Search NASA⌕ Search

SEARCH · Search NASA

Results for “PROJECTILES”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
DOE OSTI2010

Tracing multiple scattering patterns in absolute (e,2e) cross sections for H{sub 2} and He over a 4{pi} solid angle

Absolutely normalized (e,2e) measurements for H{sub 2} and He covering the full solid angle of one ejected electron are presented for 16 eV sum energy of both final state continuum electrons. For both targets rich cross-section structures in addition to the binary and recoil lobes are identified and studied as a function of the fixed electron's emission angle and the energy sharing among both electrons. For H{sub 2} their behavior is consistent with multiple scattering of the projectile as discussed before [Al-Hagan et al., Nature Phys. 5, 59 (2009)]. For He the binary and recoil lobes are significantly larger than for H{sub 2} and partly cover the multiple scattering structures. To highlight these patterns we propose a alternative representation of the triply differential cross section. Nonperturbative calculations are in good agreement with the He results and show discrepancies for H{sub 2} in the recoil peak region. For H{sub 2} a perturbative approach reasonably reproduces the cross-section shape but deviates in absolute magnitude.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2010

Laser-assisted positron-impact ionization of atomic hydrogen in the second Born approximation

We study positron-impact ionization of atomic hydrogen in the presence of a linearly polarized laser field in the second Born approximation. The state of the fast incident positron is described by the Volkov wave function and the dressed state of the ejected electron and ground-state hydrogen are treated as a first-order time-dependent perturbative wave function. We calculate the triple differential cross section in the Ehrhardt asymmetric geometry, and numerical results indicate that the second-order effects are significant. Compared with the ionization process by electrons, the influence of the projectile charge sign appears: the binary peaks are greatly enhanced for positrons in the second Born approximation.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2010

Out-of-plane (e,2e) angular distributions and energy spectra of helium L = 0,1,2 autoionizing levels

Angular distribution and spectral (e,2e) measurements are reported for the helium autoionizing levels (2s{sup 2}){sup 1}S, (2p{sup 2}){sup 1}D, and (2s2p){sup 1}P. A special out-of-plane geometry is used where the ejected electrons are emitted in a plane perpendicular to the scattered electron direction. The kinematics are chosen so that this plane contains the momentum-transfer direction. While the recoil peak almost vanishes in the angular distribution for direct ionization, it remains significant for the autoionizing levels and exhibits a characteristic shape for each orbital angular momentum L=0,1,2. A second-order model in the projectile-target interaction correctly reproduces the observed magnitudes of the recoil peaks, but is a factor of 2 too large in the central out-of-plane region. Observed (e,2e) energy spectra for the three resonances over the full angular range are well reproduced by the second-order calculation. Calculations using a first-order model fail to reproduce both the magnitudes of the recoil peaks and the spectral line profiles.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2010

Charging of insulators by multiply-charged-ion impact probed by slowing down of fast binary-encounter electrons

The interaction of ion beams with insulators leads to charging-up phenomena, which at present are under investigation in connection with guiding phenomena in nanocapillaries with possible application in nanofocused beams. We studied the charging dynamics of insulating foil targets [Mylar, polypropylene (PP)] irradiated with swift ion beams (C, O, Ag, and Xe at 40, 23, 40, and 30 MeV/u, respectively) via the measurement of the slowing down of fast binary-encounter electrons. Also, sandwich targets (Mylar covered with a thin Au layer on both surfaces) and Mylar with Au on only one surface were used. Fast-electron spectra were measured by the time-of-flight method at the superconducting cyclotron of Laboratori Nazionali del Sud (LNS) Catania. The charge buildup leads to target-material-dependent potentials of the order of 6.0 kV for Mylar and 2.8 kV for PP. The sandwich targets, surprisingly, show the same behavior as the insulating targets, whereas a single Au layer on the electron and ion exit side strongly suppresses the charging phenomenon. The accumulated number of projectiles needed for charging up is inversely proportional to electronic energy loss. Thus, the charging up is directly related to emission of secondary electrons.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

State-selective electron capture in {sup 3}He{sup 2+} + He collisions at intermediate impact energies

In this work we have measured single-electron capture in collisions of {sup 3}He{sup 2+} projectiles incident on a helium target for energies of 13.3-100 keV/amu with the cold-target recoil-ion momentum spectroscopy setup implemented at the Centro Atomico Bariloche. State-selective single-capture cross sections were measured as a function of the impact energy. They were found to agree with previous existing data from the Frankfurt group, starting at the impact energy of 60 keV/amu; as well as with recent data, at 7.5 keV/amu, from the Lanzhou group. The present experimental results are also contrasted to the classical trajectory Monte Carlo method with dynamical screening.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Single-electron-capture processes in collisions of He{sup 2+}, Li{sup q+} (q=1,2,3), C{sup 6+}, and O{sup 8+} ions with helium

Cross sections for single-electron capture in collisions of He{sup 2+}, Li{sup q+} (q = 1,2,3), C{sup 6+}, and O{sup 8+} ions with helium atoms at incident energy ranging from 50 to 5000 keV/amu have been calculated in the framework of four-body boundary-corrected continuum intermediate state (BCCIS-4B) approximation in both prior and post forms. In this formalism, distortion in the final channel related to the Coulomb continuum states of the projectile ion and the active electron in the field of residual target ion are included. In all cases, total single-electron-capture cross sections have been calculated by summing over all contributions up to n = 3 shells and subshells, respectively. It has been observed that the contribution of the capture cross section into the excited states is significant for asymmetric collision (Z{sub P}>Z{sub T}) and is insignificant for symmetric collision. Numerical results for the total cross sections show good agreement with the available experimental findings, particularly in the post form. Post-prior discrepancy has been found to be within 30% except for Li{sup +} + He interactions below 150 keV/amu.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Differential cross sections for single ionization of H{sub 2} by 75-keV proton impact

We have calculated triply differential cross sections (TDCS) and doubly differential cross sections (DDCS) for single ionization of H{sub 2} by 75-keV proton impact using the molecular three-body distorted-wave-eikonal initial-state (M3DW-EIS) approach. Previously published measured DDCS (differential in the projectile scattering angle and integrated over the ejected electron angles) found pronounced structures at relatively large angles that were interpreted as an interference resulting from the two-centered potential of the molecule. Theory treating H{sub 2} as atomic H multiplied by a molecular interference factor only predicts the observed structure when assumptions are made about the molecular orientation. Here we apply the M3DW-EIS method, which does not rely on such an ad hoc approach, but rather treats the interference from first principles.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Attosecond timing the ultrafast charge-transfer process in atomic collisions

By solving the three-dimensional, time-dependent Schroedinger equation, we have demonstrated that the ultrafast charge-transfer process in ion-atom collisions can be mapped out with attosecond extreme uv (xuv) pulses. During the dynamic-charge transfer from the target atom to the projectile ion, the electron coherently populates the two sites of both nuclei, which can be viewed as a 'short-lived' molecular state. A probing attosecond xuv pulse can instantly unleash the delocalized electron from such a ''transient molecule,'' so that the resulting photoelectron may exhibit a ''double-slit'' interference. On the contrary, either reduced or no photoelectron interference will occur if the attosecond xuv pulse strikes well before or after the collision. Therefore, by monitoring the photoelectron interference visibility, one can precisely time the ultrafast charge-transfer process in atomic collisions with time-delayed attosecond xuv pulses.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Classical treatment of ion-H{sub 2}O collisions with a three-center model potential

We present calculations of cross sections for one- and two-electron processes in collisions of H{sup +}, He{sup 2+}, and C{sup 6+} with water molecules in the framework of the Franck-Condon approximation. We employ an independent-electron method and a classical trajectory Monte Carlo approach. Anisotropy effects related to the structure of the target are explicitly incorporated by using a three-center model potential to describe the electron-H{sub 2}O{sup +} interaction. We derive scaling laws with respect to the projectile charge. We also estimate cross sections for molecular fragmentation subsequent to electron removal.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Charge transfer in collisions of the effectively-one-electron isocharged ions Si{sup 3+}, C{sup 3+}, and O{sup 3+} with atomic hydrogen

In a recent paper [Phys. Rev. A 77, 064702 (2008)], Bruhns et al. reported on an experimental investigation of charge transfer in collisions of Si{sup 3+} ions with atomic hydrogen and compared the energy dependence of the transfer cross sections with published theoretical results and with earlier experimental results for other effectively-one-electron isocharged ions, including C{sup 3+} and O{sup 3+}. These authors observe that these three ions all have the structure of a single electron outside a closed subshell and thus might be expected to behave similarly. However, their results show quite different behavior, and they conclude that the influence of quantum-mechanical effects from the ionic core is clearly seen. We have investigated theoretically three collision systems, Si{sup 3+}, C{sup 3+}, and O{sup 3+} with atomic hydrogen, at projectile energies up to 10 keV/amu using the method of electron nuclear dynamics (END). In this paper we want to clarify and describe in some detail these quantum-mechanical effects by showing the time-dependent dynamics of the electrons during the collision of these three ions with atomic hydrogen. Total charge transfer cross sections were calculated for all three ions and compared with other theoretical and experimental results, showing good overall agreement. With this validation of the END description of the processes, we analyze the details of the computed dynamics of the electrons in each of the processes and illustrate the different mechanisms underlying observed differences in reaction outcomes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

C{sub 60} fragmentation in charge-changing collisions with slow Au{sup +} ions

We investigated ionization and fragmentation of C{sub 60} in the charge-changing collisions of 2.0 keV/amu Au{sup +} ions with C{sub 60} molecules. We performed simultaneous measurements of product ions, the number of secondary electrons, and a charge-selected outgoing Au projectile. The production of C{sub 60}{sup +} ions was predominant in the single-electron capture (1-capture) process. In contrast, multifragmentation of C{sub 60} was predominant in the single-electron loss (1-loss) process. The multifragmentation was enhanced in the 1-loss process compared with the 1-capture process when the same number of electrons was emitted from C{sub 60}. This enhancement was also observed when a fast Si ion traveled close to a carbon nucleus [T. Majima et al., Phys. Rev. A 74, 033201 (2006)]. The 1-loss process of slow Au{sup +} ions is considered to occur closer to a carbon nucleus than does the 1-capture process. Multifragmentation of C{sub 60} is caused by internal electronic excitation although it is probably assisted by nuclear stopping when, at least, the electronic excitation of C{sub 60} is small.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Hydrogen-anion formation near a (2x1)-reconstructed Si(100) surface: Substrate-electronic-structure and trajectory dependence

We calculated the yield of outgoing hydrogen negative ions after the reflection of 1-keV neutral hydrogen atoms from a (2x1)-reconstructed Si(100) surface. We find that the charge-transfer dynamics at the reconstructed surface is dependent on both the surface-electronic structure and orientation of the projectile trajectory relative to the crystal azimuthal directions. Our results are in good quantitative agreement with the measured H{sup -} fractions of Maazouz and Esaulov [Surf. Sci. 398, 49 (1998)] for scattering trajectories that are aligned perpendicularly to rows of silicon dimers.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Slowing down of fast electrons as probe for charging and decharging dynamics of ion-irradiated insulators

The slowing down of fast electrons emitted from insulators [Mylar, polypropylene (PP)] irradiated with swift ion beams (C, O, Kr, Ag, Xe; 20-64 MeV/u) was measured by the time-of-flight method at LNS, Catania and GANIL, Caen. The charge buildup, deduced from both convoy- and binary-encounter electron peak shifts, leads to target material-dependent potentials (6.0 kV for Mylar, 2.8 kV for PP). The number of projectiles needed for charging up (charging-up time constant) is inversely proportional to the electronic energy loss. After a certain time, a sudden decharging occurs. For low beam currents, charging-up time, energy shift corresponding to maximum charge buildup, and time of decharging are regular. For high beam currents, the time intervals become irregular (chaotic).

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Ionization and fragmentation of polycyclic aromatic hydrocarbon clusters in collisions with keV ions

We report on an experimental study of the ionization and fragmentation of clusters of k polycyclic aromatic hydrocarbon (PAH) molecules using anthracene, C{sub 14}H{sub 10}, or coronene, C{sub 24}H{sub 12}. These PAH clusters are moderately charged and strongly heated in small impact parameter collisions with 22.5-keV He{sup 2+} ions, after which they mostly decay in long monomer evaporation sequences with singly charged and comparatively cold monomers as dominating end products. We describe a simple cluster evaporation model and estimate the number of PAH molecules in the clusters that have to be hit by He{sup 2+} projectiles for such complete cluster evaporations to occur. Highly charged and initially cold clusters are efficiently formed in collisions with 360-keV Xe{sup 20+} ions, leading to cluster Coulomb explosions and several hot charged fragments, which again predominantly yield singly charged, but much hotter, monomer ions than the He{sup 2+} collisions. We present a simple formula, based on density-functional-theory calculations, for the ionization energy sequences as functions of coronene cluster size, rationalized in terms of the classic electrostatic expression for the ionization of a charged conducting object. Our analysis indicates that multiple electron removal by highly charged ions from a cluster of PAH molecules rapidly may become more important than single ionization as the cluster size k increases and that this is the main reason for the unexpectedly strong heating in these types of collisions.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Ion-induced triple fragmentation of CO{sub 2}{sup 3+} into C{sup +}+O{sup +}+O{sup +}

Dissociation of CO{sub 2}{sup 3+} formed in fast, heavy-ion-induced ionization of CO{sub 2}, using 5 MeV u{sup -1} Si{sup 12+} ions as projectiles, has been studied by the technique of multi-ion coincidence momentum imaging. From the momentum correlation between the ejected ions, we conclude that dissociation of CO{sub 2}{sup 3+} into C{sup +}+O{sup +}+O{sup +} is a concerted process involving linear and bent conformations of CO{sub 2}{sup 3+}. The kinetic-energy-release spectrum of the dissociation channel CO{sub 2}{sup 3+}{yields}C{sup +}+O{sup +}+O{sup +} is measured and the possible excited states of CO{sub 2}{sup 3+} are computed ab initio.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Calculations of electronic excitation by protons and alpha particles in silicon

This paper presents an ab initio method of calculating the valence electron contribution to the stopping and interaction cross sections of swift ions in matter using linear response calculations of the dielectric function in crystals. We estimate the contribution to the stopping and cross sections by repeated electron capture and stripping of the projectile ion by the medium. We also predict the electronic stopping of protons and alpha particles in silicon and compare to measured values. The predictions generally agree with the data at ion speeds greater than 1 atomic unit. We find that electron capture and stripping is at most a small contribution to the stopping for both ions studied.

electron excitation, silicon, nuclear interactions↗
DOE OSTI2018

Time-dependent orbital-free density functional theory for electronic stopping power: Comparison to the Mermin-Kohn-Sham theory at high temperatures

Electronic stopping power in warm dense matter can affect energy transport and heating in astrophysical processes and internal confinement fusion. For cold condensed matter systems, stopping power can be modeled from first-principles using real-time time-dependent density functional theory (DFT). However, high temperatures (10's to 100's of eV) may be computationally prohibitive for traditional Mermin-Kohn-Sham DFT. New experimental measurements in the warm dense regime motivates the development of first-principles approaches, which can reach these temperatures. Here, we have developed a time-dependent orbital-free density functional theory, which includes a novel nonadiabatic and temperature-dependent kinetic energy density functional, for the simulation of stopping power at any temperature. The approach is nonlinear with respect to the projectile perturbation, includes all ions and electrons, and does not require a priori determination of screened interaction potentials. Finally, our results compare favorably with Kohn-Sham for temperatures in the WDM regime, especially nearing 100 eV.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Electronic stopping power of protons and alpha particles in nickel

The electronic stopping power of nickel for protons and alpha particles at velocities below and around the Fermi velocity has been obtained to high accuracy using time-dependent density functional theory. For the wide range of projectile velocities considered, we observed di erent regimes of electronic stopping due to the alternative participation of s- and d-band electrons. Despite the sharp discontinuity in the electronic density of states near the Fermi energy characteristic of the nickel band structure, we do not nd an anomalous non-linear electronic stopping power limit as a function of velocity. However, we nd a crossover region above v = 0:15 a:u: both for protons and alpha particles, related to the increase in participating host electrons and, in the case of alpha particles, to an increase of the charge state. We compare our calculated results with widely available experimental data and analyze the low velocity limits in the context of Lindhard's linear response theory and previous non-linear density functional calculations. The comparison shows good accord with the lowest velocity experiments available. This may indicate that the adiabatic local density approximation is already a good theory to calculate electronic stopping power in materials at low velocity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗