Pure ionization cross section of helium and ionization mechanism

Pure target ionization was investigated for 0.4-6.4 MeV C^q+(q = 1-4) + He and O^q+(q = 1-4) + He collisions. The double-to-single target ionization ratios R₂₁ were measured using coincidence techniques. We compare our results with existing experimental results and find they are in good agreement. The ratio R₂₁ is nearly independent of projectile charge state. The relation of R₂₁ ∼ V is analyzed using the over barrier model (OBM) and ionization probability, which is described in our extended over barrier model. Our calculation agrees well with the experimental results.     

Autoionization of N (q = 1-3) Rydberg states produced in high-energy collisions with He

Energy spectra of electrons ejected through autoionization decay of high-Rydberg states in high-energy collisions of N^q+ (q = 1-3) with He have been measured with high-resolution by using zero-degree electron spectroscopy. Several series of autoionizing lines were observed, corresponding to decays from N³⁺ 1s²2p(²P)nl Rydberg states produced in N³⁺ + He collisions, from N²⁺ 1s²2s2p(³P)nl Rydberg states produced in N²⁺ + He and from N⁺ 1s²2s2p²(⁴P)nl Rydberg states produced in N⁺ + He, respectively. Angular momentum distributions for the first or second peak of three series of Coster-Kronig electron transitions for N^q+ (q = 1-3) projectiles are also discussed, where the highly excited states are formed by electron excitation.     

Separation of potential and kinetic electron emission from Si and W induced by multiply charged neon and argon ions

The total secondary electron emission yields, γ_T, induced by impact of the fast ions Ne^q+ (q = 2-8) and Ar^q+ (q = 3-12) on Si and Ne^q+ (q = 2-8) on W targets have been measured. It was observed that for a given impact energy, γ_T increases with the charge of projectile ion. By plotting γ_T as a function of the total potential energy of the respective ion, true kinetic and potential electron yields have been obtained. Potential electron yield was proportional to the total potential energy of the projectile ion. However, decrease in potential electron yield with increasing kinetic energy of Ne^q+ impact on Si and W was observed. This decrease in potential electron yield with kinetic energy of the ion was more pronounced for the projectile ions having higher charge states. Moreover, kinetic electron yield to energy-loss ratio for various ion-target combinations was calculated and results were in good agreement with semi-empirical model for kinetic electron emission.     

Polarization effects on the cross-section of ion-atom collisions

Coupled-channel cross-sections for electron capture, ionization and electron loss due to polarization effects are calculated. The maximum impact parameter for electron escape is analyzed within the classical framework. The probabilities of ionization and capture are analyzed simultaneously by a semi-empirical method. Differing from the n-body classical trajectory Monte Carlo method, the condition for electron escape is determined by Coulomb forces related to the two nuclei. This method can be used to calculate coupled-channel cross-sections rather than single-channel ones in other methods. Therefore the calculated results can be compared with experimental data directly. In the low energy range, neglecting the ionization effect, the single-capture cross-sections of hydrogen atoms induced by various partially-stripped ions were calculated. In the high energy range, neglecting the capture effect on ionization, the pure-ionization cross-sections of neon atoms induced by Ne^q+ (q = 4, 6, 8) and Ar^q+ (q = 4, 6, 8, 10) at an incident energy E = 1.05 MeV/u were calculated. Good agreement was found between our calculation and experimental data in the literature. This method had been partially applied for intermediate energy successfully.     

Molybdenum L-shell X-ray production by 350-600 keV Xe (q = 25-30) ions

Molybdenum L-shell X-rays were produced by Xe^q+ (q = 25-30) bombardment at low energies from 2.65 to 4.55 keV/amu (350-600 keV). We observed a kinetic energy threshold of Mo L-shell ionization down to 2.65-3.03 keV/amu (350-400 keV). The charge state effect of the incident ions was not observed which shows that the ions were neutralized, reaching an equilibrium charge state and losing their initial charge state memory before production of L-shell vacancies resulted in X-ray production. The experimental ionization cross sections were compared with those from Binary Encounter Approximation theory. Taking into account projectile deflection in the target nuclear Coulomb field, the ionization cross section of Mo L-shell near the kinetic energy threshold was well described.     

Proton sputtering from polycrystalline Al surface interacting with highly charged ions at grazing incidence angle

Sputtering processes of protons from a polycrystalline Al surface interacting with Ar^q+ (q = 3-14) ions at a grazing incidence angle (∼0.5°) were investigated. The intensity of protons (I_H) detected in coincidence with scattered Ar atoms was measured as a function of q. I_H saturated at q ? 10, although it increased rapidly with q at 3 ? q ? 8. The angular distribution of protons with low kinetic energy (?2 eV) began to deviate from the cosine distribution and assumed a rather flat equidistribution as q increased. To analyze the sputtering processes of protons at the grazing incidence angle, a modified model of the “above-surface potential sputtering model” was proposed by considering image acceleration of projectile ions.     

Electron excitation cross sections of atomic hydrogen by fully stripped projectile ions

Electron excitation of atomic hydrogen by fully stripped projectile ions (q = 1-8) is theoretically studied by using the boundary corrected continuum intermediate state approximation in the energy range of 20-1000 keV/amu. In this formalism, we have taken a distortion effect produced by the projectile charge. The present computed results for the excited states (n = 2, 3, 4) of hydrogen atom with proton impact is only compared with experiments and other theoretical results. In addition, other results for different charge states (q = 1-8) are displayed in tabular form to get a detail view of contribution from different sub-shells. We have also studied the behavior of saturation of the cross sections which should tend to a constant value as the projectile charge increase.     

Calculation and analysis of n+Zr reactions in the En ⩽ 250 MeV energy range

All of reaction cross sections, angular distributions, energy spectra, γ-ray production cross sections, and the double differential cross section for neutron, proton, deuteron, triton, helium and alpha emission are calculated and analyzed for n+^{90,91,92,94,96,nat}Zr at incident neutron energies from 0.1 to 250 MeV. The optical model, intranuclear cascade model, the unified Hauser–Feshbach theory and the exciton model which included the improved Iwamoto–Harada model are used. Theoretical calculated results are compared with existing experimental data and other evaluated data from ENDF/B-VI.8, ENDF/B-VII.0 and JENDL-3.3. The optical model potential parameters are obtained according to the experimental data of total, nonelastic cross sections and elastic scattering angular distributions.     

Double differential cross sections of light charged particle emission in neutron induced reactions on Fe

The energy spectra and double differential cross sections of the light composite particle (deuteron, triton, helium and alpha-particle) emissions for n + ^54,56,57,58Fe reaction are studied by integrating the optical model, the intra-nuclear cascade model, direct reaction theories, equilibrium reaction theory and the exciton model which included the improved Iwamoto–Harada model. Theoretical calculated results are compared with existing experimental data.     

Double differential cross sections of n + Cu reactions

The energy spectra and double differential cross sections of neutron, proton, deuteron, triton, helium and alpha-particle emissions for n + ^63,65,nat.Cu reactions are calculated and analyzed at incident neutron energies below 200 MeV. The optical model, the intra-nuclear cascade model, direct reaction theories, the unified Hauser–Feshbach and exciton model which includes the improved Iwamoto–Harada model are used. Theoretically calculated results are compared with the existing experimental data.     

Influence of heat input waveform on transient critical heat flux of subcooled water flow boiling in a short vertical tube

The transient critical heat fluxes (CHFs) of the subcooled water flow boiling for ramp-wise heat input [Q = αt, α = 6.21 × 10⁸ to 1.63 × 10¹² W/m³ s, (q ≅ 1.08 × 10⁷ to 6.00 × 10⁷ W/m²)] and stepwise one [Q = Q_s, Q_s = 0 W/m³ at t = 0 s and Q_s = 2.95 × 10¹⁰ to 7.67 × 10¹⁰ W/m³ at t > 0 s, (q = 0 W/m² at t = 0 s and q ≅ 1.61 × 10⁷ to 3.87 × 10⁷ W/m² at t > 0 s)] with the flow velocities (u = 4.0-13.3 m/s), the inlet subcoolings (ΔT_sub,in = 86.8-153.3 K) and the inlet pressures (P_in = 742.2-1293.4 kPa) are systematically measured by an experimental water loop comprised of a pressurizer. The SUS304 tubes of inner diameters (d = 3, 6 and 9 mm), heated lengths (L = 33.15, 59.5 and 49.3 mm), L/d (=11.05, 9.92 and 5.48), and wall thickness (δ = 0.5, 0.5 and 0.3 mm) respectively with the rough finished inner surface (surface roughness, Ra = 3.18 μm) are used in this work. The experimental errors in the subcooling measure and the pressure one are ±1 K and ±1 kPa, while in the heat flux it is ±2%. The transient CHF data for the ramp-wise heat input and the stepwise one are compared with those for the exponentially increasing heat input (Q = Q₀ exp(t/τ), τ = 16.82 ms to 15.52 s) previously obtained and the dominant variables on transient CHF for heat input waveform difference are confirmed. The transient CHF data are compared with the values calculated by the steady state CHF correlations against inlet and outlet subcoolings, and the applicability of steady state CHF correlations is confirmed extending its possible validity for the reduced time, ω_p, down to 800 ms. The transient CHF data are compared with the values calculated by the transient CHF correlations against inlet and outlet subcoolings, and the influence of heat input waveform on transient CHF is clarified based on the experimental data for the ramp-wise heat input, the stepwise one and the exponentially increasing one. The dominant mechanisms of the subcooled flow boiling critical heat flux for the ramp-wise heat input, the stepwise one and the exponentially increasing one are discussed.     

Thermal conductivities of hypostoichiometric (U, Pu, Am)O2−x oxide

The thermal conductivities of (U_0.68Pu_0.30Am_0.02)O_2.00−x solid solutions (x = 0.00-0.08) were studied at temperatures from 900 to 1773 K. The thermal conductivities were obtained from the thermal diffusivities measured by the laser flash method. The thermal conductivities obtained experimentally up to about 1400 K could be expressed by a classical phonon transport model, λ = (A + BT)⁻¹, A(x) = 3.31 × x + 9.92 × 10⁻³ (mK/W) and B(x) = (−6.68 × x + 2.46) × 10⁻⁴ (m/W). The experimental A values showed a good agreement with theoretical predictions, but the experimental B values showed not so good agreement with the theoretical ones in the low O/M ratio region. From the comparison of A and B values obtained in this study with the ones of (U,Pu)O_2−x obtained by Duriez et al. [C. Duriez, J.P. Alessandri, T. Gervais, Y. Philipponneau, J. Nucl. Mater. 277 (2000) 143], the addition of Am into (U, Pu)O_2−x gave no significant effect on the O/M dependency of A and B values.     

Electron emission by highly charged neon and xenon ions on fusion-relevant tungsten and graphite surfaces

Here we report highly charged ⁴⁰Ne^q+ (q = 3-8) and ¹²⁹Xe^q+ (q = 10-30) ion-induced secondary electron emission on the tungsten and highly oriented pyrolytic graphite (HOPG) surfaces. The total secondary electron yield is measured as a function of the potential energy of incident ion. The experimental data is used to separate contributions of kinetic and potential electron yields. We estimate roughly 10% of ion’s potential energy is consumed in potential electron emission. The rest of the ion’s potential energy is responsible for the sputtering and material modification.     

Atomic data and spectral line intensities for S XIII

Electron impact collision strengths, energy levels, oscillator strengths, and spontaneous radiative decay rates are calculated for S XIII. The configurations used are 2s², 2s2p, 2p², 2l3l′, 2l4l′ and 2s5l′, with l = s, p and l′ = s, p, d, giving rise to 92 fine-structure levels in intermediate coupling. Collision strengths are calculated at seven incident energies (10, 20, 45, 90, 135, 180, and 225 Ry) for the transitions within the three lowest configurations, and five incident energies (45, 90, 135, 180, and 225 Ry) for transitions between the lowest five levels and the n = 3, 4, 5 configurations. Calculations have been carried out using the distorted wave approximation. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates of the present work, and R-matrix results for the 2s², 2s2p, 2p² configurations available in the literature, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10⁸-10¹⁴ cm⁻³ at an electron temperature of log T_e(K) = 6.4, corresponding to the maximum abundance of S XIII. Spectral line intensities are calculated, and their diagnostic relevance is discussed. Observed line ratios indicate electron temperatures of the emitting plasma close to log T_e(K) = 6.4. This dataset will be made available in the next version of the CHIANTI database.     

Calculation and analysis of p + Ca reaction cross sections at incident energies from threshold to 250 MeV

All cross sections, angular distributions and energy spectra of neutron, proton, deuteron, triton, helium, alpha particle emission for p + ^{40,42,43,44,46,48,nat}Ca reactions have been calculated and analyzed at incident proton energies from threshold to 250 MeV by nuclear theoretical models. The theoretical calculated results are in good agreement with existing experimental data.     

Atomic data and spectral line intensities for Mg VI

Electron impact collision strengths, energy levels, oscillator strengths, and spontaneous radiative decay rates are calculated for Mg VI. The configurations used are 2s²2p³, 2s2p⁴, 2p⁵, 2s²2p²3s, 2s²2p²3p, and 2s²2p²3d, giving rise to 72 fine-structure levels in intermediate coupling. Collision strengths are calculated at five incident energies, 12, 24, 36, 48, and 60 Ry. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10⁸-10¹⁴ cm⁻³ at an electron temperature of log T_e (K) = 5.6, corresponding to maximum abundance of Mg VI. Relative and absolute spectral line intensities are calculated and compared with observations of a solar active region.     

Effects of dissolved oxygen on electrochemical and semiconductor properties of 316L stainless steel

The effects of dissolved oxygen on the electrochemical behavior and semiconductor properties of passive film formed on 316L SS in three solutions with different dissolved oxygen were studied by using polarization curve, Mott-Schottky analysis and the point defect model (PDM). The results show that higher dissolved oxygen accelerates both anodic and cathodic process. Based on Mott-Schottky analysis and PDM, the key parameters for passive film, donor density N_d, flat-band potential E_fb and diffusivity of defects D₀ were calculated. The results display that N_d(1−7 × 10²⁷ m⁻³) and D₀(1−18 × 10⁻¹⁶ cm²/s) increase and E_fb value reduces with the dissolved oxygen in solution.     

Simultaneous ionization and excitation of helium by electron impact

We present numerical results for He (1s²) (e, 2e) He⁺ reaction process for transitions to the n = 1, 2 and 3 states of He⁺ for noncoplanar symmetric geometry at incident energies of 1000 and 1600 eV. The calculations are performed using the plane wave impulse approximation (PWIA) and the 3C method (also called the Brauner, Briggs and Klar (BBK) model) that includes post collision interaction and multiple scattering effects. In both the methods we have used the highly correlated configuration interaction wave function for the ground state of helium. A comparison of the present theoretical cross sections with the recent measured data of Ren et al. [X.G. Ren, C.G. Ning, J.K. Deng, G.L. Su, S.F. Zhang, Y.R. Huang, G.Q. Li, Phys. Rev. A 72 (2005) 042718] shows reasonably good agreement.