Resonant coherent ionization in grazing ion/atom-surface collisions at high velocities

The resonant coherent interaction of a fast ion/atom with an oriented crystal surface under grazing incidence conditions is shown to contribute significantly to ionize the probe for high enough velocities and motion along a random direction. The dependence of this process on both the distance to the surface and the velocity of the projectile is studied in detail. We focus on the case of hydrogen moving with a velocity above 2 a.u. Comparison with other mechanisms of charge transfer, such as capture from inner shells of the target atoms, permits us to draw some conclusions about the charge state of the outgoing projectiles.     

Experimental electron loss and capture cross sections in ion-atom collisions

This work presents a compilation of experimental data for electron capture and loss cross sections obtained at the Scobeltsyn Institute of Nuclear Physics for neutral atoms and negative and positive ions with nuclear charge Z = 2-36 in collisions with atomic and molecular gases. The charge-changing cross sections are summarized in tables with the reference list attached.     

Electron emission in 10–100 keV H and He grazing ion-surface collisions

We have measured energy distributions of electrons ejected during grazing 10–100 keV H⁺ and He⁺ ions scattering from Si surfaces for a broad range of electron observation angles. The distributions have contributions strongly dependent on the directions of incidence and observation. For observation regions around the specular reflection of the ions we have studied the angular dependence of the electron structure resulting from electron transfer to the continuum of the effective ion potential. Far from the ion scattering plane we have observed the Si Auger electron spectrum. We discuss the differences between the Auger peaks obtained by electron and grazing proton bombardment of Si surfaces partially covered with O₂ and Al.     

Image charge interaction of multicharged ions in grazing collisions with an Al(111)-surface

We study the angular distributions of multicharged noble gas ions after scattering from a clean and a cesiated Al(111)-surface under a grazing angle of incidence. The data show pronounced effects of the image charge attraction on the incident trajectory which allow us to deduce the energy gained by the projectile during the approach towards the surface. We present a detailed discussion of our experimental method and compare the results with an “over-barrier model” describing the neutralization of multicharged ions in front of a metal surface.     

Energy loss of Xe-ions in thin foils

The energy loss of ¹³²Xe-ions in C, Al, Ni, Ag, Lu, Au, Pb and Th foils was measured in the energy range from 0.1 to 5 MeV/u using the TOF-E method. The results are compared with previously published data and with the predictions of several computer codes. They include theoretical codes: PASS, CASP, semi-empirical programs: SRIM, LET and the Hubert table predictions.     

Single electron loss in the collisions of lowly charged ions and atomic hydrogen

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.     

Energy and centrality dependence of light nuclei production in relativistic heavy-ion collisions

We study the energy and centrality dependence of deuteron and triton（helium-3） production in relativistic heavy-ion collisions at the BNL Relativistic Heavy Ion Collider（RHIC） and CERN Large Hadron Collider（LHC）using the Tsallis distribution, blast-wave（BW） model, and stationary Fokker-Planck（FP） solution. Our study shows that good agreement can be reached between the fitting results from the stationary FP solution and the experimental data for Au + Au collisions from the beam energy scan（BES） p...     

Energy loss of degrader in SC200 proton therapy facility

The proton beam energy determines the range of particles and thus where the dose is deposited. According to the depth of tumors, an energy degrader is needed to modulate the proton beam energy in proton therapy facilities based on cyclotrons, because the energy of beam extracted from the cyclotron is fixed. The energy loss was simulated for the graphite degrader used in the beamline at the superconducting cyclotron of 200 MeV in Hefei(SC200). After adjusting the mean excitation energy of the graphite used in the degrader to 76 eV, we observed an accurate match between the simulations and measurements.We also simulated the energy spread of the degraded beam and the transmission of the degrader using theoretical formulae. The results agree well with the Monte Carlo simulation.     

Energy loss of ions interacting with metal surfaces

The problem of calculating the energy loss of ions specularly reflected by metal surfaces is treated. Different approximations for the treatment of the screening and scattering are presented and their validity in the different coupling regimes is discussed. Illustrative comparisons with available experiments are provided.     

Energy loss of protons in carbon nanotubes: Experiments and calculations

We have studied the energy loss of protons in multi-walled carbon nanotube (MWCNT) samples, both experimentally and theoretically. The experiments were done in transmission geometry, using 6 and 10 keV proton beams, with the MWCNT targets dispersed on top of a ～20 nm-thick holey carbon coated TEM grid (amorphous carbon film, a-C). The energy loss of protons interacting with the MWCNTs and the amorphous carbon film is obtained after analyzing the signals coming from both types of carbon allotropes. The electronic energy loss of protons is calculated using the dielectric formalism, with the target energy loss function built from optical data. Comparison of experimental and theoretical data indicates that model calculations appropriate for three-dimensional (bulk) targets substantially overestimate the energy loss to MWCNTs. In contrast, a recent parameterization of the dielectric function of MWCNTs predicts significantly lower stopping power values compared to the bulk models, which is more in line with the present experimental data when considering the additional stopping mechanisms that are effective in the keV range.     

Energy loss of partially stripped ions in pre-equilibrium frozen charge states

The inelastic energy loss of swift single-atom hydrogenlike, heliumlike, and lithiumlike ions, and hydrogen-molecule ions is investigated under charge state pre-equilibrium conditions. During their passage, those charge states are assumed to be frozen. The stopping-power values and the effective charges calculated on the basis of the dielectric function method, the wave-packet method, and the recently derived analytical formula, are compared with existing experimental data.     

Energy loss and straggling of Li ions in the polymer foils

Energy loss and straggling of 0.18-0.78 MeV/amu ⁷Li ions in polycarbonate, polyethylene terephthalate and polypropylene foils were measured by means of a transmission technique with a half-covered detector. The stopping force measurements are compared with the SRIM 2006 calculation and the database of the ICRU report 73. The measured energy loss straggling are in satisfactory agreement with the results yielded using the empirical formula at the higher energy region. The obtained data also demonstrated that the validity of Bragg’s rule applied to stopping force and energy loss straggling for ⁷Li ions in polymer foils.     

Energy loss straggling of Si and Cl ions in polymeric foils

The energy loss straggling has been measured for Si and Cl ions in three polymers viz. Polypropylene PP (C₃H₆), Polyethylene terepthalate PET (C₁₀H₈O₄), Polyethylene naphthalate PEN (C₇H₅O₂), in the energy range ∼1.50 to 4.50 MeV/u. The measured energy loss straggling values have been compared with the corresponding computed values based on Bohr, Lindhard and Scharff, Bethe-Livingston and Yang et al., formulations, in order to check the reliability and validity of these formulations. Further, based on the experimental data, an empirical relation for the calculations of energy loss straggling has been developed. The predicted values from this relation are in close agreement with the experimental data.     

Energy loss calculations for fast light ions in celluloid including charge-exchange processes

A method is proposed to calculate the charge-exchange energy loss (−dE/dx)_ex and electronic energy loss (−dE/dx)_el on the basis of the electron capture and loss cross-sections, extracted from the experimental data. The experimental and calculated results are presented for energy loss of projectile ions Be, B, N and O with 0.35 MeV/nucleon, passing through celluloid films. The dependence of energy loss on the initial charge of projectile ions and target thickness in nonequilibrium conditions is examined.     

Energy loss of 4He ions in AI2O3 and SiO2

From the ⁴He energy loss measurements in Al, Al₂O₃, Si and SiO₂, we have extracted stopping cross sections for “solid” oxygen over the energy range 0.2 to 2 MeV and at 5.48 MeV. Assuming linear additivity of atomic stopping cross sections, values for oxygen are 5.3 to 15% higher in SiO₂ than in Al₂O₃, indicating that discrepancies in the Bragg rule for these oxides are clearly not due to phase effects but to chemical binding effects.     

Energy loss and straggling in LR-115 and Kapton polymeric foils for energetic ions

The energy loss and straggling in LR-115 and Kapton polymeric foils for Li, C, O and Si ions in the energy range ∼1.0-6.5 MeV/u have been measured, utilizing 15 UD Pelletron accelerator facility available at Inter University Accelerator Centre (IUAC), New Delhi, India. The measured energy loss and straggling values have been compared with the corresponding computed values adopting some widely used energy loss and straggling formulations. The aim of such a comparison is to check the reliability and validity of the existing energy loss and straggling formulations.     

Coulombic potentials in atomic collisions

Charge exchange ion-atom collisions are studied. The influence of Coulomb interaction potentials between the charged particles on scattering amplitudes and total cross sections is analysed at asymptotic high impact velocities.     

Energy loss caused by shielding effect of steel cage outside source tube

The energy loss, produced by shielding effect of steel cage outside the source tube, is quite considerable. With PENELOPE software package, MC results have been obtained based on the simulation of different source con- formations. The result illustrates that the naked source tubes can improve the utilization ratio of the cobalt facilities. It demonstrates the applied value of the naked source tube in engineering.