Auswahl der wissenschaftlichen Literatur zum Thema „27Al(d,a)“

The 13C, 27Al and 11B NMR spectra of tri(tert-butyl)alane, AlBut3, and of the corresponding borane, BBut3, respectively, were examined in order to determine the magnitude of the coupling constants 1J(27Al,13C) = 94±5 Hz and 1J(13C,11B) = 52±2 Hz by measurement of the line widths of the 13C NMR signals and of the relaxation rates of the quadrupolar 27Al and 11B nuclei. This is the first example of 1J(27Al,13C) determined for a monomeric trialkylalane. In addition, the coupling constants were calculated by DFT methods (B3LYP) using the 6-311+G(d,p) basis set. The 1H, 13C and 27Al NMR spectra of lithium tetra(tert-butyl)alanate, Li[AlBut4], were measured under various conditions. Ion-pair separation in THF revealed the expected patterns for 27Al-13C spin-spin coupling across one and two bonds as well as for the three-bond 27Al-1H spin-spin coupling.

We report a complete set of high-resolution solid-state NMR spectra for all magnetic nuclei (1H, 13C, 17O, and 27Al) in the α-form of tris(2,4-pentanedionato-O,O′)aluminium(III), α-Al(acac)3. These high-resolution NMR spectra were obtained by using a host of solid-state NMR techniques: standard cross-polarization under the magic-angle spinning (CPMAS) method for 13C, 1-D homonuclear decoupling using the windowed DUMBO sequence for 1H, double-rotation (DOR) for 17O and 27Al, and multiple-quantum MAS for 27Al. Some experiments were performed at multiple magnetic fields. We show that the isotropic chemical shifts obtained for 1H, 13C, 17O, and 27Al nuclei in α-Al(acac)3 are highly resolved and accurate, regardless of the nature of the targeted nuclear spins (i.e., spin-1/2 or quadrupolar) and, as such, can be treated equally in comparison with computational chemical shifts obtained from a gauge-including projector-augmented wave (GIPAW) plane-wave pseudopotential DFT method.

AbstractIntegral cross sections of the reactions 24Mg(n,p)24Na, 27Al(n,p)27Mg, 27Al(n,α)24Na, 58Ni(n,d + np)57Co and 60Ni(n,p)60Co were measured for the first time using the fast neutron spectrum of a TRIGA reactor extending from 0.5 to 20 MeV. The values obtained in this work were comparable with the recommended values for a pure 235U prompt fission spectrum. The measured integral value was utilized for integral test of excitation function of each reaction given in some data libraries, namely ENDF/B-VIII.0, TENDL-2017, IRDFF-1.05 and ROSFOND-2010. The integral measurements are generally consistent with the integrated values within 5 %, except for a few cases, e. g. the reaction 60Ni(n,p)60Co, where the data libraries appear to need improvement.

Cross sections of the 174Hf(n,2n)173Hf and 176Hf(n,2n)175Hf reactions have been experimentally determined relative to the 27Al(n,α)24Na reference reaction at incident neutron energies of 15.3 and 17.1 MeV by means of the activation technique. The irradiations were carried out at the 5 MV tandem T11/25 Accelerator Laboratory of NCSR "Demokritos" with monoenergetic neutron beams provided via the 3H(d,n)4He reaction, using a new Ti-tritiated target of 373 GBq activity. In the determination of the 176Hf(n,2n)175Hf reaction cross section the contamination of the 174Hf(n,γ)175Hf and 177Hf(n,3n)175Hf reactions has been taken into account. Moreover, the neutron beam energy has been studied by means of Monte Carlo simulation codes and the neutron flux has been determined via the 27Al(n,α)24Na reference reaction.

In recent works, many industrial by-products were employed as solid precursors for the synthesis of alkali-activated binders and as alternatives to Portland cement for the immobilization of hazardous, toxic and nuclear wastes. Among industrial wastes, alkali-activated brick was found to be an interesting porous composite for removing very toxic heavy metals (Pb2+, Cd2+, Co2+) and radio-nuclides (Sr2+, Cs+, Rb+) from aqueous solutions. The starting material is very attractive due to the presence of metakaolinite as a geo-polymer precursor and silica for increasing material permeability and facilitating water filtration. The alkaline reaction gave rise to geo-polymerization followed by partial zeolitization. Elemental surface micro-analysis was performed by Scanning Electron Microscopy (SEM) equipped with an Energy-Dispersive X-ray Spectrometer (EDS). The formation of crystalline phases was corroborated by X-ray diffraction (XRD) analysis. Information about 29Si, 27Al and 1H nuclei environments in crystallized and amorphous aluminosilicates was obtained by 29Si, 27Al and 1H MAS NMR. 27Al–1H dipolar-mediated correlations were investigated by employing dipolar hetero-nuclear multiple quantum coherence (D-HMQC) NMR, highlighting Al–O–H bonds in bridging hydroxyl groups (Si–OH–Al) that are at the origin of adsorptive properties. Aqueous structural stability and cationic immobilization characteristics before and after material calcination were investigated from acid-leaching experiments.

The use of deuteron bunches collectively accelerated in a Luce diode to an average energy of 1200±200 keV and a number of 1013 per shot is shown for the radioactive determination of the stoichiometry of AlN coatings with a known thickness. In each shot, the deuteron energy was determined by measuring the drift velocity of the virtual cathode collectively accelerating deuteron bunches, and the coating stoichiometry was determined with an accuracy of no worse than ±5% from the ratio of the activities of the 28Al/15O radionuclides induced in the nuclear reactions 27Al(d,p)28Al and 14N( d,n)15O, respectively.

The oxidation behavior of ion-implanted steel samples in air, using Nuclear Reaction Analysis (NRA) and Rutherford Backscattering Spectroscopy (RBS) techniques. Austenitic stainless steel AISI 321 (Fe/Crl8/Ni8/Mn2/Ti) samples implanted with magnesium-, aluminum- and zirconium-ions (implantation energy 40 keV, dose: 1-1017 to 2-1017 ions/cm2) were oxidized in air in the temperature region 450-650 °C for several periods of time. The above implants were selected on the basis of the affinity to oxygen, as well as their ability to form protective oxides as MgO, AI2O3, Zr02 in order to improve the oxidation resistance of steel. The determination of the oxygen concentration and depth-profiles was performed by means of the 160(d, p)170 nuclear reaction. Rutherford Backscattering Spectroscopy was applied to investigate the near-surface layers and to determine the depth profiles of the implanted ions. The determination of the aluminum concentration and the depth distribution of the Al-ions was performed using the resonance at 992 keV of the 27Al(p, 7)28Si nuclear reaction whereas the concentration and the depth distribution of the Mg-ions by the means of the 24Mg(o;, p)27Al reaction. The excitation function of the 24Mg(a:, p)27Al nuclear reaction was studied in the energy region 4600-5000 keV and absolute cross section data allowing the determination of the Mg-profile were determined for this purpose.

Collective acceleration of protons and deuterons is compared in the same geometry of a Luce diode with a polyethylene anode at an accelerating diode voltage of 250 kV, current and pulse duration of relativistic electrons up to 30 kA and 90 ns, respectively. The accelerated ions were intercepted by B4C, BN, and AlN plates, in which analytical radionuclides were produced according to nuclear reactions 10B( p , α)7Be, 12C( p, γ)13N, 10B( d , n )11C, 12C( d , n )13N, 14N( d , n )15O and 27Al( d , p )28Al. The ion energy was determined according to the ratios of activity of the analytical radionuclides, while the number of accelerated ions was calculated from the number of induced nuclei of the radionuclides. It was found that the velocities of the main group of protons and deuterons were the same within the measurement error, and the average number of ions accelerated in one pulse was, on average, 3 times higher when protons were accelerated.

In the framework of eiconal approximation and the double folding model, a formalism for calculating inclusive spectra of particles from stripping and fragmentation reactions involving light cluster nuclei is proposed. The cross-section of the 12C(3He, d)13N reaction at an incident particle energy of 81.4 MeV and the proton spectra from the deuteron fragmentation reaction with 56 MeV energies by 12C and 27Al nuclei are described. The calculated values satisfactorily fit the corresponding experimental data.

This work concerns the hydration mechanism of calcium zirconium aluminate as a ternary compound appearing in the CaO-Al2O3-ZrO2 diagram besides the calcium aluminates commonly used as the main constitutes of calcium aluminate cements (CACs). Moreover, a state-of-the-art approach towards significant changes in hydraulic properties was implemented for the first time in this work, where the effect of structural modification on the hydration behavior of calcium zirconium aluminate was proved by XRD, 27Al MAS NMR and SEM-EDS. The substitution of Sr2+ for Ca2+ in the Ca7ZrAl6O18 lattice decreases the reactivity of Sr-substituted Ca7ZrAl6O18 in the presence of water. Since the original cement grains remain unhydrated up to 3 h (Ca7ZrAl6O18) or 72 h (Sr1.25Ca5.75ZrAl6O18) of curing period in the hardened cement paste structures, strontium can be considered as an inhibition agent for cement hydration. The complete conversion from anhydrous 27AlIV to hydrated 27AlVI species was achieved during the first 24 h (Ca7ZrAl6O18) or 7 d(Sr1.25Ca5.75ZrAl6O18) of hydration. Simultaneously, the chemical shift in the range of octahedral aluminum from ca. 4 ppm to ca. 6 ppm was attributed to the transformation of the hexagonal calcium aluminate hydrates and Sr-rich (Sr,C)3AH6 hydrate into the cubic phase Ca-rich (Sr,C)3AH6 or pure C3AH6 in the hardened Sr-doped cement paste at the age of 7 d. The same 27Al NMR chemical shift was detected at the age of 24 h for the reference hardened undoped Ca7ZrAl6O18 cement paste.

L’IBA (Ion Beam Analysis) a été largement utilisée pour analyser quantitativement et avec une grande sensibilité la composition et les profils de profondeur des éléments dans les régions superficielles des solides. Pour l’analyse des éléments légers, on peut trouver des réactions nucléaires appropriées et, en particulier, les réactions induites par les deutérons, (d,p) ou (d,α), ont souvent des chaleurs de réaction Q élevées et des sections efficaces appréciables. Dans de nombreux cas de NRA (Nuclear Reaction Analysis) de films minces, des pics isolés de particules de réaction peuvent être obtenus avec un choix judicieux de l’angle de diffusion, de l’énergie du faisceau incident et des feuilles de filtrage devant le détecteur de particules chargées. Cependant, en général, la NRA génère des spectres complexes avec des pics qui se chevauchent, en particulier pour les échantillons épais. La connaissance des sections efficaces pour les cas de pics isolés est déjà utile pour concevoir des expériences visant à déterminer les contenus élémentaires des films minces. De nombreuses sections efficaces de ce type, par exemple 16O(d,p0)17O, 16O(d,p1)17O, 12C(d,p0), 14N(d,α0), ont été soigneusement mesurées dans des gammes d’énergie et d’angle d’intérêt analytique [87–90]. Il est parfois possible d’analyser plusieurs éléments légers simultanément par NRA. La connaissance des sections efficaces des réactions qui ne sont pas nécessairement d’un intérêt primordial pour l’analyse des couches minces, est alors souvent nécessaire pour les cas où les cibles contiennent des éléments donnant lieu à des réactions produisant des groupes de particules qui interfèrent avec le pic analytique primaire, et encore plus dans le cas de la NRA sur cible épaisse où l’élargissement des spectres de particules dû à l’épaisseur non nulle de la cible entraîne une probabilité beaucoup plus grande d’interférences élémentaires [26, 38, 91]. La nécessité de disposer de sections efficaces précises, même lorsqu’elles ne présentent pas un intérêt primordial pour un problème analytique spécifique, ou dans des gammes d’énergie qui ne sont pas directement utiles sur le plan analytique, s’est également accentuée récemment, avec l’introduction du concept d’IBA totale [92–94], dans lequel toutes les informations des spectres IBA [95] sont exploitées, et l’utilisation croissante de l’intelligence artificielle et des approches d’apprentissage automatique pour optimiser l’extraction d’informations de toutes les parties des spectres IBA. Jusqu’à présent, les réseaux neuronaux artificiels (ANN) ont été appliqués au cas de la spectrométrie de rétrodiffusion de Rutherford, où les sections efficaces sont connues analytiquement, mais l’extension fiable de ces techniques avancées de traitement des données à la NRA nécessite les meilleures sections efficaces de réaction nucléaire possibles. En outre, des sections efficaces de réaction nucléaire expérimentale précises sont nécessaires pour fournir des paramètres appropriées pour les approximations et les expressions appropriées des modèles théoriques de mécanismes de réaction nucléaire. L’oxygène étant l’élément le plus abondant de la croûte terrestre et en raison de l’importance universelle des oxydes dans les sciences de la terre et des matériaux, des sections efficaces précises pour les réactions nucléaires sur 16O et 18O ont déjà été déterminées [87, 96]. Le deuxième élément le plus abondant est le silicium, et bien qu’il s’agisse d’un élément de masse intermédiaire du point de vue de l’IBA, il y a également des réactions nucléaires d’intérêt analytique qui ont été déterminées [88, 97]. L’aluminium, troisième élément le plus abondant, est largement utilisé dans l’industrie pour ses propriétés mécaniques et électriques, ses applications décoratives et sa résistance aux agressions environnementales, notamment après une passivation électrochimique appropriée. L’aluminium est également largement présent dans les roches [...]
The overall objective of this thesis is to contribute experimentally determined and evaluated cross sections to a differential cross-section database for Ion Beam Analysis (IBA) that contains accurate and reliable data freely available to the user community, such as the Ion Beam Analysis Nuclear Data Library (IBANDL) database (https://www-nds. iaea.org/exfor/ibandl.htm) [1]. In the first part of the present thesis, we determined differential cross-sections of the reactions 27Al(d, p&α) and benchmarked them with thick target spectra derived from pure aluminum in two independent laboratories. The differential cross section of 27Al(d, p&α) reactions was determined between 1.4 MeV and 2 MeV at scattering angles of 165◦, 150◦, and 135◦ in the VDGT laboratory in Tehran (Iran), as well as measuring them again, including target preparation, at a scattering angle of 150° with independent equipment at INSP in Paris (France). We found close agreement between these two experimental measurements in two different laboratories at 150°. There is no nuclear reaction model that can be adjusted to represent these cross sections since the compound nucleus has a level structure that cannot be treated with current models. We proposed a fitted Fourier series function to represent the evaluated data to define the Al-cross sections. The evaluated differential cross sections have been benchmarked and validated using thick target charged particle spectra obtained using incident deuteron beams of energies between 1.6 MeV and 2 MeV at both laboratories. The validation was performed by fitting deuteroninduced particle spectra obtained from a high purity bulk Al target with SIMNRA, and the thick target spectra are reproduced, allowing the recommendation of the use of these cross sections for NRA. In the second part of the present thesis, the elastic proton scattering cross sections on 17O were measured for the first time at the SAFIR platform at INSP in Paris. Thin films of 17O were prepared by thermal oxidation of Si at 1100 ◦C under 17O2. The physical thickness of the silica was determined by ellipsometry and the atomic thickness by RBS with an uncertainty of 3%. The small quantities of 18O and 16O, present as impurities in the highly enriched 17O2 gas used to grow these films, were determined by the established NRA techniques using the 18O(p, α)15N and 16O(d, p1)17O nuclear reactions. We determined the yield of elastically scattered protons using the corresponding peak in the Elastic Backscattering (EBS) spectra; however, this peak sits on the large continuiiious signal from the silicon substrate. The Si signal was significantly suppressed by aligning the incident beam with the < 100 > axis of the single crystal silicon by ion channeling. The solid angle of the detector, placed at a scattering angle of 165◦, was determined by elastic scattering measurements of 2 MeV alpha particles on a reference sample of Bi implanted in Si. The measured 17O(p, p) cross section, with a systematic uncertainty of about 14%, consists of several resonant structures superimposed on a smoothly varying component increasing ranging from about 1.2 times the Rutherford cross section at 600 keV to about 3 times Rutherford at 2 MeV. A resonance at 1230 keV shows promise for EBS depth profiling, especially at large backscattering angles