Isotopic concentration of uranium from alpha spectrum of electrodeposited source on 4H-SiC detector at 500 °C

4H-SiC alpha detectors were fabricated with a 21-μm thick depletion depth and were packaged into a stainless-steel casing with a mineral insulation cable and a standard BNC connector. The packaged detectors had a resolution of 0.624% FWHM at 5.486 MeV prior to salt immersion. The detectors were then immersed in a LiCl–KCl–UCl₃ molten salt at 500 °C, from which a thin layer of depleted uranium was electrodeposited onto the detectors. Alpha particle emission spectra were collected from the electrodeposited source. The energy resolution of the surviving detector was 2.29% FWHM at 4.198 MeV and was sufficient to separate the ²³⁴U from ²³⁸U alpha emissions (577 keV difference). The ²³⁴U/²³⁸U activity ratio and the isotopic concentrations of ²³⁴U and ²³⁸U were determined and are representative of the uranium source used in the electrodeposition.

     

Determination of the 238U spontaneous fission decay constant without neutron irradiation

We have developed a methodology for measuring the decay constant of the spontaneous fission of ²³⁸U, l_f, using nuclear particle track detectors where thermal neutron irradiation is unnecessary. This methodology is based on the fact that the radiation damage caused by spontaneous fission of trans-uranium elements bearing a mass number close to 238 are similar to ²³⁸U spontaneous-fission ones. Loading a thick source of uranium (thickness greater than the fission fragment range) with a small amount of a suitable trans-uranium element (for instance, ²⁴²Pu, which presents a spontaneous fission half-life of 6.75^.10¹⁰ y), it is possible to determine the observation efficiency of a particle-track detector for fission fragments. Procedures concerning our thick source manufacture and uniformity tests of the trans-uranium distribution are also presented. These results make it possible for the exposure of thick uranium sources (without trans-uranium element) to lead to a l_f value.     

Growth mechanism of gold particles on Al2O3 substrates

We investigated the growth of small gold particles on thin alumina substrates obtained by oxidation of aluminum. The particles were vapor deposited in vacuum from a Knudsen cell source with a vapor rate of 1·10¹³ cm^?2·s^?1. In our experiments small Au particles on Al₂O₃ were examined by electron microscopy. From electron micrographs we draw a size histogram of Au particles depending on the mean deposit thickness and the deposition rate. For a mean thickness larger than 1.5 nm the particle size distributions show two peaks. The shapes and the positions of these two peaks allow us to determine the particle growth mechanism and to evidence the importance of the liquid-like coalescence resulting of diffusion and collision of the aggregates.     

In situ measurement of transuranics using a calcium fluoride scintillation detection system

A prototype scintillation spectrometer capable of measuring low energy photons from transuranic elements in groundwater has been developed for in situ applications. The detector is a CaF₂ (Eu) crystal enclosed in a stainless steel casing with a 19 mg·cm^-2 stainless steel entrance window. Evaluation of the system was performed in the laboratory by submersing the probe into a number of aqueous solutions containing varying concentrations of ²⁴¹Am in a simulated well environment. Spectra obtained had easily discernible peaks associated with the low energy L X-rays and the 60 keV gamma-ray photopeak of ²⁴¹Am.     

Preparation of high-resolution 238U α-sources by electrodeposition: a comprehensive study

In this paper the source preparation procedures for high-resolution ²³⁸U sources are described and compared. This work was done within collaboration between CIEMAT and IRMM in the frame of MetroFission, a project of the European Metrology Research Programme, in order to determine the alpha-emission probabilities of ²³⁸U. ²³⁸U was deposited from organic (iso-propanol) and inorganic-H₂SO₄/(NH₄)₂SO₄, saturated NH₄NO₃-electrolyte solutions on metal backings. The parameters affecting electrodeposition were studied and optimized. The activity distribution of uranium was checked by autoradiography. Results show that the ²³⁸U source quality is significantly better using the saturated NH₄NO₃ than the two other electrolytes. By this method, sources of 18.6–22 mm diameter, 26 μg cm^?2 surface density, ~15–18 keV resolution and a peak to valley ratio higher than 50 could be made. This reconciles the inherently opposing requirements of high resolution and sufficient count rate needed to determine the alpha–emission probabilities accurately.     

Precision and accuracy in the determination of plutionium-239 /uranium-233, americium-241/ uranium-233 and curium-244 /uranium-233 alpha activity ratios by alpha spectrometry

Determination of²³⁹Pu/²³³U,²⁴¹Am/²³³U and²⁴⁴Cm/²³³U alpha activity ratios is required when using²³³U as a tracer for the determination of plutonium, americium and curium by alpha spectrometry. Precision and accuracy in the determination of these alpha activity ratios was evaluated by preparing synthetic mixtures from solutions of enriched isotopes of²³⁹Pu,²⁴¹Am,²⁴⁴Cm and²³³U. Separate synthetic mixtures were prepared for each of the three alpha activity ratios. The sources from the synthetic mixtures were prepared by direct evaporation method using tetra ethylene glycol /TEG/ as a spreading agent, alpha spectra were recorded by employing solid state silicon surface barrier detectors coupled to a 4 K analyzer and the alpha spectra were evaluated by a method based on the geometric progression decrease for the far tail of the spectrum. Large area detector /i.e. 450 mm²/ was observed to reduce the effect of nonhomogeneous distribution, if any, of the two elements present in the source. Precision and accuracy of about 1% is demonstrated for the determination of²³⁹Pu/²³³U,²⁴¹Am/²³³U and²⁴⁴Cm/²³³U alpha activity ratios using large area silicon surface barrier detector.     

Spontaneous-fission decay constant of 238U measured by nuclear track techniques without neutron irradiation

A value of the decay constant for spontaneous fission of ²³⁸U, l_f, determined by particle-track detector techniques, is presented. The main source of systematic error in fission-track measurements of l_f, the so called neutron dosimetry, has been avoided. Instead of calibrating the neutron source and the usual mica detector through tracks of ²³⁵U fission induced by thermal neutrons, spontaneous-fission tracks and alpha-particle tracks of ²³⁸U and ²⁴²Pu were used. A value of l_f = (8.66±0.38)·10^-17 y^-1 has been obtained.     

Compact plasma source for removal of hydrocarbons for surface analysis

A low–energy, constricted‐anode Anders‐type plasma source was built and tested for the chemical removal of adventitious carbon on surfaces. Oxygen plasma, generated in the source, extends to the sample surface through an aperture in the anode. This plasma reacts with surface hydrocarbons and removes them in less than a minute without influencing the intrinsic surface stoichiometry of nonoxidizing samples such as minerals, glasses, and metal oxides. Adventitious carbon removal is critical for accurate binding energy determination and quantitative measurements in XPS and AES, particularly in multicomponent materials. We measure the plasma to be composed primarily of O⁺ and O₂⁺, with minor H⁺, H₂⁺, and O⁺⁺ components. Ion energy distributions were measured for O⁺ and O⁺⁺ and show all emitted ions have energies less than 50 eV, confirming chemical desorption as the primary removal mechanism. The plasma source, easily built ‘in house’, is compact and can be mounted on a 2.75‐in flange for in situ specimen cleaning prior to surface analysis. Copyright © 2009 John Wiley & Sons, Ltd.     

Formation of236Pu,237Pu and238Pu isotopes by3He-induced nuclear reactions on uranium

The reaction U(³He, xn)Pu was studied by irradiating enriched²³⁵U (50.3%) and enriched²³⁸U (99.7%) targets with³He ions at the Åbo Akademi cyclotron (Turku, Finland). The incident³He ion energy in the irradiations was 27.0, 24.5 and 21.9 MeV. Plutonium was separated from the thin uranium targets by ion exchange. From the ion exchange fractions obtained, plutonium was electrodeposited on steel plates for alpha and X-ray counting. The activity of²³⁷Pu in the steel plates was determined with a Ge(Li) detector and the activity of²³⁶Pu and²³⁸Pu with a Si surface barrier detector. The cross sections of the reactions and the yields of plutonium isotopes are given.     

锰源对燃烧法制备5V级正极材料LiNi0.5Mn1.5O4的影响

以硝酸锰和醋酸锰,采用蔗糖燃烧法制备锂离子电池正极材料LiNi0.5Mn1.5O4通过XRD、SEM、粒径分布测试、循环伏安、恒流充放电测试以及交流阻抗等方法,研究了醋酸锰和硝酸锰对产物的结构、形貌、粒径及电化学性能的影响。XRD测试结果表明样品的结构都为立方尖晶石型,属于Fd3m空间群。不同的锰源对材料的粒径及粒径分布有很大的影响。以醋酸锰为原料制得的材料的粒径较小并且分布更均匀,有利于锂离子的脱出和嵌入从而提高电化学性能。以醋酸锰为锰源制得的LiNi0.5Mn1.5O4在3.6~5.2 V的充放电电压范围内的电化学性能更好,1C(1C=140.0 mA.g-1)倍率的首次放电容量为144.5 mAh.g-1,循环100周后容量保持率为96%,在3C,5C,10C以及20C的放电容量分别为136.3,132.0,124.7以及96.6 mAh.g-1。     

Characterization of a distributed plasma ionization source (DPIS) for ion mobility spectrometry and mass spectrometry

A recently developed atmospheric pressure ionization source, a distributed plasma ionization source (DPIS), was characterized and compared to commonly used atmospheric pressure ionization sources with both mass spectrometry (MS) and ion mobility spectrometry (IMS). The source consisted of two electrodes of different sizes separated by a thin dielectric. Application of a high RF voltage across the electrodes generated plasma in air yielding both positive and negative ions. These reactant ions subsequently ionized the analyte vapors. The reactant ions generated were similar to those created in a conventional point-to-plane corona discharge ion source. The positive reactant ions generated by the source were mass identified as being solvated protons of general formula (H₂O)_nH⁺ with (H₂O)₂H⁺ as the most abundant reactant ion. The negative reactant ions produced were mass identified primarily as CO₃⁻, NO₃⁻, NO₂⁻, O₃⁻ and O₂⁻ of various relative intensities. The predominant ion and relative ion ratios varied depending upon source construction and supporting gas flow rates. A few compounds including drugs, explosives and amines were selected to evaluate the new ionization source. The source was operated continuously for 3 months and although surface deterioration was observed visually, the source continued to produce ions at a rate similar that of the initial conditions.     

Analytical investigation of energy spectrums of beta rays emitted from <Superscript>90</Superscript>Sr and <Superscript>204</Superscript>Tl radioisotopes

The energy spectra of beta rays emitted from ⁹⁰Sr and ²⁰⁴Tl radioisotopes were obtained by using a silicon surface barrier detector with a 1000 μm depleted layer and 50 mm² effective area. The detector response function is interpreted by making use of range distributions of mono-energetic electrons in matter and by assuming a linear energy loss along the range in the depleted layer of the detector. An analytical expression is given for pulse height distribution obtained in the surface barrier detector. A good agreement is observed between the experimental results and theoretical interpretation.     

Impact of titanium precursors on formation and electrochemical properties of Li4Ti5O12 anode materials for lithium-ion batteries

This work describes comparative study on the application of Li₄Ti₅O₁₂ (LTO) as anode materials for lithium-ion batteries which were successfully prepared by sol-gel synthesis with the use of two titanium sources. One of them was anatase-type titanium dioxide (TiO₂), whereas the second was tetrabutyl titanate (TBT). Both obtained LTO materials were very similar in terms of their crystallinity and purity. In turn, the sample synthetized with TBT source revealed better particle dispersibility, and its particles were slightly lower in size. These particular features resulted in higher Li⁺ diffusion coefficient and better kinetic of Li⁺ ions during charge transfer reactions for the LTO synthetized with TBT source. This reflected in specific capacitance values for both electrodes which equalled 150 mAh g⁻¹, 120 mAh g⁻¹, and 63 mAh g⁻¹ for TBT-LTO and 120 mAh g⁻¹, 80 mAh g⁻¹, and 58 mAh g⁻¹ for TiO₂-LTO at C-rates of 1, 5, and 10 C, respectively.

     

Micro-electrodeposition techniques for the preparation of small actinide counting sources for ultra-high resolution alpha spectrometry by microcalorimetry

Special considerations and techniques are desired for the preparation of small actinide counting sources. Counting sources have been prepared on metal disk substrates (planchets) with an active area of only 0.079 mm². This represents a 93.75% reduction in deposition area from standard electrodeposition methods. The actinide distribution upon the smaller planchet must remain thin and uniform to allow alpha particle emissions to escape the counting source with a minimal amount of self-attenuation. This work describes the development of micro-electrodeposition methods and optimization of the technique with respect to deposition time and current density for various planchet sizes.     

Methodology for uranium compounds characterization applied to biomedical monitoring

Chronic exposure to uranium compounds led to the development of a methodology in order to characterize those compounds. This methodology, based on the recommendation of the I.C.R.P,¹ involves three main steps: the measurement of the uranium concentration and the particle size distribution at workstations; the characterization of the industrial compound, i.e. its physico-chemical properties; and the study of in-vitro solubility using chemical and cellular tests. Different methods for uranium analysis are presented. Results and comments on UF₄, UO₃, U₃O₈, UO₂ and U+UO₂ are given.     

Characteristics of formvar films used to prevent alpha-detector contamination

Alpha spectrometry is an extremely useful and sensitive for detection of alpha-emitting nuclides. Contamination of the silicon detectors for low-level alpha spectrometry by recoil nuclides is a serious problem in the measurement of alpha emitters decaying to daughter nuclides with short half-lives. This unwanted contamination leads to decreased measurement sensitivity causing a degradation of the limit of detection. The simplest method to prevent this radioactive contamination of detector is to use a catcher film between the alpha source and the detector. In this work we describe the obtaining of the thin formvar films as stopper foils for recoil nuclei and we investigated the influence of these films on alpha spectrometry parameters, as energy shift (~30 keV) and resolution (~7%). No significant deterioration of the alpha spectrometry parameters was observed when using thin formvar films. Using the ASTAR web databases, which calculate stopping powers for alpha particles, the thickness of formvar films was estimated to be about 5.355 × 10⁻⁵ g/cm². The measurements were performed with an ORTEC SOLOIST alpha spectrometer with PIPS detector.     

Stratospheric chemical ionization mass spectrometry: nitric acid detection by different ion molecule reaction schemes

Detailed height profiles of stratospheric nitric acid mixing ratios have been derived with a baloon borne chemical ionization mass spectrometer by applying several ion molecule reaction schemes, each associated to a specific and selective ion source. These ions (CO₃⁻, Cl_n⁻, CF₃O⁻, and CF₃O⁻H₂O) give rise to specific product ions (mainly CO₃⁻HNO₃, NO₃⁻HCl, NO₃⁻HF, and CF₃O⁻HNO₃) upon reaction with ambient nitric acid molecules. This paper reports on the instrumental details as well as on the results obtained during two balloon flights with the instrument. Within the accuracy of the measurements, the nitric acid height profiles obtained with the three different ion sources are in good agreement with one another as well as with literature data.     

Activities and their relation to cation distribution in NiAl2O4MgAl2O4 spinel solid solutions

The activity of NiAl₂O₄ in NiAl₂O₄MgAl₂O₄ solid solutions has been measured by using a solid oxide galvanic cell of the type, Pt, Ni + NiAl₂O₄ + Al₂O₃(α)/CaOZrO₂/Ni + Ni_xMg_1?xAl₂O₄ + Al₂O₃(α). Pt, in the temperature range 750–1150°C. The activities in the spinel solid solutions show negative deviations from Raoult's law. The cation distribution in the solid solutions has been calculated using site preference energies independent of composition for Ni²⁺, Mg²⁺, and Al³⁺ ions obtained from crystal field theory and measured cation disorder in pure NiAl₂O₄ and MgAl₂O₄, and assumi g ideal mixing of cations on the tetrahedral and octahedral positions. The calculated values correctly predict the decrease in the fraction, α, of Ni²⁺ ions on tetrahedral sites for 1>x>0.25, observed by Porta et al. [J. Solid State Chem.11, 135 (1974)] but do not support their tentative evidence for an increase in α for x < 0.25. The measured excess free energy of mixing can be completely accounted for by using either the calculated or the measured cation distributions. This suggests that the Madelung energy is approximately a linear function of composition in the solid solutions. The composition of NiOMgO solid solutions in equilibrium with NiAl₂O₄MgAl₂O₄ solid solutions has been calculated from the results and information available in literature.     

High Performance Full Sodium‐Ion Cell Based on a Nanostructured Transition Metal Oxide as Negative Electrode

A novel design of a sodium‐ion cell is proposed based on the use of nanocrystalline thin films composed of transition metal oxides. X‐ray diffraction, Raman spectroscopy and electron microscopy were helpful techniques to unveil the microstructural properties of the pristine nanostructured electrodes. Thus, Raman spectroscopy revealed the presence of amorphous NiO, α‐Fe₂O₃ (hematite) and γ‐Fe₂O₃ (maghemite). Also, this technique allowed the calculation of an average particle size of 23.4 Å in the amorphous carbon phase in situ generated on the positive electrode. The full sodium‐ion cell performed with a reversible capacity of 100 mA h g^?1 at C/2 with an output voltage of about 1.8 V, corresponding to a specific energy density of about 180 W h kg^?1. These promising electrochemical performances allow these transition metal thin films obtained by electrochemical deposition to be envisaged as serious competitors for future negative electrodes in sodium‐ion batteries.     

Coulomb explosion dynamics of N2O in intense laser-field: Identification of new two-body and three-body fragmentation pathways

The Coulomb explosion process of N₂O in an intense laser-field (∼5 PW/cm²) has been investigated by the high-resolution time-of-flight (TOF) spectroscopy. Six two-body explosion pathways involving the NO⁺, NO²⁺, N₂ ⁺ molecular ions have been securely identified from the momentum-scaled TOF spectra of the fragment ions. Assuming a linear geometry, three-body explosion pathways were investigated by sequential and concerted explosion models. When the concerted model is adopted, the observed momentum distributions of six atomic ion channels; N⁺, N²⁺, N³⁺, O⁺, O²⁺ and O³⁺, were well fitted using the Gaussian momentum distribution with the optimized bond elongation factor of 2.2(3). From the yields of individual Coulomb explosion pathways determined by the fit, the abundance of the parent ions, N₂O^z+ (z=2–8), prior to the two- body and three-body explosion processes was found to have a smooth distribution with a maximum at z∼3.