14N Ions Research Articles

GITM‐Data Comparisons of the Depletion and Enhancement During the 2017 Solar Eclipse

AbstractThe total solar eclipse of 21 August 2017 was simulated with the Global Ionosphere‐Thermosphere Model (GITM), and the results were compared with the total electron content (TEC) measurements provided by the Global Navigation Satellite System, as well as F2 layer peak electron density (NmF2) derived from six ionosondes. TEC decreased over North America by ~54.3% in the model and ~57.6% in measurements, and NmF2 decreased by ~20–50% in the model and ~40–60% in the measurements. GITM predicted a posteclipse enhancement of ~10% in TEC and NmF2, consistent with observations which suggested an increase of ~10–25% in TEC and ~10–40% in NmF2. GITM showed that the divergence of horizontal winds drove the increase in Oxygen after the eclipse allowing an increase in the ionization rate. The slower charge exchange due to both the decreased ion temperature and N2 density allowed an increase of O+ density in the F region also.

Control of Ion Species and Energy in High-Flux Helicon-Wave-Excited Plasma Using Ar/N2 Gas Mixtures

The atomic nitrogen (N) ion flux and impacting ion energy are the two important parameters, which influence the performance of production of plasma nitridation applications such as N-doped graphene. In this paper, a novel method is described to control the flux and ion energy of atomic N ion (N+) and molecular N2 ion (N2+) using a helicon-wave-excited plasma (HWP) with Ar/N2 gas mixtures. It shows that by varying the flow-rate ratio of N2/(N2+Ar) ( $\alpha$ ), the ratio of [N+]/[N2+] ( $\beta$ ) can be controlled obviously, and $\beta $ could be increased up to 1.2 at $\alpha = 0.5$ , which is much higher than that in pure N2 HWP discharge ( $\beta \sim 0.2$ ). The maximum density and flux of atomic N+ are obtained, which are $2.5\times 10^{18}\,\,\text {m}^{-3}$ and $8.6\times 10^{21}\,\,\text {m}^{-2}\text {s}^{-1}$ , respectively. The results show that the addition of Ar into N2 plasma can be employed to remarkably increase the [N+]/[N2+] due to electron-impact ionization involving the metastable state of Ar. The N+ ion beams are formed with a speed near to Mach 3, and the ion-beam energy is increased from 30 to 50 eV with increasing $\alpha $ to 0.75.

Collision cross sections and transport coefficients of O−, O2−, O3− and O4− negative ions in O2, N2 and dry air for non-thermal plasmas modelling

The ions interaction data such as interaction potential parameters, elastic and inelastic collision cross sections and the transport coefficients (reduced mobility and diffusion coefficients) have been determined and analyzed in the case of the main negative oxygen ions (O−, O2−, O3− and O4−) present in low temperature plasma at atmospheric pressure when colliding O2, N2 and dry air. The ion transport has been determined from an optimized Monte Carlo simulation using calculated elastic and experimentally fitted inelastic collision cross sections. The elastic momentum transfer collision cross sections have been calculated from a semi-classical JWKB approximation based on a (n−4) rigid core interaction potential model. The cross sections sets involving elastic and inelastic processes were then validated using measured reduced mobility data and also diffusion coefficient whenever available in the literature. From the sets of elastic and inelastic collision cross sections thus obtained for the first time for O3−/O2, O2−/N2, O3−/N2, and O4−/N2 systems, the ion transport coefficients were calculated in pure gases and dry air over a wide range of the density reduced electric field E/N.

Visualization of complex DNA damage along accelerated ions tracks

The most deleterious DNA lesions induced by ionizing radiation are clustered DNA double-strand breaks (DSB). Clustered or complex DNA damage is a combination of a few simple lesions (single-strand breaks, base damage etc.) within one or two DNA helix turns. It is known that yield of complex DNA lesions increases with increasing linear energy transfer (LET) of radiation. For investigation of the induction and repair of complex DNA lesions, human fibroblasts were irradiated with high-LET 15N ions (LET = 183.3 keV/μm, E = 13MeV/n) and low-LET 60Co γ-rays (LET ≈ 0.3 keV/μm) radiation. DNA DSBs (γH2AX and 53BP1) and base damage (OGG1) markers were visualized by immunofluorecence staining and high-resolution microscopy. The obtained results showed slower repair kinetics of induced DSBs in cells irradiated with accelerated ions compared to 60Co γ-rays, indicating induction of more complex DNA damage. Confirming previous assumptions, detailed 3D analysis of γH2AX/53BP1 foci in 15N ions tracks revealed more complicated structure of the foci in contrast to γ-rays. It was shown that proteins 53BP1 and OGG1 involved in repair of DNA DSBs and modified bases, respectively, were colocalized in tracks of 15N ions and thus represented clustered DNA DSBs.

Fragments in heavy ion collisions in a hydrodynamic approach with a nonequilibrium equation of state

A hydrodynamic approach with a nonequilibrium equation of state is used to describe heavy ion collisions at medium energies. This approach includes describing the compression, dilution, and freeze-out stages of a hot spot formed during a heavy ion collision. The calculated energy spectra of protons and light 4He, 7Li, 9Be fragments produced in the 14N + 124Sn reaction at a 14N ion energy of 32 MeV/nucleon are compared to experimental data.

Hardening of reduced activation ferritic/martensitic steels under the irradiation of high-energy heavy-ion

In order to study the irradiation responses of reduced activation ferritic/martensitic (RAFM) steels which are candidates for fusion reactors, a reduced activation steel is irradiated at a terminal of HIRFL (heavy ion research facility in Lanzhou) with 63 MeV 14N ions and 336 MeV 56Fe ions at -50 ℃. The energies of the incident N/Fe ions are varied from 0.22 MeV/u to 6.17 MeV/u by using an energy degrader at the terminal, so that a plateau region of an atomic displacement damage (0.05-0.2 dpa) is obtained from the near surface to a depth of 24 μm in the specimens. Nanoindentation technique is used to investigate the nano-hardness changes of the samples before and after irradiation. The constant stiffness measurement is used to obtain the depth profile of hardness. The Nix-Gao model taking account of the indentation size effect (ISE) is used to fit the measured hardness and thus a hardness value excluding ISE is obtained. Consequently, the soft substrate effect for lower energy ion irradiation is effectively avoided. It is observed that there seems to be a power function relationship between the hardness and damage for the RAFM steel. The hardness initially increases significantly with the increase of irradiation damage, then increases slowly when the damage reaches to about 0.2 dpa. Positron annihilation is performed to investigate the defect evolution in the material. The positron annihilation lifetime spectra show that the long-lifetime proportion of the RAFM steel increases significantly after being irradiated. This means vacancy clusters are produced by the irradiation, resulting in the change of mechanics property. Even at low irradiation dose, point defects with high density are generated in the steel specimens, and subsequently aggregate into defect clusters, thereby suppressing the dislocation slip.The defect concentration in the material increases continuously with the increase of irradiation damage, which leads to the obvious irradiation hardening phenomenon. When the damage is higher than 0.1 dpa, the increment of mean lifetime gradually decreases due to the existence of a large number of vacancies and dislocations, and it eventually tends to be saturated, which explains why the irradiation hardening increment rate decreases with the increase of irradiation damage in the material.

Elastic and inelastic scattering of 15N ions by 7Li at 81 MeV versus that of 14N ions by 7Li at 80 and 110 MeV

Angular distributions of the elastic and inelastic scattering of 15N ions by 7Li nuclei were measured at the energy Elab(N15)=81 MeV(Ec.m.=25.77 MeV). The data were analyzed within the coupled-reaction-channels method. The elastic and inelastic scattering, spin reorientations of 7Li as well as the more important one- and two-step transfer reactions were included in the channels-coupling scheme. The parameters of Li7+N15 optical potential of Woods–Saxon form as well as deformation parameters of these nuclei were deduced. The analysis showed that the forward angle elastic scattering is dominated by pure potential scattering whereas the middle and large angle scattering gets a contribution from the ground state reorientation of 7Li. Contributions from particle transfers were negligible for the present scattering system. The Li7+N15 elastic scattering was compared with that of Li7+N14 at the energies Elab(N14)=80 MeV and 110 MeV. Different contributions to the elastic scatterings from other nuclear processes are shown to be responsible for the isotopic difference observed in the large angle scattering.

Stability and dissociation dynamics of N2 (++) ions following core ionization studied by an Auger-electron-photoion coincidence method.

An Auger-electron-photoion coincidence (AEPICO) method has been applied to study the stability and dissociation dynamics of dicationic states after the N K-shell photoionization of nitrogen molecules. From time-of-flight and kinetic energy analyses of the product ions, we have obtained coincident Auger spectra associated with metastable states of N2 (++) ions and dissociative states leading to N2 (++) → N(+) + N(+) and N(++) + N. To investigate the production of dissociative states, we present two-dimensional AEPICO maps which reveal the correlations between the binding energies of the Auger final states and the ion kinetic energy release. These correlations have been used to determine the dissociation limits of individual Auger final states.

The electronic spectrum of cryogenic ruthenium-tris-bipyridine dications in vacuo.

We report the electronic spectrum of the prototypical ruthenium coordination complex Ru(bpy)3 (2+) (bpy = 2, 2'-bipyridine) by messenger tagging with N2 in a cryogenic ion trap and photodissociation spectroscopy of mass selected Ru(bpy)3 (2+) ⋅ N2 ions. We observe individual electronic bands and groups of bands with unprecedented detail, particularly in the usually unresolved metal-to-ligand charge transfer region of the spectrum. By comparing our experimental results with time-dependent density functional theory, both with and without spin-orbit interaction [Heully et al., J. Chem. Phys. 131, 184308 (2009)], we are able to assign the spectrum of the isolated ion.

Time-resolved analysis and optical diagnostics of Trichel corona in atmospheric air

Trichel pulses of negative corona discharge in atmospheric air are investigated in a needle-to-plate configuration. Time-resolved images of the pulsed discharge are recorded by using an ICCD camera. Light emission spectra of N2 molecules and ions during the discharge are measured by optical diagnostics. The distributions of the positive ions and the reduced electric field along the discharge channel are analyzed accordingly. The results show that the positive ions that can accumulate in space and distort the electric field play an important role on the formation of the Trichel pulse. The Trichel pulse is a mode transition between low-current Townsend discharge and high-current glow discharge. The rising time of the pulse corresponds to the breakdown and formation of glow discharge, and the decay time is related to destroy the process of positive ion clouds and the quenching of glow discharge. The time interval between the pulses is determined by the re-accumulation of positive ions near the cathode in the low-current Townsend discharge to form the positive ion clouds as well as a strongly-distorted electric field.

Quantification of Hydrogen Concentrations in Surface and Interface Layers and Bulk Materials through Depth Profiling with Nuclear Reaction Analysis

Nuclear reaction analysis (NRA) via the resonant 1H(15N,αγ)12C reaction is a highly effective method of depth profiling that quantitatively and non-destructively reveals the hydrogen density distribution at surfaces, at interfaces, and in the volume of solid materials with high depth resolution. The technique applies a 15N ion beam of 6.385 MeV provided by an electrostatic accelerator and specifically detects the 1H isotope in depths up to about 2 μm from the target surface. Surface H coverages are measured with a sensitivity in the order of ~1013 cm-2 (~1% of a typical atomic monolayer density) and H volume concentrations with a detection limit of ~1018 cm-3 (~100 at. ppm). The near-surface depth resolution is 2-5 nm for surface-normal 15N ion incidence onto the target and can be enhanced to values below 1 nm for very flat targets by adopting a surface-grazing incidence geometry. The method is versatile and readily applied to any high vacuum compatible homogeneous material with a smooth surface (no pores). Electrically conductive targets usually tolerate the ion beam irradiation with negligible degradation. Hydrogen quantitation and correct depth analysis require knowledge of the elementary composition (besides hydrogen) and mass density of the target material. Especially in combination with ultra-high vacuum methods for in-situ target preparation and characterization, 1H(15N,αγ)12C NRA is ideally suited for hydrogen analysis at atomically controlled surfaces and nanostructured interfaces. We exemplarily demonstrate here the application of 15N NRA at the MALT Tandem accelerator facility of the University of Tokyo to (1) quantitatively measure the surface coverage and the bulk concentration of hydrogen in the near-surface region of a H2 exposed Pd(110) single crystal, and (2) to determine the depth location and layer density of hydrogen near the interfaces of thin SiO2 films on Si(100).

Quantification of Hydrogen Concentrations in Surface and Interface Layers and Bulk Materials through Depth Profiling with Nuclear Reaction Analysis.

Nuclear reaction analysis (NRA) via the resonant (1)H((15)N,αγ)(12)C reaction is a highly effective method of depth profiling that quantitatively and non-destructively reveals the hydrogen density distribution at surfaces, at interfaces, and in the volume of solid materials with high depth resolution. The technique applies a (15)N ion beam of 6.385 MeV provided by an electrostatic accelerator and specifically detects the (1)H isotope in depths up to about 2 μm from the target surface. Surface H coverages are measured with a sensitivity in the order of ~10(13) cm(-2) (~1% of a typical atomic monolayer density) and H volume concentrations with a detection limit of ~10(18) cm(-3) (~100 at. ppm). The near-surface depth resolution is 2-5 nm for surface-normal (15)N ion incidence onto the target and can be enhanced to values below 1 nm for very flat targets by adopting a surface-grazing incidence geometry. The method is versatile and readily applied to any high vacuum compatible homogeneous material with a smooth surface (no pores). Electrically conductive targets usually tolerate the ion beam irradiation with negligible degradation. Hydrogen quantitation and correct depth analysis require knowledge of the elementary composition (besides hydrogen) and mass density of the target material. Especially in combination with ultra-high vacuum methods for in-situ target preparation and characterization, (1)H((15)N,αγ)(12)C NRA is ideally suited for hydrogen analysis at atomically controlled surfaces and nanostructured interfaces. We exemplarily demonstrate here the application of (15)N NRA at the MALT Tandem accelerator facility of the University of Tokyo to (1) quantitatively measure the surface coverage and the bulk concentration of hydrogen in the near-surface region of a H2 exposed Pd(110) single crystal, and (2) to determine the depth location and layer density of hydrogen near the interfaces of thin SiO2 films on Si(100).

Nuclear point mass effects in the interaction of energetic ion with carbon nanotubes

We have calculated deposited energies of various energetic ions in carbon nanotubes, to study nuclear point mass effects, with the help of a static Monte Carlo (MC) simulation program. As a result of nuclear point mass effects, we show that at the same incident energy, the ion-deposited energy maximizes, while its mass has intermediate mass values, such as 11B, 12C and 14N ion masses, under hundreds keV 4He, 11B, 12C, 14N, 20Ne, 28Si and 40Ar ion irradiations of a thin-walled carbon nanotube. We also show that at the same incident energy, the coordination defect number maximizes, while its mass has an intermediate mass (20Ne) value, under hundreds keV 4He, 20Ne and 40Ar ion irradiations of the thin-walled nanotube. We derive an ion-deposited energy formula to analyze these maximum phenomena, and compare the MC simulation results with the MD (molecular dynamics) ones.

Probing the Dynamics of Rydberg and Valence States of Molecular Nitrogen with Attosecond Transient Absorption Spectroscopy.

An attosecond pulse is used to create a wavepacket in molecular nitrogen composed of multiple bound and autoionizing electronic states of Rydberg and valence character between 12 and 16.7 eV. A time-delayed, few-femtosecond, near-infrared (NIR) laser pulse is used to couple individual states in the wavepacket to multiple neighboring states, resulting in time-dependent modification of the absorption spectrum and revealing both individual quantum beats of the wavepacket and the energy shifts of the excited states in the presence of the strong NIR field. The broad bandwidth of the attosecond pulse and high energy resolution of the extreme ultraviolet spectrometer allow the simultaneous observation of time-dependent dynamics for many individual vibrational levels in each electronic state. Quantum beating with periods from 1.3 to 12 fs and transient line shape changes are observed among vibrational levels of a progression of electronically autoionizing Rydberg states leading to the excited A (2)Πu N2(+) ion core. Vibrational levels in the valence b (1)Πu state exhibit 50 fs oscillation periods, revealing superpositions between individual vibrational levels within this state. Comparisons are made to previous studies of electronic wavepackets in atoms that highlight similarities to atomic behavior yet illustrate unique contributions of the diatomic molecular structure to the wavepacket, including the influence of different electronic potentials and vibrational-level-specific electronic dynamics.

Elastic and inelastic scattering of 15N ions by 9Be at 84 MeV

Angular distributions of the 9Be + 15N elastic and inelastic scattering were measured at Elab(15N) = 84 MeV (Ec.m. = 31.5 MeV) for the 0–6.76 MeV states of 9Be and 0–6.32 MeV states of 15N. The data were analyzed within the optical model and coupled-reaction-channels method. The elastic and inelastic scattering, spin reorientations of 9Be in ground and excited states and 15N in excited states as well as the most important one- and two-step transfer reactions were included in the channels-coupling scheme. The parameters of the 9Be + 15N optical potential of Woods–Saxon form as well as deformation parameters of these nuclei were deduced. The analysis showed that the 9Be + 15N pure potential elastic scattering dominates at the forward angles whereas the ground state spin reorientation of 9Be gives a major contribution to the elastic scattering cross sections at the large angles. Contributions from particle transfers are found to be negligible for the present scattering system.

Quantification of nitrogen impurity and estimated Orowan strengthening through secondary ion mass spectroscopy in aluminum cryomilled for extended durations

The strength of aluminum alloys and composites processed through powder metallurgy can be improved through the addition of nano-scale dispersoids introduced during the cryomilling process. Quantification of Orowan strengthening from these dispersoids requires a reliable measurement of the impurity concentration. Secondary ion mass spectrometry (SIMS) was used to quantify the nitrogen impurity concentration using a 14N ion implanted standard. An analytical approach is devised to determine the nitrogen concentration of an aluminum alloy and composite based on SIMS measurements. Results are compared to the measurements carried out by gas fusion analysis. An increase in nitrogen concentration was observed with an increase in cryomilling time up to 72h. The nitrogen concentration varied from 1.64±0.17at% (0.80±0.08wt%) to 19.12±1.10at% (13.17±0.71wt%) for the 8h and 72h cryomilled nanocrystalline AA5083, respectively. Assuming that all nitrogen reacts to form dispersoids, the nitrogen concentration determined was used to calculate the volume and weight fractions of dispersoids, which in turn was used to estimate the strengthening contribution via Orowan strengthening. Orowan strengthening was calculated using dispersoids of 3, 9 and 15nm. The range of Orowan strengthening contribution was estimated, in MPa, to be from 7.69±0.78 to 3.03±0.31 for the 8h nanocrystalline AA5083 sample, and 154.97±10.29 to 61.09±4.06 for the 72h nanocrystalline AA5083 sample.

Laser-induced fluorescence from N2(+) ions generated by a corona discharge in ambient air.

In this work, we present the measurement of laser-induced fluorescence from N2(+) ions via the B(2)Σu(+)-X(2)Σg(+) band system in the near-ultraviolet. The ions were generated continuously by a plasma glow discharge in low pressure N2 and by a corona discharge in ambient air. The fluorescence decay time was found to rapidly decrease with increasing pressure leading to an extrapolated decay rate of ≍10(10) s(-1) at atmospheric pressure. In spite of this quenching, we were able to observe laser induced fluorescence in ambient air by means of a time-gated spectral measurement. In the process of comparing the emission signal with that of N2 spontaneous Raman scattering, ion concentrations in ambient air of order 10(8-)10(10) cm(-3) were determined. With moderate increases in laser power and collection efficiency, ion concentrations of less than 10(6) cm(-3) may be measurable, potentially enabling applications in atmospheric standoff detection of ionizing radiation from hazardous radioactive sources.

Energy loss effect on color center creation in LiF crystals under irradiation with 12C, 14N, 40Ar, 84Kr, and 130Xe ions

Color center creation in LiF crystals irradiated with 12C, 14N, 40Ar, 84Kr, and 130Xe MeV ions were studied as a function of the absorbed energy (fluence). For light ions (12C, 14N) the saturation of single F centers takes place at higher absorbed energy (5×1023eV/cm3) than that for 40Ar, 84Kr and 130Xe ions (∼1023eV/cm3). The saturation concentration of F centers for 12C and 14N (2×1019cm−3) is twice of that for the heavier ions. Further irradiation with light ions decreases concentration of F centers, presumably due to aggregation, whereas for heavy ions the saturation concentration remains approximately the same that can be explained by much stronger recombination losses within single tracks.

Elastic and inelastic scattering of 14N ions by 11B at 88 MeV versus that of 15N + 11B at 84 MeV

Full angular distributions for 11B + 14N elastic and inelastic scattering were measured at Elab(N14)=88 MeV (Ec.m.=38.7 MeV). The data were analyzed within the optical model and coupled-reaction-channels method which included the reorientations of 11B and 14N as well as the more important one- and two-step transfer reactions. The 11B + 14N optical potential parameters as well as deformation parameters of these nuclei were deduced. The 11B + 14N potential and data were compared with those of previously reported 11B + 15N data to explore isotopic differences in the scattering process. As has been shown in other cases of 11B scattering, the enhanced large-angle elastic and inelastic scattering data mostly arise from the ground-state reorientation of 11B.

Structural characteristics for phase transitions of [N(CH3)4]2CuCl4 by 13C CP/MAS NMR and 14N NMR

Structure geometry changes in [N(CH3)4]2CuCl4 near the phase transition temperature were studied by 13C CP/MAS NMR and 14N NMR spectrum. We distinguished the two chemically inequivalent N(1)(CH3)4 and N(2)(CH3)4 groups by 13C CP/MAS NMR and 14N NMR spectrum. The abrupt changes in chemical shifts and the split of the NMR signals near the phase transition temperatures for 13C and 14N are explained by a structural phase transition, implying that the structural geometry depends on the temperature. The mechanism behind this phase transition is based on ferroelasticity, and is also mainly related to the 14N ions in N(CH3)4 ions. Furthermore, both phases III and IV exhibit ferroelastic properties with identical orientational domains.