Search

keV-energy Na+ ions are scattered from clean and water covered Cu(1 1 0) surfaces in grazing incidence. For both surfaces the pronounced Na° fractions decrease with incident energy. In particular, the lower Na° fraction has been observed for the water covered Cu(1 1 0) surface. The simple calculations using rate equation are presented to compare with the experimental data. The calculation is in agreement with the experimental data. It indicates that the water covered Cu(1 1 0) surface has the slightly higher work function due to water molecules dissociation and forming hydroxyl groups, so that the neutral fraction on water covered Cu(1 1 0) is lower than that on the clean surface.

Aluminum hydride (AlH3), an attractive hydrogen storage material, plays an important role in rocket and aerospace industry. The impurities in aluminum hydride may seriously cause the deterioration in its properties and stability. Mixing AlH3 sample with the known content of silicon, we distinguish the elements in AlH3 and determine their concentration by using PIXE, XPS and elemental analyzer. Al, Si, Cl, Ca and Fe were identified by PIXE. XPS technique was used to measure the oxidized product of the mixed silicon. C, H content were obtain from the elemental analyzer. The results of the impurity concentration show the effectiveness of the synergy among these techniques except carbon. The XPS result from the pristine sample shows the concentration of carbon is 6 times larger than the major element Al while the result from the elemental analyzer is only 0.620 wt%. It suggests that the XPS technique is surface-sensitive and not well suited to the determination of the bulk concentration of carbon. The mass fraction ratio of Al to H is μ Al / H = 8.718 27 3 , which indicates that the product partly decomposes.

Jellium model is well known and used to understand the neutralization of alkali-metal ions on metal surfacesbut we find it cannot explain our experiments for the neutralization of 0.4 keV and 0.8 keV Na+ ions on Al(1 1 1) and Cu(1 1 0) surfaces in grazing incidence. As the exit angle increases neutral fractions on Cu(1 1 0) surface decreases first and then increases which is similar to our previous results at large scattering angles. While for the Al(1 1 1) surface we observe opposite characteristics. This anomalous bell-shaped feature cannot be explained by the Jellium model. One possible explanation is the inner 2p electron promotion at smaller exit angles this may cause the Na* excited states to be generated and produce excess Na+ ions while the similar electronic excitation process is inefficient for the Cu(1 1 0) surface in the present energy range.

It is well known that vacancy (Vac) can trap multiple hydrogen (H) atoms, and many Vac-rhenium (Re) and Vac-osmium (Os) clusters can be formed in tungsten (W) under fusion neutron irradiation, but the behaviors of H in Vac-Re/Os clusters are still unclear. Therefore, in this work, first-principles calculations are used to investigate the effects of transmutation elements of Re and Os on the H trapping ability of vacancy in W. We find that the presence of multiple Re/Os atoms around vacancy can significantly decrease the trapping energy of vacancy on H and the number of H atoms trapped in vacancy in W, thus Re/Os has an inhibiting effect on the growth of H bubble. Furthermore, Os has more prominent influence than Re for H trapping ability of vacancy in W. In addition, compared with VacHm in pure W, the presence of 8 Re atoms around vacancy in W would increase the stability of VacHm for m ≤ 4, but reduce the stability of VacHm for m > 4. Based on those results, we can qualitatively explain the recent experimental phenomenon.

Charge transfer during oxygen negative ion surface scattering is performed to investigate the electronic interaction for the water/Cu system as a function of incident velocity. We find that both positive and negative ion fractions increase with incident velocity for the specular scattering condition. The positive ions produced close to the surface can be understood by the mechanisms of collision-induced ionization and Auger ionization, and they finally survive from the resonant and/or Auger neutralization, which are well described by the exponential scaling. The negative ions are formed through the resonant charge transfer, and the velocity dependence has been explained by the kinematically parallel velocity effect and the surface work function. The modified rate equation taking into account these two factors is in rough agreement with the experimental result.

Li+ and Na+ ions are scattered from Au(1 1 0) and Au(1 1 1) surfaces in the keV-energy range, respectively. The pronounced Li° and Na° fractions non-monotonically vary with incident energy and exit angle for high work function gold surfaces. In particular, the azimuthal angle dependence of Li° fraction has been observed at low incident energies for a grazing exit angle. The simple calculations are presented to compare with the experimental data. Our findings clearly indicate that both the perpendicular and parallel exit velocity affect the final neutral fraction.

L-shell X-rays of 48Cd and 49In have been measured for the bombardment of protons in the energy range 75–250 keV in steps of 25 keV. The individual Lι, Lα, Lβ, Lγ and total L X-ray production cross sections were extracted from the yield. The results were compared with theoretical predictions of PWBA, ECPSSR and ECUSAR, as well as with experimental results of other authors. Good agreements were observed for our data with others and ECPSSR or ECUSAR calculations. The influence of using different atomic parameter databases is also discussed.

L x rays of Nd have been measured for the bombardment of protons with the energies of 100–250 keV. It is found that Lγ 2 (abbreviation of Lγ 2,3,4,4 ′) x-ray emission is largely enhanced by proton impact, compared to the case of photon radiation. It is proposed that is caused by the multiple-ionization of outer-shell electrons. To verify this explanation, the enhancement for relative intensity ratio of Lι and Lβ 2 to Lα x ray and the energy shift of various L-subshell x rays are discussed. In addition, the production cross sections of Lι, Lα, Lβ and Lγ x ray are obtained and compared with theoretical calculations of PWBA, ECPSSR and ECUSAR, along with various atomic parameter databases.

In this work, we present negative-ion fractions as a function of exit velocity and angle after keV-energy negative oxygen and carbon ions scattering on a highly oriented pyrolytic graphite (HOPG) surface, at a scattering angle of 38°. The negative-ion fractions increase monotonously with the increase of exit velocity for specular scattering, while negative-ion fractions present a bell-shaped dependence on exit angle. In order to gain further insight into the nature of charge transfer on HOPG, a modified charge transfer model involving the contribution of positive ions has been proposed and roughly reproduced the velocity and angle dependences of negative-ion fractions.

We have measured the electron and X-ray emission of tungsten bombarded with proton in the energy range of 50–250 keV. It is found that the total electron yield mainly consists of kinetic electron emission, which results from the excited valence electrons, and presents a similar trend to the curve of stopping power. The ratio between electron yield and electronic energy loss is not constant, but decreases with increasing incident energy. The behavior is interpreted by an expected competitive mechanism of ionization between different shell electrons of target atom. The explanation is verified by the experimental increase of M-shell X-ray emission yield, and the measured and calculated ionization cross section of core and valence electrons.

Muscovite mica sheets were bombarded by lithium, carbon and oxygen ions in the energy range from several hundred keV to several MeV. The induced surface structures were measured in the air with atomic force microscopy (AFM) in the tapping mode. The hillock-like structure on the mica surface was observed. The height of the hillock increases linearly when the energy loss is above 1.2 keV/nm. The induced structures are similar with the similar electronic stopping powers but different projectiles for muscovite mica.

The interaction of 16 keV Cu − ions with Al 2 O 3 nano-capillaries of 50 nm diameter and 10 μm length was studied. The angular and charge state distributions of the transmitted particles were measured by a position-sensitive microchannel plate detector. It shows that transmitted particles appear as two peaks and consist of three charge states, Cu − , Cu 0 and Cu + . As the tilt angle increases, more Cu − ions lose electrons resulting in the formation of Cu 0 and Cu + during multiple collisions with the capillary walls. Unlike previously reported results on highly charged ions, keV-energy Cu − ions undergo significant charge exchange processes with the inner walls of the capillaries. This indicates that the guiding effect is absent in the negative ion transmission under the very low ion current conditions.

In this paper, the projectile electron loss cross sections of He+, Li+, Li2+ and C2+ colliding with atomic hydrogen are studied in the frame work of the extended over-barrier model at intermediate velocities (25–600 keV/u). The electron loss cross sections are calculated in terms of the interaction between the screened target nucleus and the active projectile electron and of the interaction between the projectile electron and the target electron. Compared with the measurements, this model satisfactorily reproduces the experimentally obtained energy dependence of the single electron loss cross sections over the energy range investigated here.

Molybdenum L-shell X-rays were produced by Xeq+ (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. (C) 2010 Published by Elsevier B.V.

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.

Since the successful completion of the cooling storage ring (CSR) project in China at the end of 2007, high qualitative heavy ion beams with energy ranging from keV to GeV/u have been available at the Heavy Ion Research Facility at Lanzhou (HIRFL). More than 10 9 1 GeV/u C 6+ particles or 10 8 235 MeV/u Xe particles can be stored in the CSR main-ring and extracted within hundred nano-seconds during the test running, the beam parameters will be improved in the coming years so that high energy density (HED) conditions could be achieved and investigated there. Recent scientific results from the experiments relevant to plasma research on HIRFL are summarized. Dense plasma research with intense heavy ion beams of CSR is proposed here.

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 R 21 were measured using coincidence techniques. We compare our results with existing experimental results and find they are in good agreement. The ratio R 21 is nearly independent of projectile charge state. The relation of R 21 ∼ 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.

In this paper, an extension of the already-developed and modified over-barrier model is presented to study theoretically one and two electron transitions between helium atoms and multiply charged ion collisions at a low-to-intermediate velocity (v(Bohr) similar to 5v(Bohr)). It is found that the present model can partially reproduce the experimentally obtained velocity dependence of the absolute cross-sections which is also supported by the results of the classical trajectory Monte Carlo (CTMC) method. (c) 2007 Elsevier B.V. All rights reserved.

We measured the double-to-single ionization ratios R of Helium bombarded by Cq+ and Oq+ ions (q = 1 ∼ 3). The velocity of the projectile varies from vBohr to 4 vBohr, the energy varies from 25 keV/amu to 500 keV/amu. The value of R increases rapidly with the collision velocity and reaches the maximum when the velocity is about 2 or 3 vBohr, then it decreases slowly for the higher velocity. A simple model is presented to estimate the value R varying with the collision velocity. The results calculated by the model are in agreement with the experimental data basically.

The X-ray emission induced by highly charged argon and xenon ions impinging on a beryllium surface is investigated. It is found that spectra of the X-ray induced by Ar 17,18+ interacting with the surface are very different from those of the X-ray induced by Ar 17,18+ interacting with residual gases. The result provides an experimental evidence for the existence of hollow atoms below the surface. Several unexpected X-ray lines are also found in the experiment. Firstly, K X-rays are observed when Ar 16+ ions which initially have no K shell holes interact with the surface. Secondly, if there are more than 2 M shell vacancies at the initial time, strong Mαα two-electron-one-photon (TEOP) transitions are found in the collisions of Xe 28+,29+,30+ ions with the surface.

The X-rays induced during interaction of highly charged argon ions with a beryllium surface are reported. It is found that the K shell X-ray yield of single particle during interaction of hydrogen-like argon ions was 3.6 × 10 −3 , which is five orders more than that of helium-like argon ions. Moreover, due to the screening the 2s electron, no K X-ray was emitted during interaction of lithium-like argon ions with the beryllium surface. It is also found that the X-ray spectrum induced by Ar 17+ interacting with residual gases is very different from that induced by Ar 17+ interacting with the surfaces, that provided an experimental evidence for the existence of the hollow atoms below the surface.

The dependence of the ratio R-1 for transfer ionization to single capture for Cq+, Nq+, Oq+, Neq+ ions on Ne target upon the electronic structure of the projectile is studied by using position sensitive and time-of-flight techniques. It is found that for A(q+)-Ne collisions the ratio R-1 decreases as the atomic number of the projectile increases for q = 4, 5, 6, 7 sequences which differs' markedly from the results we obtained for A(q+)-Ar collisions. The difference is explained by using a statistical model and the orbital penetration picture. Comparison of the R-1 ratios of A(4+)-Ne and A(4+)-Ar collisions provides strong evidence for the increase of the binding energy of the target valence electron after single electron capture. The increase in binding energy depends both upon the atomic number of the projectile Z(1) and the target atom Z(2). The larger Z(1), the larger the increase in binding energy, while the larger Z(2), the smaller the increase in binding energy. (C) 2004 Published by Elsevier B.V.

We made an experimental study on ion guiding through capillaries in uncoated Al2O3 membranes using a variety of ions such as O1+, O3+, and O6+. The incident energy was varied within the range of 30-150 key. The results were compared with others using coated PET and Al2O3 capillary membranes as well as with the so-called scaling law discovered by Stolterfoht and his co-workers. Good agreement of our results with the scaling law was found. However, our membranes showed extraordinarily strong guiding ability. The reason lies in that our membranes were uncoated. A slower charge drift speed along the insulating capillary wall and a much larger equilibrium charge Q(infinity) seems to exist in our experiment. (c) 2010 Elsevier B.V. All rights reserved.

A simple model has been developed within the independent-particle model (IPM) based on the Bohr–Lindhard model and classical statistical model. Cross sections for transfer ionization of helium by ions A q + ( q = 1–3) are calculated for impact energies between 10 and 6000 keV/u. The calculated cross sections are in good agreement with the experimental data of helium by He (1–2)+ and Li (1–3)+ .

The single ionization (SI) and double ionization (DI), single and double ionization accompanying one electron loss (SS) of the projectile and the single and double electron capture of the projectile from target atom are investigated for 2.0–8.0 MeV Naq+–He and C1q+–He collisions. The cross-section ratio of the double ionization (DI) to that of the SI, the ratio of SS+DI to SS+SI, and ratio of double capture (DC) cross-section to that of single capture (SC), are measured by means of time-of-flight technique. The velocity and charge state dependences of the measured cross-section ratios are studied and discussed. The obtained capture cross-section ratios are compared with the theoretical calculations using the classical over-barrier model.

The cross section ratios of the double, triple and quadruplicate ionization to the single ionization of argon were measured by 1.5–7.5 MeV partially stripped oxygen ion (q = 1–4) bombardment. The Auger and the charge exchange processes are discussed and subtracted from the total multiple ionization ratios in order to study the mechanism of the direct multiple ionization of argon by partially stripped ions in the present energy range. It is found that the obtained ratios of the multiple ionization cross sections to those of the direct single ionization of argon agree well with the (νqeff)−2n+2 law for 1.5–7.5 MeV Oq+ (q = 1–4) impinging ions.

The double to single ionization cross section ratios of helium by partially stripped carbon ions have been measured for projectile charge states ranging from +1 to +4 and impact energies from 1.5 to 7.5 MeV. The effective charge effect in partially stripped ion-helium collision is presented. It is found that the effective charge qeff increases as the impinging energy increases and qeff shows a modest dependence upon the projectile charge state in the present energy range. The projectile charge state, projectile and target electronic state dependences of the effective charge effect is discussed using orbital interpenetrating. The nCTMC calculations were carried out to investigate the energy dependence of the effective charge. By introducing effective charge the cross section ratio of helium obtained in the present work is in good agreement with the ( V q eff ) −2 law.

The L X-rays of 71 Lu, 73 Ta and 79 Au were produced by 1.5–4.5 MeV alpha particle bombardment. The emitted L α , L γ1 and L γ2,3 lines were selected to convert X-ray production cross sections into ionisation cross sections. The ionisation cross sections obtained were compared with the predictions of the ECPSSR theory. A reasonable agreement of L 3 -subshell ionisation cross sections between the present experiment and the ECPSSR theory is found. The departures of the measured L 2 -subshell ionisation cross sections from the ECPSSR theory are discussed.

Multiple ionization in collisions of 170 MeV S9+ ions on Ar target atoms was investigated by using time-of-flight (TOF) technique. The charge state distribution of the recoil ions produced in the collisions were determined by the coincident TOF between the projectiles and the recoil ions. The relative recoil ion productions were extracted and compared with the theoretical calculations of n-body classical trajectory Monte Carlo methods.