibrated suspensions ranged from ?188.6 to ?4.9 mV vs. standard hydrogen electrode (SHE) and the pH values ranged from 6.00 to 8.76. Based on the available thermodynamic data, Se₄^2? and Fe²⁺ are thermodynamically stable within this E_h–pH range. Agreement between the solubility data obtained from the over- and under-saturation directions lends credence to the attainment of equilibrium at 298 ± 1 K. The thermodynamic interpretations using the specific ion interaction theory (SIT) model showed that E_h values and the concentrations of Se and Fe are well represented by the 2FeSe₂(cr) solubility reaction (2FeSe₂(cr) ? 2Fe²⁺ + Se₄^2? + 2e^?) with log₁₀K^○ = ?17.09 ± 0.28. The obtained log₁₀K^○ value falls within the uncertainty limits of the log₁₀K^○ value calculated from the available thermodynamic data.     

Effect of spring water on the radon concentration in the air at Masutomi spa in Yamanashi Prefecture,Japan

The concentrations of ²²²Rn existing in air have been studied by using a convenient and highly sensitive Pico-rad detector system at Masutomi spa in Yamanashi Prefecture, Japan. The measurements in air were carried out indoors and outdoors during the winter of 2000 and the summers of 1999 and 2005. The concentrations of ²²²Rn in spring water in this region were measured by the liquid scintillation method. The concentrations of natural radionuclides contained in soils surrounding spa areas were also examined by means of the γ-ray energy spectrometry technique using a Ge diode detector to investigate the correlation between the radionuclides contents and ²²²Rn concentrations in air at each point of interest. The atmospheric ²²²Rn concentrations in these areas were high, ranging from 5 Bq/m³ to 2676 Bq/m³. The radon concentration at each hotel was high in the order of the bath room, the dressing room, the lobby, and the outdoor area near the hotel, with averages and standard deviations of the concentration of 441 ± 79 Bq/m³, 351 ± 283 Bq/m³, 121 ± 5 Bq/m³, and 23 ± 1 Bq/m³, respectively. The source of ²²²Rn in the air in the bath room is more likely to be the spring water than the soil. The spring water plays carries the radon to the atmosphere. Our measurements indicated that the ²²²Rn concentration in the air was affected by the ²²²Rn concentration in spring water rather than that in soil.     

Erosion of Pyrolytic Graphite and Ti-doped Graphite due to High Flux Irradiation

The erosion of pyrolytic graphite and titanium doped graphite RG-Ti above 1,780K was investigated by 5keV Ar beam irradiation with the flux from 4x10¹⁹ to 1x10²¹ m^?2·s^?1. The total erosion yields were significantly reduced with the flux. This reduction would be attributed to the reduction of RES (radiation enhanced sublimation) yield, which was observed in the case of isotropic graphite with the flux dependence of RES yield of φ^?0.26 (φ: flux) obtained in our previous work. The yield of pyrolytic graphite was roughly 30% higher than that of isotropic graphite below the flux of 10²⁰ m^?2·s^?1 whereas each yield approached to very close value at the highest flux of 1x10²¹ m^?2·s^?1. This result indicated that the effect of graphite structure on the RES yield, which was apparent in the low flux region, would disappear in the high flux region probably due to the disordering of crystal structure.

In the case of irradiation to RG-Ti at 1,780K, the surface undulations evolved with a mean height of about 3μm at 1.2×10²⁰ m^?2·s^?1, while at higher flux of 8.0×10²⁰ m^?2·s^?1 they were unrecognizable. These phenomena can be explained by the reduction of RES of graphite parts excluding Tic grains.     

Determination of carbon contents in the iron meteorites Toluca and Algarrobo

The nuclear microprobe at the cyclotron of the Vrije Universiteit in Amsterdam, The Netherlands, was employed for a study of the iron meteorites Toluca and Algarrobo. Samples were irradiated with ~ 0.4 nA of 1.4 MeV deuterons. Carbon was detected by measuring the proton spectrum of the ¹²C(d, p)¹³C nuclear reaction. The X-ray spectrum of Fe and Ni was measured simultaneously. Area scans of squares approximately 1 × 1 mm² were made with beam size approximately 20 × 20 μm². Spots chosen for the analysis contained areas of taenite, plessite and martensite surrounded by kamacite. Our area scans show clearly that regions of martensite are more C-rich than those of plessite and taenite with lowest C intensity in kamacite. At this point it is still impossible to determine the C-concentrations absolutely with good precision due to possible C-contamination during the target preparation and/or the C-deposition on the irradiated spot during the measurement.However, minimal concentrations of carbon in plessitic and martensitic areas were calculated assuming that all the C counts in kamacite areas come from contamination and using a Fe-C standard with 0.8% C.Further improvements of the technique are planned, including measuring immediately after polishing samples with Al₂O₃, as well as employing a cold trap inside of the irradiation chamber to reduce carbon deposition during measurement.     

Gadolinium Isotope Separation by Cation Exchange Chromatography

Displacement chromatographies of Gd adsorption band in cation exchange resin were performed to observe the isotope effects in the Gd ion exchange processes involving complex forming reagents. The heavy isotope of ¹⁶⁰Gd was found to be enriched at the front boundary of Gd adsorption band and the lighter isotopes of 1MGd, ¹⁵⁶Gd and ¹⁵⁷Gd were enriched at the rear boundary in both cases of 20.1m elution with EDTA and 14 m elution with malic acid, as predicted in the theoretical relations. Observed separation coefficients are 4.9×10^?5, 4.0×10^?5 and 2.5×10^?5for isotopie pairs of ^{156 160}Gd, ¹⁵⁸Gd and ¹⁶⁰Gd, respectively, in the case of EDTA elution. In the case of malic acid elution, smaller separation coefficients were observed as 1.8×10^?5, 1.6 ⁵O^?5 and 0.92×10^?5 for isotopie pairs of ^{156 160}Gd, ¹⁵⁷Gd and^{158 160} respectively.     

Release of iodine from sintered thoria pellets at low temperatures

Post-irradiation thermal release behaviour of ¹³¹I from low-dose irradiated sintered ThO₂ pellets (~5.5 × 10²⁰ fissions/ m³) of average density 79% and 90% TD has been studied in the temperature range 723–1373 K. The possible mechanism of release has been discussed. The kinetics of burst release have been worked out and presented. The release behaviour of ¹³¹I has also been studied from high-dose irradiated ThO₂ pellets (~1.1 × 10²³ fissions/m³). These have shown an increase in diffusivity.     

Sorption Behavior of Selenium(—II) on Rocks under Reducing Conditions

The sorption of radionuclides on rocks is an important factor for performance assessment of geologic disposal of radioactive wastes. Batch sorption experiments under reducing conditions were carried out to investigate the sorption behavior of selenium onto granodiorite, sandy mudstone, tuffaceous sandstone, and their major constituent minerals and accessory minerals. Rock cores and groundwater employed in the experiments were sampled with special care to avoid exposing the cores and groundwater to air to minimize their oxidation. Selenium was spiked as HSe^? and Se₄ ^2- in the experimental solutions, and reducing conditions were maintained throughout the sorption periods. Distribution coefficients, Kd (m³ kg^?1), were obtained in the ranges of 2.2 × 10^?4 to 4.0 × 10^?3 m³ kg^?1 for granodiorite, 3.3 × 10^?2 to 5.6 × 10^?2 m³ kg^?1 for sandy mudstone, and 2.9 × 10^?2 to 8.2 × 10^?2 m³ kg^?1 for tuffaceous sandstone at pHs 8.5 to 11.5. The dominant sorbent minerals for selenium over a neutral to alkaline pH range were determined to be biotite for the granodiorite samples and pyrite for the sandy mudstone and tuffaceous sandstone samples.