Energy loss of light ions in polypropylene absorber foils

The energy loss of Li, C and O ions in polypropylene absorber foils has been measured using 15 UD Pelletron Accelerator facility at Inter University Accelerator Centre (IUAC), New Delhi, India. The actual experiment has been performed in low flux chamber attached to the General Purpose Scattering Chamber (GPSC). These experimental energy loss values have been compared with the computed values based on various empirical/semi-empirical formulations. Some interesting trends have been observed.      

Energy loss of light ions in different carbon compounds

Experimental data on the energy loss of light H, Li, B, and N ions in methane and H and N ions in benzene vapor have been presented for the range of ion energies from 0.01 to 0.6 MeV/nucleon. It has been shown that the energy loss in the compounds does not follow the addition rule for small ion energies, which indicates the necessity of taking into account the chemical bonds of the molecular targets. The deviation from the addition rule has been experimentally found to increase with the nuclear charge of the projectile ion.     

Energy loss by keV ions in silicon

Using silicon photodiodes with an ultrathin passivation layer, the average total energy lost to silicon target electrons (electronic stopping) by incident low energy ions and the recoil target atoms they generate is directly measured. We find that the total electronic energy deposition and the ratio of the total nuclear to electronic stopping powers for the incident ions and their recoils each follow a simple, universal representation, thus enabling systematic prediction of ion-induced effects in silicon. We also observe a velocity threshold at 0.05 a.u. for the onset of electronic stopping.     

Energy loss of heavy ions in carbon foils

The energy loss of Ar, Ti, Kr, Xe, Pb and U ions in the energy range from 0.2 to 1.4 MeV/amu in carbon foils was measured. The results are compared with theoretical and semiempirical estimations.     

Energy loss to resonantly accelerated ions in laser-plasma

A group of non-thermal ions has been observed when 1.06 μm laser radiation is resonantly absorbed by its own self-generated plasma. The ratio between the kinetic energy carried by this ion group and the total kinetic energy of the plasma ions has been measured. From X-ray measurements indirect evidence has been found for modification of the electron energy distribution due to the acceleration of electrons in the resonant longitudinal field. The experimental results are interpreted by a simple theoretical model.     

Energy loss of light ions with allowance for the presence of metastable particles in the ion beam

The change in the average ion charge due to the presence of particles in metastable states in beams of helium-like ions has been studied. The charge distributions and average charges have been calculated for ions with nuclear charges Z = 3?7 and a velocity of 3.65 au in nitrogen. The previously obtained data on the cross sections of loss and capture of electrons by metastable ions and ions in the ground state were used in the calculations. It is shown that the presence of metastable particles in ion beams leads to an increase in the average charge and energy loss for all considered ions.     

Projectile electron loss in collisions of light charged ions with helium

We investigate the single-electron loss processes of light charged ions （Li^1＋,2＋, C^2＋,3＋,5＋, and O^2＋,3＋） in collisions with helium. To better understand the experimental results, we propose a theoretical model to calculate the cross section of projectile electron loss. In this model, an ionization radius of the incident ion was defined under the classical over-barrier model, and we developed ＂strings＂ to explain the processes of projectile electron loss, which is similar with the molecular over-barrier model. Theoretical calculations are in good agreement with the experimental results for the cross section of single-electron loss and the ratio of double-to-single ionization of helium associated with one-electron loss.     

Energy spectra of light ions backscattered from random solids

A scheme for the calculation of energy spectra of ions backscatterred from random solids is proposed for the energy region where multiple collisions dominate. Calculations are performed for light ion bombardment of heavy targets, which is a case of special interest for the plasma-well interaction in fusion reactors. Examples of spectra obtained for protons incident on a Cu target are presented. A maximum in the spectra is found in accordance with measurements. The position of the maximum seems to vary slowly with the initial ion energy.     

Energy loss straggling in collisions of fast finite-size ions with atoms

The influence of ion size on straggling of energy losses by fast partially stripped ions is studied using the nonperturbative approach based on the eikonal approximation. It is shown that such a consideration of collisions of ions with complex atoms can lead to considerable corrections in calculating root-mean-square straggling of energy losses by fast ions compared to the results obtained for point ions. The root-mean-square straggling of energy losses are calculated for bromide and iodine ions in collisions with copper, silver, and aluminum atoms. It is shown that allowance for the size of the electron “coat” of an ion noticeably improves the agreement with experimental data.     

Energy loss of relativistic, multiply charged ions in an electron plasma

A simple equation is derived for calculating the energy loss of a relativistic, multiply charged ion moving in an electron plasma in the region where the Born approximation fails. The contribution of the energy losses from collisions with solitary electrons is calculated using the exact Dirac equation for relativistic Coulomb scattering. Zh. Tekh. Fiz. 68, 9–12 (February 1998)     

Impact-parameter dependence of energy loss in light ions scattering by a gold atom

In the measurement of energy loss Q within the collision parameter interval 0.02 Å ? b ? 0.4 Å a plateau of the curve of Q(b) at b ? 0.1 Å has been revealed which may be associated with the polarization of the electronic shell of a gold atom.     

Energy loss straggling measurements for helium ions in Mylar and polypropylene polymeric foils

In the present contribution, we report results on energy straggling of He ions penetrating Mylar and polypropylene thin polymeric foils. The measurements were performed in the 900–3000 keV incident particle energy range by using the indirect transmission technique developed previously. The experimental straggling data are corrected to consider the roughness effects due to target thickness inhomogeneity. As expected, the roughness contribution to straggling is more important for helium than for proton ions and decreases as the ion energy increases. At low velocities, (<500 keV/amu), the variation of the experimental energy straggling results differs strongly from predictions based on Bohr’s formalism, and with increasing energies, the experimental results approach gradually the Bohr values.     

Asymptotics of the cross section of the electron loss by fast ions in light media

The dependence of the single electron loss cross section on the nuclear charge Z of a projectile and on the nuclear charge Zt of a target atom for fast collisions is studied theoretically using the plane-wave Born approximation and the sum rule. The results of calculations for fast singly and triply charged ions show that the single electron loss cross section increases monotonically as Z and Zt increase. This can be used to interpolate cross sections of processes if there are no experimental data. The results of calculations compare with the experimental and theoretical data of other authors.     

Asymptotics of the cross section for the electron loss by atoms and ions in light media

The dependence of the cross section of electron loss on the nuclear charge Z of a bombarding ion and on the nuclear charge Z _t of a target atom for fast collisions is studied theoretically using the plane-wave Born approximation and the sum rule. The results of calculations show that the cross section of electron loss for fast collisions increases monotonically as Z and Z _t increase, which can be used to interpolate cross sections for the processes for which there are no experimental data.     

Ground-states of light impurities in metals

A straight forward expression to calculate the ground-state energies of light impurties in metals is derived on the basis of the Thomas-Fermi theory of screening. It is tested for position and a good agreement is found with earlier results.     

Screening of light impurities in simple metals

The Kohn-Sham density functional method is used to calculate self-consistent electron densities around H, He and Li impurities in jellium host corresponding to Li, Al and Mg metals. The differences in the density profiles for interstitial and substitutional impurities are investigated. Residual resistivities, relaxation energies and charge transfer in dilute alloys are evaluated.     

Quantum tunneling of light particles in metals

The motion of a particle in a metallic crystal is studied for low temperatures where transitions between adjacent interstitial sites are caused by quantum tunneling. The influence of electrons and phonons on the hopping rate is taken into account by means of a functional integral method. The electronic influence may effectively be described by Ohmic damping which dominates the low temperature behavior of the defect motion. When subsequent tunneling transitions are statistically independent, the diffusion constant is found to obey a power law, D∼T^2K−1, where K depends on the defect-electron interaction. This power law is limited at low temperatures by the effects of phonon excitations. Near the transition between electron and phonon dominated behavior the diffusion constant has a minimum where the precise temperature dependence of the rate depends not only on phonon spectra but also on the processes limiting phonon lifetimes.