Monoenergetic neutron sources below 100 MeV

Monoenergetic neutron sources are essential for fundamental studies in radiobiology and dosimetry, for measurement of cross sections and kerma coefficients, for calibration of detectors, for activation analysis and for fusion research. Monoenergetic neutrons below energies of 20 MeV are most conveniently produced by reactions between the hydrogen isotopes or between protons and ⁷Li. By proper choice of reaction type monoenergetic neutrons up to 20 MeV can be produced with negligible secondary background radiation. These reactions cannot provide monoenergetic beams between about 8 and 14 MeV and in this “gap” region inverse reactions are most favourable. The most practical way of producing quasi-monoenergetic neutron beams in the energy range from 20 to 100 MeV is by the bombardment of light elements with protons. Because of the relative simplicity of manufacturing suitable isotopically-pure targets and the large 0° cross section, the ⁷Li(p,n)⁷Be reaction is a convenient source of quasi-monoenergetic neutrons over this range of energies, although the ⁹Be(p,n)⁹B reaction is also used.     

Extraction of lithium from GSJ rock reference samples and determination of their lithium isotopic compositions

Li was extracted completely from the Geological Survey of Japan (GSJ) rock reference samples by HF-HC1 decomposition and separated from other alkali metal ions by cation exchange chromatography. The degree of Li isotope fractionation during the preparations of samples for mass spectrometry for Li isotopic ratio measurements was, therefore, negligible. The isotopic compositions of Li extracted from the GSJ samples were measured by double-filament surface ionization mass spectrometry. The permil (%.) deviation, δ⁷Li, of the ⁷Li-to-⁶Li ratio of one of the GSJ samples (JR-1) from that of the Li isotope standard, IRM-016, was +3.9%., with a 95% confidence limit of 0.7%. The δ⁷Li values of the 16 GSJ samples varied in the range −2.5 to +6.4%.. These data are probably the first such data obtained for the GSJ rock samples. No clear dependence of the δ⁷Li value on the kind of rock was observed.     

可充电池的磁共振研究

快速增长的对安全能源的需求,促使科研工作者不断探索高能量密度的可充锂离子电池(LIBs)。发展原位表征技术能更好地研究电池工作中的锂离子镶嵌机制和电池失效因素。固体核磁共振(NMR)能有效的测试短程化学环境:通过对~1H、~(6,7)Li、~(11)B、~(13)C、~(17)O、~(19)F、~(23)Na和~(31)P等同位素来探测电池材料的微观结构。除了魔角旋转(MAS)高分辨NMR谱图研究电池材料的精细结构之外,核磁共振还能无损地捕获、研究电池材料在充放电循环中的演化。因此,原位核磁共振NMR及成像(MRI)可拓展到电池充放电循环中的锂离子的动态演化以及锂离子浓度的时空分布信息。互为补充地,电子顺磁共振(EPR)及成像(EPRI)能有效地跟踪和捕获电极过渡金属、阴氧离子(O_2~(n-))的氧化还原过程。这些实时捕获的动态信息能更好地指导电极材料的构效、微观设计和电池组装的改进,最终获得优异的电化学性能。     

Determination of long-lived radionuclides in concrete matrix by laser ablation inductively coupled plasma mass spectrometry

A laser ablation system using a Nd:YAG laser was coupled both to a quadrupole inductively coupled plasma (ICP) mass spectrometer and to a double-focusing sector field ICP mass spectrometer. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was applied for the determination of long-lived radionuclides in a concrete matrix. The investigated samples were two laboratory standards with a concrete matrix, which we doped with different long-lived radionuclides (e.g. ⁹⁹Tc, ²³²Th, ²³³U, ²³⁷Np) from the ng g⁻¹ to μ g⁻¹ concentration range and an undoped concrete material (blank). Detection limits for long-lived radionuclides in the 10 ng g⁻¹ range are reached for LA-ICP-MS using the quadrupole mass spectrometer. With double-focusing sector field ICP-MS, the limits of detection are in general one order of magnitude lower and reach the sub ng g⁻¹ range for ²³³U and ²³⁷Np. A comparison of mass spectrometric results with those of neutron activation analysis on undoped concrete sample indicates that a semiquantitative determination of the concentrations of the minor and trace elements in the concrete matrix is possible with LA-ICP-MS without using a standard reference material.     

Improving boron isotope ratio measurement precision with quadrupole inductively coupled plasma-mass spectrometry

A method was developed to improve the precision of inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) for the determination of boron isotope ratios (¹¹B/¹⁰B) in various environmental materials including seawater. This approach is based on the common analyte internal standardization (CAIS) chemometric algorithm. The sample solution obtained after digestion is spiked with lithium, and both ⁷Li/⁶Li and ¹¹B/¹⁰B values are measured using long-counting periods (20 min). The CAIS algorithm corrects the measured ¹¹B/¹⁰B values for (a) statistical fluctuations resulting from short-term noise; (b) drift in ¹¹B-to-¹⁰B ratio as a result of long-term deviation in instrumental parameters likely to occur during long counting times; (c) change in ¹¹B-to-¹⁰B ratio caused by variation in matrix elements concentrations; and (d) drift in mass bias correction factor. Comparing boron isotopic ratios in seawater measured by conventional and the new isotope ratio methods validates the procedure. A synthetic isotopic mixture of boron SRM 951 and enriched ¹⁰B SRM 952 also was examined. The CAIS method provided a measured boron isotopic ratio precision of 0.05% R.S.D. while eliminating 5.1% matrix concentration error and 0.25% instrumental drift error.     

高氯酸锂与4-叔丁基苯并-15-冠-5配合物的远红外位移

冠醚化合物对金属离子具有特定的络合作用 [1,2 ] .在冠醚萃取分离锂同位素过程中 ,4-叔丁基苯并 -1 5 -冠 -5 (4 -t-BB1 5 C5 )是锂同位素效应较大且最接近实用的多醚之一 .它容易合成[3] ,而且已有若干萃取研究[4～ 6 ] .本文合成了高氯酸锂与 4-叔丁基苯并 -1 5 -冠 -5配合物 ,测定了若干表征值和远红外位移 ,并根据已有的理论框架[7] 算得配合物的相对约化配分函数比 [(s/s′) f ]org和碘苯 -水溶液两相平衡过程中锂同位素分离系数 α.为在冠醚体系的锂同位素分离研究中应用红外光谱取代质谱 ,直接测定和计算(1 +εp)值提供了可能性 .…     

Thermal dehydration in lithium croconate dihydrate (Li2C5O5·2H2O) studied by vibrational and thermoanalytical techniques

This work reports the thermal dehydration of the oxocarbonic salt Li₂C₅O₅·2H₂O studied by IR and Raman spectroscopy, by ex situ and in situ techniques. The loss of the crystallization water is not only reflected by the disappearing of the pertinent bands, but also by the change in the crystalline phase, as evidenced by the alteration in the splitting pattern of the oxocarbon modes and by differential scanning calorimetry. In the anhydrous salt spectra, a great number of overtones and combination bands appear in the 2000–4000 cm⁻¹ region, indicating an increased anharmonicity. The enhanced splitting suggests that the anhydrous phase belongs to a less symmetric unit cell. The tetrahedral environment around the lithium ion is preserved, as suggested by the shifts of some modes in the 300–600 cm⁻¹ region on isotopic substitution from ⁷Li to ⁶Li. Raman and thermoanalytical data seem to indicate that the crystallization water is released in a single-step process.     

Cyanocuprates as Homo-dimer in Etheral Solution:1H,6Li and 1H,1H Distances Information by NMR

Despite of the wide application of organocuprates in many areas of organic synthesis, little is known about their detailed structures in solution. Recently we found by NMR that organocuprates in etheral solution exist as an equilibrium between solvent separated ion pairs (SSIPs) and contact ion pairs (CIPs) with the preference of the equilibrium mainly dependent of the solvent properties, and the CIPs as the reactive species. We focus here on ¹H, ⁶Li and ¹H, ¹H distances investigation by NMR spectroscopy of Me₂CuLi(l) and Me₂CuLi*LiCN (1*LiCN) in Et₂O as models for the structure of salt-free and salt-containing CIPs in solution.     

Determination of picogram amounts of technetium in environmental samples by neutron activation analysis

A procedure for the determination of trace amounts of ⁹⁹Tc in filter paper and vegetation samples by neutron activation analysis has been developed. The procedure consists of the following major steps: (a) pre-irradiation separation of technetium from the sample and purification of the technetium fraction; (b) thermal neutron irradiation of the ⁹⁹Tc fraction to produce ¹⁰⁰Tc ; (c) post-irradiation separation and purification of ¹⁰⁰Tc from other activated nuclides: (d) counting of the 16-sec ¹⁰⁰Tc in a low-background β-counter.

The estimated detection limits for ⁹⁹Tc by this procedure with irradiations at a thermal neutron flux of about 5.10¹³ n cm^-2 sec^-1 are: 5.lO^-12g ⁹⁹Tc in filter paper samples, and 9. 10^-12 g ⁹⁹Tc in vegetation samples.     

高压离子交换排代法富集锂同位素(Ⅱ)——HETP计算和富集条件

本文根据“精馏平衡塔板型”富集同位素理论提出了富集同位素时计算HETP的方法,寻找出富集和实验参数之间的关系,并进行了讨论;表明Glueckanf塔板理论和Snyder公式适用于简单排代机制的轻同位素富集过程。     

Time-selected spectra in Fourier transform spectrometry of pulsed sources

Time-selected spectra are obtained by electrical switching of a PMT which detects the light emitted by a pulsed source slaved to a high-resolution FT spectrometer. The technique is illustrated by showing strong enhancement of the B ²Σ⁺−X ²Σ⁺ molecular LaO emission relative to Ar lines in a composite wall hollow-cathode pulsed discharge.     

Fourier transform microwave spectroscopic investigation of a very weakly bound ternary complex: OCS–He2

The rotational spectra of the van der Waals complex of carbonyl sulfide loosely bound to two helium atoms were investigated using a cavity Fourier transform microwave spectrometer and a microwave–microwave double resonance spectrometer. The lowest rotational transitions of seven isotopomers, namely those containing the ¹⁶O¹²C³²S, ¹⁶O¹²C³⁴S, ¹⁶O¹³C³²S, ¹⁶O¹²C³³S, ¹⁸O¹³C³²S, ¹⁶O¹³C³⁴S, and ¹⁷O¹³C³²S subunits, were studied. Hyperfine structures due to the quadrupolar ³³S and ¹⁷O nuclei were also observed and analyzed. The search for higher J transitions was not successful and possible causes are discussed. Information about the OCS–He₂ cluster inferred from the measurements is presented and discussed.     

Phase behaviour of lithium and sodium salts of phenylstearic acid

Phenylstearic acid, prepared from oleic acid and benzene, using the Friedel-Crafts reaction, has been confirmed to be a reproducible mixture of twelve positional isomers. Lithium and sodium salts of this acid are semi-crystalline solids which behave in many ways like pure single substances. The thermotropic polymorphism of these soaps has been studied using DSC and polarizing microscopy (as well as X-ray diffraction and ⁷Li NMR spectroscopy for the former soap). Both soaps exhibit characteristic stepwise melting behaviour and form stable reversed hexagonal mesophases at elevated temperatures, in contrast to the lamellar phases exhibited by the unsubstituted soaps.     

Determination of picogram amounts of 99tc by neutron activation analysis

A post-irradiation procedure for the determination of picogram amounts of ⁹⁹Tc in triply distilled water is described. The ⁹⁹Tc is irradiated in a thermal neutron flux of about 5.10¹³ n cm^-2 sec^-l to produce 16-sec ¹⁰⁰Tc. The chemical purification of the ¹⁰⁰Tc from other radionuclides requires 40–45 sec and the technetium yield is about 53%. The purified ¹⁰⁰Tc is counted in a low-background β-counter.     

Automatic scanning of chromatograms by multi-scaling with a gamma-ray spectrometer

The location of gamma-emitting isotopes on Chromatographic thin layers is achieved, together with qualitative and quantitative analysis, by using only a gamma-ray spectrometer. This technique is applied to the determination of the Chromatographic behaviour of nanogram amounts of ⁵¹Cr, ⁵⁴Mn, ⁵⁹Fe, ⁶⁰Co, ⁶⁵Zn and ¹⁰⁹Cd thiocyanate complexes on silica gel. Separations are made of Co, Zn and Cd from Cr, Mn and Fe.     

Liaison hydrogène O-H-O symétrique : II. Spectres de vibration des oxalates acides de lithium hydratés et anhydres

Infrared and Raman spectra of polycrystalline LiHC₂O₄, LiHC₂O₄, · H₂O and their D and ⁶Li containing isotopic derivatives have been investigated at 300 and 90 K in the 4000–50 cm⁻¹ region. All the internal and external optically active modes of lithium hydrogen oxalate monohydrate have been identified and an assignment is given. The spectroscopic data are consistent with X-ray data showing an asymmetric short hydrogen bond with a positive deuterium isotope effect. The dehydration of LiHC₂O₄, · H₂O changes the type of hydrogen bond which becomes symmetric of the double minimum type. The deuteration of LiHC₂O₄, on the other hand. weakens the hydrogen bond and makes it asymmetric again. The asymmetry appears more pronounced at low temperature.     

Platinum determination by instrumental neutron activation analysis with special reference to the spectral interference of Sc-47 on the platinum indicator nuclide Au-199

A method of instrumental neutron activation analysis (INAA) is developed for the determination of platinum by the ¹⁹⁹Au daughter of ¹⁹⁹Pt in the presence of the spectral interference from the ⁴⁷Sc daughter of ⁴⁷Ca. The contributions of the Pt and Ca signals to the integral 157–161 keV peak were separated by calculating the number of disintegrations due to the ⁴⁷Sc from the signal of her parent ⁴⁷Ca at 1297.1 keV γ-ray. The method was used to calculate the trace concentrations of Pt in air samples, collected on filters.     

The South African national Accelerator centre: particle therapy and isotope production programmes

The National Accelerator Centre (NAC) provides facilities for basic and applied research, radioisotope production and particle therapy. To date, 851 patients have been treated on the 66 MeV p + Be isocentric neutron therapy unit while 191 patients have been treated (mainly for intracranial conditions) on the 200 MeV horizontal proton beam facility. A variety of radioisotopes such as ⁶⁷Ga, ⁸¹Rb/⁸¹Kr, ¹¹¹In, ¹²³I, and ²⁰¹Tl are produced on a regular weekly basis, and more than 1000 consignments of radiopharmaceuticals prepared from these radioisotopes are supplied to more than 30 hospitals and private practices throughout South Africa each year. Some non-medical radioisotopes are also produced.     

Packing atomic metal cations with C60: Mass spectrometric observation of M(C60)n with M = Sr and Mo and n = 0–4

The atomic cations of Sr and Mo have been observed to add sequentially up to four molecules of C₆₀ in helium at 0.35 Torr and room temperature in the flow tube of a modified inductively coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. The available center-of-mass energy in collision-induced dissociation experiments of approximately 1.3 eV failed to remove C₆₀ from M⁺(C₆₀)₄. A structure is proposed for M⁺(C₆₀)₄ cations in which the bonding involves η⁶ interaction of the metal with the C₆₀ ligands and η²-to-η² interactions between the C₆₀ ligands.