Comparison of secondary ion emission yields for poly-tyrosine between cluster and heavy ion impacts

Emission yields of secondary ions necessary for the identification of poly-tyrosine were compared for incident ion impacts of energetic cluster ions (0.8 MeV , 2.4 MeV , and 4.0 MeV ) and swift heavy monoatomic molybdenum ions (4.0 MeV Mo⁺ and 14 MeV Mo⁴⁺) with similar mass to that of the cluster by time-of-flight secondary ion mass analysis combined with secondary ion electric current measurements. The comparison revealed that (1) secondary ion emission yields per impact increase with increasing incident energy within the energy range examined, (2) the 4.0 MeV impact provides higher emission yields than the impact of the monoatomic Mo ion with the same incident energy (4.0 MeV Mo⁺), and (3) the 2.4 MeV impact exhibits comparable emission yields to that for the Mo ion impact with higher incident energy (14 MeV Mo⁴⁺). Energetic cluster ion impacts effectively produce the characteristic secondary ions for poly-tyrosine, which is advantageous for highly sensitive amino acid detection in proteins using time-of-flight secondary ion mass analysis.     

Crystallographic measurement of the β to α phase transformation and δ-hydride precipitation in a laser-welded Zircaloy-2 tube by electron backscattering diffraction

Crystallographic measurement of the β to α phase transformation and δ-hydride precipitation in a laser-welded Zircaloy-2 ferrule tube were carried out using an electron backscattering diffraction pattern (EBSP). A basket-weave structure with sub-micron lath width caused by quenching from the β to α phase was observed in the heat-affected and fusion zones, and mainly showed a grain boundary misorientation angle of 60° with an <1 1  0> rotation axis. This result is consistent with the Burgers orientation relationship of {1 1 0}_β//(0 0 0 1)_α and <1 1 1>_β//<1 1  0>_α for the β to α phase transformation. The texture of the quenched α′ phase was strongly inherited from the original α phase, having a radial (0 0 0 1) basal pole and axial {1 1  0} textures, even in the fusion zone. The primary hydride habit plane in the welded Zircaloy-2 was (0 0 0 1)_α//{1 1 1}_δ, matching previously obtained results for recrystallized cladding tubes. In addition to the primary habit plane, secondary habit planes were observed for the other low-index planes {1 0  0} and {1 0  1} in the fusion zone. The heterogeneous accumulation of hydrides in the transition zone between heat-affected and unaffected zones was mainly due to the residual stress distribution in the narrow region.     

The interaction of antihydrogen with simple atoms and molecules

In this paper, we describe calculations that we have carried out of cross sections for rearrangement processes in very low-energy helium + antihydrogen scattering that result in or or . A significantly more accurate method from that used previously [E.A.G. Armour, S. Jonsell, Y. Liu, A.C. Todd, Nucl. Instr. and Meth. B 247 (2006) 127] is used to calculate the entrance channel wave function. Results are presented for the first two processes. Mention is made of the use of the method in calculations of low-energy e⁺H₂ scattering.     

Estimation of equilibrium surface precipitation constants for trivalent metal sorption onto hydrous ferric oxide and calcite

Equilibrium constants for modeling surface precipitation of trivalent metal cations (M³⁺) onto hydrous ferric oxide and calcite were estimated from linear correlations of standard state Gibbs free energies of formation, () of the surface precipitates. The surface precipitation reactions were derived from Farley et. al. [K.J. Farley, D.A. Dzombak, F.M.M. Morel, J. Colloid Interface Sci. 106 (1985) 226] surface precipitation model, which are based on surface complexation model coupled with solid solution representation for surface precipitation on the solid surface. The values were correlated through the following linear free energy relations and where ‘ss’ stands for the end-member solid component of surface precipitate, is in kJ/mol, r_M³⁺ is the Shannon-Prewitt radius of M³⁺ in a given coordination state (nm), and is the non-solvation contribution to the Gibbs free energy of formation of the aqueous M³⁺ ion. Results indicate that the above surface precipitation correlations are useful tools where experimental data are not available.     

Anisotropy of disorder accumulation and recovery in 6H-SiC irradiated with Au ions at 140 K

Single crystal 〈0 0 0 1〉-oriented 6H-SiC was irradiated with Au²⁺ ions to fluences of 0.032, 0.058 and 0.105 ions/nm² at 140 K and was subsequently annealed at various temperatures up to 500 K. The relative disorder on both the Si and C sublattices has been determined simultaneously using in situ D⁺ ion channeling along the 〈0 0 0 1〉 and 〈〉 axes. A higher level of disorder on both the Si and C sublattices is observed along the 〈〉. There is a preferential C disordering and more C interstitials are aligned with 〈0 0 0 1〉. Room-temperature recovery along 〈〉 occurs, which is associated with the 〈0 0 0 1〉-aligned interstitials that annihilate due to close-pair recombination. Disorder recovery between 400 and 500 K is primarily attributed to annihilation of interstitials that are misaligned with 〈0 0 0 1〉 and to epitaxial crystallization. Effects of stacking order in SiC on disorder accumulation are insignificant; however, noticeable differences of low-temperature recovery in Au²⁺-irradiated 6H-SiC and 4H-SiC are observed.     

Development of secondary ion mass spectroscopy using medium energy C60 ion impact

In this paper, we report time-of-flight (TOF) secondary ion mass spectroscopy using primary C₆₀ ions with an energy range from several tens of keV to several hundreds of keV. Application of the spectroscopy to the analysis of a poly(amino acid) film revealed that characteristic peaks, necessary for identification of the amino acid in proteins, show higher intensities for medium energy C₆₀ (120 keV and 540 keV ) impacts than those for low energy C₆₀ (30 keV ) impacts. This finding demonstrates that medium energy C₆₀ ion impacts are useful for highly sensitive characterization of amino acids.     

Radiation-induced decomposition of anion exchange resins

Radiation-induced degradation of the strongly basic anion exchange resin Amberlite™ IRA400 in , Cl⁻ and OH⁻ forms has been studied. The research focused on the formation of molecular hydrogen in the gamma-radiolysis of water slurries of these quaternary ammonium resins with varying water content. Extended studies with various electron scavengers (, N₂O and O₂) prove an important role of in the formation of H₂ from these resins. An excess production of H₂ in these systems at about 85% water weight fraction was found to be due to trimethylamine, dimethylamine and other compounds that leach from the resin to the aqueous phase. Irradiations with 5 MeV ⁴He ions were performed to simulate the effects of α-particles.     

Study of the electronic structures of oxygen doped in LiBaF3 crystal

The most likely substituting positions of impurity oxygen ions in LiBaF₃ crystals are studied using the general utility lattice program (GULP). The calculated results indicate that the main defect model is [] in the O:LiBaF₃ crystal. The electronic structures of the LiBaF₃ crystal with the defect [] are calculated using the DV-Xα method. It can be concluded from the electronic structures that the LiBaF₃ crystal with the defect [] will exhibit a 217-280 nm absorption band and the impurity oxygen will decrease core-valence luminescence yield.     

First principle studies on the electronic structures and absorption spectra in KMgF3 crystal with fluorine vacancy

The experiments indicate that the perfect KMgF₃ crystal has no absorption in the visible range, however the electron irradiation induces a complex absorption spectrum. The absorption spectra can be decomposed by five Gaussian bands peaking at 2.5 eV (488 nm), 3.4 eV (359 nm), 4.2 eV (295 nm), 4.6 eV (270 nm) and 5.2 eV (239 nm), respectively. The purpose of this paper is to seek the origins of the absorption bands. The electronic structures and absorption spectra either for the perfect KMgF₃ or for KMgF₃: with electrical neutrality have been studied by using density functional theory code CASTEP with the lattice structure optimized. The calculation results predicate that KMgF₃: also exhibits five absorption bands caused by the existence of the fluorine ion vacancy and the five absorption bands well coincide with the experimental results. It is believable that the five absorption bands are related to in KMgF₃ crystal produced by the electron irradiation.     

Effects of the radiative recombination on the intensity and polarization of the Ly-α emission of hydrogen-like ions

The intensity ratio of the to photon emission is analyzed for hydrogen-like Fe²⁵⁺ ions if their excitation arises in a plasma not only from the electron impact but also due to the radiative recombination (RR) of initially bare Fe²⁶⁺ ions. Under such conditions, the intensity ratio and the (degree of) linear polarization of the Ly-α₁ line are explored for collisions with an electron beam over a wide range of kinetic energies up to 50 keV. Apart from the direct population of the 2p_1/2,3/2 levels via the RR of bare ions, the contributions from radiative cascades and higher multipoles are taken into account by applying a fully relativistic theory for the motion of the electrons and the electron-photon coupling. Our calculations show an overall small effect of the RR upon the degree of the Ly-α₁ polarization as well as the intensity ratio under usual plasma conditions. However, the effects from the RR of initially bare ions may become significant at electron beam energies , for plasma conditions far away from ionization equilibrium with a relatively large proportion of bare Fe ions, as it may be realized in electron-beam ion trap experiments.     

Atomistic simulations of nanometric dislocation loops in bcc tungsten

Small dislocation loops formed from self-interstitial atoms (SIAs) are commonly found in irradiated metals. These defects significantly influence the mechanical properties of the materials. Atomistic simulations are used to describe nanometric circular dislocation loops with Burger’s vectors , and in bcc tungsten. Particular attention is paid to the habit plane of the loop. Two different embedded atom model (EAM) potentials are used. The energetics and geometry of the loops are studied as a function of their size.     

Temperature dependence of damage formation in Ag ion irradiated 4H-SiC

Rutherford backscattering spectrometry (RBS) in channelling mode was used to study the defect formation in silver (Ag) ion irradiated silicon carbide (SiC). The 4H-SiC samples were irradiated with 360 keV Ag ions at different temperatures (15, 295, 375, 475, 625 and 875 K) over a wide range of fluences (1×10¹¹ to , depending on the irradiation temperature). The results can be divided into two groups: (i) for irradiation temperatures between 15 and 475 K amorphisation of the implanted layers is reached for ion fluences between 7×10¹³ and . The over-all cross-section of defect production at very low ion fluences which comprises the formation of point defects and of amorphous clusters, is almost identical for all data sets measured in this temperature range. Differences in the damage evolution which occur at higher ion fluences, suggest that the relative contribution of amorphous clusters within single ion impacts in crystalline material decreases with rising temperature. (ii) For irradiations performed at 625 and 875 K no amorphisation is found for ion fluences as high as . With increasing ion fluence the defect concentration exhibits a distinctive plateau due to the balance between formation and recombination of point defects before increasing up to a saturation level well below amorphisation. For this final stage our results indicate a mixture of point defect clusters and extended defects most probably dislocations. A comparison with data from the literature suggests that the damage evolution for implantation at 625 and 875 K is strongly influenced by the mobility of vacancies starting at around 600 K.     

Morphology and interface structure of α-Fe2O3 islands grown on sapphire by ion-implantation and annealing

The morphology and interface structure of α-Fe₂O₃ islands grown on α-Al₂O₃ single crystals (sapphire) by Fe-ion-implantation and annealing in an oxidizing atmosphere have been studied using transmission electron microscopy. The α-Fe₂O₃ islands have the orientation relationship of and with sapphire. The typical outline of α-Fe₂O₃ islands consists of two (0 0 0 1) and six planes. The interfaces between α-Fe₂O₃ islands and sapphire are semicoherent, that is coherent regions separated by misfit dislocations at the interfaces. When imaged along the direction, the projected Burgers vector is determined to be . When imaged along the direction, the projected Burgers vector is determined to be . These misfit dislocations form a network structure at the interface to accommodate the mismatch between the lattices of the α-Fe₂O₃ and the α-Al₂O₃.     

First-principles study on electronic structures and absorption spectra for BaWO4 crystal containing barium vacancy

The electronic structures, dielectric function and absorption spectra for the perfect BaWO₄ (BWO) crystal and the BWO crystal containing barium vacancy () have been studied using density functional theory code CASTEP with the lattice structure optimized. The results indicate that the optical properties of the BWO crystal exhibit anisotropy and its optical symmetry coincide with lattice structure geometry of the BWO crystal. For the BWO crystal containing , there exhibit four absorption bands peaking at 0.71 eV (1751 nm), 1.85 eV (672 nm), 3.43 eV (362 nm) and 3.85 eV (322 nm), respectively. The origins of the 370 nm absorption band should be related to the .     

Tracer diffusion of Mn in alloy D9 in presence of sodium

The diffusivity of manganese in vacuum annealed and cold worked alloy D9 in presence of sodium was measured by the standard tracer technique. The lattice diffusion coefficient of manganese in vacuum annealed alloy D9 specimens in the temperature range 773-873 K is given by the expression and that in cold worked alloy D9 specimens is given by where R is in J K⁻¹ mol⁻¹. The activation energy for diffusion in cold worked specimens is less than that in vacuum annealed specimens. The activation energy for diffusion of manganese in presence of sodium is almost four times less than that in various austenitic stainless steels reported in the literature.     

Preparation of Ne, Mg, Si, S, and Ar targets by ion implantation into thin carbon foils

The preparation of isotopically pure targets of ²⁰Ne, ²⁴Mg, ²⁸Si, ³²S, and ³⁶Ar by the implantation of 25-70 keV ions into carbon foils is described.