The design of a spin-polarized slow positron beam

Spin-polarized low-energy positrons were considered as useful probes for studying electron spin states of both surface and bulk materials. Due to the spin-dependent interactions between electrons and positrons, the formation of positronium (Ps), an electron-positron bound system, can be distinguished from different electron spin states. Recently, a positron source of ¹⁸F has been developed for a spin polarized slow positron beam at the institute of physical and chemical research (RIKEN). The design of an electrostatic positron beam will be discussed in conjunction with a spin rotator.     

Capturing aqueous [F]-fluoride with an arylboronic ester for PET: Synthesis and aqueous stability of a fluorescent [F]-labeled aryltrifluoroborate

The aqueous stability of aryltrifluoroborates is of importance to their use in transition metal mediated coupling reactions as well as their potential use in [¹⁸F]-labeled aryltrifluoroborate PET imaging agents. Nevertheless, few studies have fully characterized the solvolysis of fluoride from an aryltrifluoroborate in water. Using [¹⁹F] NMR, fluorescence and [¹⁸F]-labeling techniques, we disclose the composition of an aryltrifluoroborate of exceptional kinetic stability with respect to solvolytic defluoridation. This work not only highlights the potential of using [¹⁸F]-labeled aryltrifluoroborates for PET tracers, but provides a chemical platform and a general approach for evaluating the stability of other aryltrifluoroborates.     

Micro-PIXE and PIGE analysis of individual fluid inclusions

Using the high resolution microprobe which combines PIXE with PIGE measurements, components of trapped fluids can be measured without opening individual inclusions. It is a useful tool for nondestructive all elements' analysis. Micro-PIXE was used to detect the Z> 13 elements and the fluorine concentration was analyzed with micro-PIGE, using the ¹⁹F(p, γ)¹⁶O reaction at 872 keV resonance energy. Primary work of the elemental distributions including light elements in fluid inclusions is also given.     

Vibrational spectra and normal coordinate analysis of two isotopomers of the thiosulfate ion

The Raman spectra of ¹⁸O-thiosulfate ion (S₁O⁻²₃) in H₁¹⁸O solution and the IR spectrum of ¹⁸O-sodium thiosulfate in the solid have been obtained. Normal Coordinate calculations fitting all the fundamental wavenumbers of both ¹⁶O and ¹⁸O isotopomers have been carried out transferring the GVFF of the sulfate ion as the starting point and employing a symmetry force field for the least-squares adjustment procedure. A comparison of the results is made with the known force fields for several sulfur compounds.     

Positronium formation in NaY-zeolites studied by lifetime, positron beam Doppler broadening and 3-gamma detection techniques

Results of positron annihilation measurements on NaY pressed powders and deposited thin films using slow positron beam and conventional fast positron techniques are presented. In lifetime experiments using an external ²²Na source an averaged long lifetime of 1.8 ns with a sum intensity of 27% was observed in pressed powders in the presence of air at room temperature (RT). In literature this lifetime is ascribed to positrons annihilating in water filled or β cages Habrowska, A.M., Popiel, E.S., 1987. Positron annihilation in zeolite 13X. J. Appl. Phys. 62, 2419. By means of isotopic exchange some of the Na was replaced by ²²Na. These powders showed a long lifetime component of 7–8 ns with an intensity increasing from 1 to 12% when heated under normal atmosphere from RT to 200°C. No significant increase of the shorter (1.5 ns) lifetime was observed, while its intensity dropped from 13.4 to 6.6%. Both effects are ascribed to the loss of water from cages only. The beam experiments revealed a high fraction of 3-gamma annihilations in the pressed powder and thin film samples, indicating the annihilation of o-Ps and thereby the existence of large open volumes.     

核药物发展小记

简要回顾了20世纪70年代以来核药物领域发展的主要成就,并对目前在临床上应用最为广泛的核药物探针[18F]FDG作了重点介绍。[18F]FDG的发展可追溯至20世纪20年代,历经半个世纪终于成功应用于临床,在肿瘤、神经退行性疾病、心血管疾病的诊断中发挥了巨大作用。除此以外,本文也介绍了多肽类及蛋白类核药物的最新进展。在梳理核药物发展脉络的同时,本文也借此机会向读者介绍了几位为核药物发展做出巨大贡献的科学家,并作为晚辈向其致以崇高的敬意。最终,笔者希望向读者阐明核药物研究立足基础研究、面向临床问题的学科特色,也希望读者能通过对经典核药物发展脉络的了解,对自身的科学研究有所启发。     

Matrixreaktion von GaF mit o-atomen: ir-spektrum von OGaF

It is possible to synthesize OGaF in an argon matrix by co-condensation of GaF with O atoms. The stretching vibrations of this compound are found at 943 and 690 cm⁻¹ (¹⁶O⁶⁹GaF). An exact calculation of the force field is possible with the aid of the observed ¹⁶O/¹⁸O and ⁶⁹Ga/⁷¹Ga shifts. The following force constants are found: f(GaO) = 6.32; f(GaF) = 4.69; f(GaO/GaF) = −0.1 [10²Nm⁻¹]     

基于稳定同位素的5种蔬菜产地真实性判别

为保护蔬菜产地真实性,以上海市场5种常见蔬菜(生菜、茼蒿、辣椒、番茄和黄瓜)为研究对象,应用单因素方差分析上海和其他产地蔬菜的 δ13 C、δ15 N、δ2 H和 δ18 O值差异,并通过主成分分析(PCA)和偏最小二乘判别分析(PLS-DA)建立上海地产蔬菜真实性判别模型.结果表明,上海地产5种蔬菜总的δ15 N、δ...     

Matrixreaktionen von AlF und AlCl mit o-atomen: IR-spektren von OAlF und OAlCl

It is possible to synthesize OAlF and OAlCl in an argon matrix by co-condensation of AlF and AlCl with oxygen atoms. The stretching vibrations of these compounds are found at 1148 and 740 cm⁻¹ (¹⁶OAlF), respectively 1094 and 490.5 cm⁻¹ (¹⁶OAlCl). As ¹⁶O/¹⁸O isotopic splitting of all frequencies can be observed, an exact calculation of the force constants f(AlF), f(AlO) and f(AlCl) is possible. The force constant f(AlO) is 6.6 [10² Nm⁻¹] for both compounds. This is the first time, that structural data of molecules, containing aluminium with the formal charge 3+ with an AlO bond, have been obtained.     

Efficient regioselective labelling of the CFC alternative 1,1,1,2-tetrafluoroethane (HFC-134a) with fluorine-18

Efficient chemistry is described for the regioselective labelling of the CFC alternative 1,1,1,2-tetrafluoroethane with cyclotron-produced positron-emitting fluorine-18 (t_1/2 = 109.7 min). [1-¹⁸F]1,1,1,2-Tetrafluoroethane was prepared by nucleophilic addition of no-carrier-added [¹⁸F]fluoride to trifluoroethylene and [2-¹⁸F]1,1,1,2-tetrafluoroethane by nucleophilic displacement of tosylate with [¹⁸F]fluoride in 2,2,2-trifluoroethyl p-toluenesulphonate. Each reaction was mediated by a potassium cation-Kryptofix^® 2.2.2 complex, with or without acetonitrile as solvent, in a sealed glassy carbon vessel. The selectivities were 97.2±0.4% for labelling in the 1-position by nucleophilic addition and 91.2±1.2% for labelling in the 2-position by nucleophilic substitution. GC separation afforded each labelled tetrafluoroethane in high radiochemical purity (>99.995%) and high chemical purity (>99.6%). Specific radioactivities of about 37 MBq (1 mCi) per μmol were obtained. Each synthesis was fully automated to cope safely with the high initial radioactivity and delivered purified product within one physical half-life of the fluorine-18 The products are suitable for pharmacokinetic studies in man.     

多巴胺受体显像剂 18F-Fethypride的合成、 放射性标记及生物分布

以香草酸甲酯为原料, 经过7步反应合成了前体化合物(S)-3-[5-{(1-乙基-2-吡咯烷基)甲基胺甲基}-2,3-二甲氧基苯基]丙基-4-甲基苯磺酸酯, 采用NMR和HRMS对其进行了表征; 通过¹⁸F标记合成了新型高亲和力的多巴胺受体显像剂¹⁸F-(S)-N-{(1-乙基2-吡咯烷基)甲基}-3-(3-氟丙基)-4,5-二甲氧基苯甲酰胺(¹⁸F-Fethypride). 该显像剂的合成时间为35 min, 放化产率为(36.8±1.4)%(n=6), 放化纯度经HPLC法检测为99%, TLC法检测为100%, 无菌实验、 鲎试剂检测、 K2.2.2含量检测和急性毒性实验均合格. 纹状体/小脑(Str/Cer)比值90 min达到最高(10.68±0.35), 可作为多巴胺受体显像剂用于诊断神经系统疾病.     

Kinetics of depletion of Co(b F) and Co(a F) atoms by O2

The kinetics of depletion of the lowest two electronically excited states, Co(b ⁴F_J) and Co(a ²F_J), upon interactions with O₂ and N₂ are studied in a fast-flow reactor at a He pressure of 0.70 Torr. The depletion of Co(b ⁴F) or Co(a ²F) by O₂ was efficient. The depletion rate constants were observed to be different among spin-orbit levels within one electronic state. Because reactive channels are not energetically accessible for these two states, the depletion was mostly attributed to electronic energy transfer to vibration or translation of O₂. Efficient depletion upon interaction with O₂ was interpreted through the occurrence of an intermediate formed by the interaction between singly occupied anti-bonding π^* orbital of O₂ and 3d orbitals of Co.     

A density functional theory study applied for carbon and oxygen isotope effects in the system Ni(CO)4/CO

DFT calculations were carried out on the carbon and oxygen isotopomers of CO and Ni(CO)₄ and results compared with (Spindel's) experimental results on the carbon and oxygen isotope exchange equilibria between CO and Ni(CO)₄. The isotopic equilibrium constants, K_B, of carbon and oxygen exchange reactions between CO and Ni(CO)₄ complexes were theoretically calculated as the ratio of the reduced partition function ratios (RPFRs) of the ¹³C/¹²C and ¹⁸O/¹⁶O isotopic pairs for CO and Ni(CO)₄ on the assumption of the internal harmonic vibrations. The agreement between calculated separation factor and Spindel's experimental data are surprisingly good, including the temperature dependence.     

Nuclear motion effects on the C, F and H shielding in methyl fluoride

The ¹⁹F , ¹³C and ¹H shielding in methyl fluoride and its deuterated isotopomers has been calculated from ab initio shielding surfaces for selected temperatures. In each case it is the stretching which contributes most to the nuclear motion corrections which total −9.425 ppm for the ¹⁹F shielding, −4.558 ppm for the ¹³C shielding and −0.601 ppm for the proton shielding. However, some second-order stretching and bending contributions are significant. The deuterium induced isotope shifts are substantial and should be easily measurable. There is a predicted nonadditivity in the ¹⁹F and ¹³C isotope shifts which can be traced to two of the bending contributions.     

Matrixisolation von AsOCl und SbOClMatrix isolation of molecular AsOCl and SbOCl

The molecules AsOCl and SbOCl are formed by reactions of silver with mixtures of AsCl₃ and O₂ or SbCl₃ and O₂ respectively at about 1300 K. After condensation in an argon matrix at 15 K the two stretching vibrations of AsOCl can be observed in the IR spectrum: 984.4 cm⁻¹ [ν(AsO)] and 378.7 cm⁻¹ [ν(AsCl)]. This assignment is confirmed by the measured ¹⁶O/¹⁸O and ³⁵Cl/³⁷Cl isotopic shifts. The calculated AsO force constant shows that there is a real AsO double bond in this molecule.

We failed in the characterisation of SbOCl by the same method, because this molecule is only stable at 1350 K in the presence of gaseous Sb₄O₆ and therefore the absorptions of SbOCl are superimposed by the very strong bands of Sb₄O₆.     

Production of a positron microprobe using a transmission remoderator.

A production method for a positron microprobe using a beta+-decay radioisotope (22Na) source has been investigated. When a magnetically guided positron beam was extracted from the magnetic field, the combination of an extraction coil and a magnetic lens enabled us to focus the positron beam by a factor of 10 and to achieve a high transport efficiency (71%). A 150-nm-thick Ni(100) thin film was mounted at the focal point of the magnetic lens and was used as a remoderator for brightness enhancement in a transmission geometry. The remoderated positrons were accelerated by an electrostatic lens and focused on the target by an objective magnetic lens. As a result, a 4-mm-diameter positron beam could be transformed into a microprobe of 60 microm or less with 4.2% total efficiency. The S parameter profile obtained by a single-line scan of a test specimen coincided well with the defect distribution. This technique for a positron microprobe is available to an accelerator-based high-intensity positron source and allows 3-dimensional vacancy-type defect analysis and a positron source for a transmission positron microscope.     

Orientational properties of liquid-crystalline 4-n-alkyloxybenzilidene-4'-fluoroanilines

The orientational order of 4-n-hexyloxybenzilidene-4'-fluoroaniline, (FAB-OC6) and its 4-n-heptyloxy analogue, (FAB-OC7), studied by means of ²H NMR and ¹⁹F NMR is reported. The entire temperature range of the liquid-crystalline phases (S_B, S_A and N for FAB-OC6, S_B and S_A for FAB-OC7) have been investigated. The results are discussed in relation to previous X-ray diffraction measurements. The chemical shift tensor components of the fluorine bond, evaluated from the ¹⁹F NMR spectra are compared with previous results.     

A concept of a scanning positron microscope

The concept of a scanning positron microscope which is under construction in München and Trento will be shown. A beam with a variable energy from 1 to 30 keV and a spot diameter of 1 m, which can be scanned over an area of (0.6×0.6) mm², is formed after a double stage stochastic cooling of the positrons emitted from a radioactive source. Additionally, the beam will be pulsed to have a well-defined time base for positron lifetime measurements. The design of the microscope is dominated by special demands of positron physics. Therefore, the microscope contains electron optical elements which are well known but rarely used. These are the through the lens reflection remoderator and the optical column with a magnetic side gap lens as probe forming lens.     

SO分子势能曲线及振动能级的从头算研究

用ab initioMRD-CI方法研究了SO分子的基态X³Σ^-及激发态a¹Δ,b¹Σ⁺,A³Π,c¹Π,d¹Σ^-的势能曲线.结果表明,前4个电子态的平衡键长与实验结果吻合得很好,振动能级和转动常数的从头算计算结果也与已观测到的数据较吻合.此外,还对同位素取代物³⁴S¹⁶O和³²S¹⁸O的振动能级和转动常数进行了讨论.     

O/O and H/D separation factors for liquid/vapor permeation of water through an hydrophobic membrane

Liquid/vapor permeation of water through commercial grade hydrophobic PTFE membranes at 323<P(Torr)<160, shows enhancements in logarithmic separation factors, ln[(i'/i)] = In [(χ'/χ) _downstream/ (χ'/χ) _upstream], which differ markedly for isotope separation of oxygen and hydrogen. The prime refers to the lighter isotope and χ is the mole fraction. Thus ln[(16/18)] is found to be as large as 6 times the ratio of the vapor pressure isotope effect, ln(_o = ln (P^o'/P^o), but ln[(H/D)]/ln[_o(H/D)] is only as large as 1.3. The difference in enhancement factors indicates that membrane transport mechanisms must be different for the two separations. The unusually large separation factor for ¹⁶O/¹⁸O may be of practical interest.