Al Collisions Research Articles

Resonant electron capture in atom metal collisions: HAl(111)

Resonant electron capture in fast grazing HAl(111) collisions is studied with a new nonperturbative method, the coupled angular mode (CAM) method. The quantities needed to describe the electron capture, namely the energy position and autodetachment width of the H− negative ion state are determined. This static study, in contrast with an earlier perturbation treatment, is in agreement with data extracted from experimental results on electron capture by Wyputta et al.

Disappearance of flow in intermediate-energy nucleus-nucleus collisions.

The disappearance of transverse collective flow for $^{40}\mathrm{Ar}$${+}^{27}$Al collisions is studied with an improved Boltzmann-Uehling-Uhlenbeck equation. For collisions at impact parameters less than 3 fm, the predicted energy of balance, ${\mathit{E}}_{\mathrm{bal}}$, is very sensitive to the in-medium nucleon-nucleon cross section, but insensitive to the equation of state. At larger impact-parameter collisions, the sensitivities to both the in-medium nucleon-nucleon cross section and the equation of state at subnuclear density becomes comparable. Comparisions with experimental data indicate an in-medium nucleon-nucleon cross section in the range of 25--45 mb.

Ion-induced Auger emission from Si, Al and Al xMg 1−x samples

Angular resolved investigations of Auger atomic lines induced by ion bombarment have been conducted on Si, Al and Al x Mg 1− x samples. It is confirmed, by direct experimental evidence, that the atomic-like Auger emission occurs outside the sample and new transitions are also observed. All main Auger atomic lines exibit large Doppler shifts which can be accounted by a simple binary collision model in which only excitation of primary recoils by violent asymmetric collisions are considered. Under normal Ar + ion incidence doubly excited L 2MM Auger peaks are observed for Al x Mg 1−x samples ( x = 0.25, 0.50, 0.75, 1.0), such peaks are absent in pure Al bombarded under the same conditions, indicating that such excitations are generated by asymmetric MgAl collisions. The results also show an enrichment of Al within the first layers for an Al 0.50Mg 0.50 sample as the bombarding energy is increased. This enrichment can be interpreted in terms of preferential sputtering and segregation effects.

Entrance channel effects and the formation of hot nuclei

With an improved Boltzmann-Uehling-Uhlenbeck code, we have calculated the excitation energies and the angular momenta of heavy composite residues formed in 40 Ar + 27 Al collisions. At E A ⩾35 MeV , the maximum residue angular momenta are predicted to be significantly smaller than the static limits predicted by the liquid drop model. The excitation energy of residues produced in central collisions is predicted to increase with incident energy, reaching a value of about 5–6 MeV/nucleon at E A =40 MeV .

Disappearance of fusionlike residues and the nuclear equation of state.

The cross sections for massive residues from $^{40}\mathrm{Ca}$${+}^{40}$Ca and $^{40}\mathrm{Ar}$${+}^{27}$Al collisions were calculated with an improved Boltzmann-Uehling-Uhlenbeck equation. The calculated residue cross sections decrease with incident energy, an effect which does not appear related to the residue excitation energy. Larger residue cross sections result from calculations with larger in-medium nucleon-nucleon cross sections or with equations of state which are less attractive at subnuclear density. This dual sensitivity may be eliminated by measurements of observables associated with the coincident light particles.

Light fragment emission correlated with large transverse momentum protons in 94 mev/u 16O induced reactions

Angular, multiplicity and velocity distributions as well as azimuthai asymmetries of light fragments ( Z = 1 and 2) correlated with large transverse momentum protons detected at 90° have been measured in 16 O + 27 Al collisions at 94 MeV/u. Data are compared with a model based on the standard high-energy fireball geometry coupled with the Weisskopf theory of evaporation. Reasonable agreement is achieved with the exception of some discrepancies which could arise either from the absence of specific intermediate-energy corrections or from a non-statistical process.

Peripheral Like Interaction Model of Spectator Residue with Central Fireball in High Energy Heavy Ion Collisions

The experimental data of differential cross sections of 80 productions in P+ Au, He+ Au and Ne + Au collisions at high energies are analyzed in terms of the peripheral like interaction model of spectator residue with central fireball. The results show that the interaction between the central fireball and the spectator residue gradually becomes peripheral or diffractive as the projectile energy increases. The study of high energy heavy ion reactions has been pursued for both peripher­ al and central collisions of projectile and target. In central collision there are two parts 1H ) of the interaction region, in one of which the overlapping part of the projectile and the target becomes hot and thermalized at a high temperature (called the central fireball) and subsequently decays by emitting fast nucleons and possibly light fragments. The non-overlapping region (called the spectator residue) being formed simultaneously along with the formation of the central fireball remains cold and promptly decays into relatively large and slow fragments. 3 ),4) In this paper we study the nature of the interaction between the central fireball and the spectator residue and also the fragmentation mechanisms of the spectator residue based on a nova mode1. 5

Surface topography effects on energy-resolved polar angular distributions of electrons induced in heavy ion-Al collisions: Experiments and models

Abstract The influence of the surface topography on the polar angular distributions of secondary electrons emitted in Ar+ (and Xe+)-Al collisions was studied. After each set of experiments, carried out in controlled bombardment conditions, the surface target was viewed by scanning electron microscope. Some models were elaborated to schematize the main structures observed. Under normal incidence, continuum background and Al L23 VV Auger electron polar angular distributions were not modified by the topography and closely followed a cosine law which is that expected from a flat surface for electrons generated inside the crystal. This result was in agreement with the angular distributions calculated taking into account different structured surface models. For Al L23 MM Auger electrons, experimental angular distributions as a function of the emission polar angle Θ, either were near a constant law or followed a decreasing law depending on the irradiation conditions. The N(Θ) curves calculated from the models sh...

Incidence angle and ion energy dependences of absolute Al L 23 Auger yields in Ar +-Al collisions: Experiments and computer simulations

Experiments and computer simulation of Al L 23 absolute Auger yields from single-crystal and polycrystal aluminium targets bombarded by Ar + ions were peformed. From experimental Al Auger Spectra, band-like and atomic-like structures labelled L 23VV and L 23MM respectively can be distinguished. The dependences of these experimental Auger yields on the incidence angle and ionic energy were studied. Comparison with calculated variation laws of Auger yields from 2p excited Al atoms decaying inside the crystal (bulk emission) and from excited sputtered atoms was carried out. The model was set up on the basis of the atomic collision cascade as generated by the MARLOWE code. Reasonable agreement between experimental and calculated results was obtained in taking into account the Auger neutralization process involving electron exchange between metal and sputtered atoms.

Absolute Auger yields in Ar +-Al collisions: Experiments and computer simulations

Experiments and computer simulations of absolute Auger yields in Ar + -Al collisions were performed. Dependence of the experimental Auger yields on the ionic energy and on the incidence angle are in reasonable agreement with the calculated variation laws. For this, a convenient set of model parameters were determined.

Absolute auger yields in Ar + Al collisions: experiments and computer simulations

Experiments and computer simulations of absolute Auger yields in Ar + Al collisions were performed. Dependence of the experimental Auger yields on the ionic energy and on the incidence angle are in reasonable agreement with the calculated variation laws. For this, a convenient set of model parameters were determined.

Angular distributions of secondary electrons emitted in Ar +-Polycrystalline al collisions

Polar angular distributions of secondary electrons emitted from 40 keV Ar +-polycrystalline Al collisions were studied for both Al L 23 Auger electrons and continuum background electrons. For the latter the angular distributions closely follow a cosine law due to the attenuation of the electron flux inside the crystal as a consequence of the inelastic electron mean free path. Such a result gives evidence for an isotropic “source” for these electrons. For Auger electrons, structures superimposed on the monotonic decreasing law, appeared. Their positions are linked to the incident ion beam direction. The experimental L 23M 1M 23 Auger electron angular distributions seem to be an argument in favour of an emission inside the solid or close to the surface (≲ 2 Å).

Angular distributions of secondary electrons emitted in Ar +-polycrystalline Al collisions

Polar angular distributions of secondary electrons emitted from 40 keV Ar+-polycrystalline Al collisions were studied for both Al L23 Auger electrons and continuum background electrons. For the latter the angular distributions closely follow a cosine law due to the attenuation of the electron flux inside the crystal as a consequence of the inelastic electron mean free path. Such a result gives evidence for an isotropic “source” for these electrons. For Auger electrons, structures superimposed on the monotonic decreasing law, appeared. Their positions are linked to the incident ion beam direction. The experimental L23M1M23 Auger electron angular distributions seem to be an argument in favour of an emission inside the solid or close to the surface (≲ 2 A).

Recoil effects on molecular-orbital X-ray spectra in solid targets

Using the work of Lindhard et al. (1963, 1968) on radiation effects of ions penetrating into solids the authors compute recoil effects on molecular-orbital (MO) spectra in solid targets. In symmetric collisions the dominant effect is due to scattered projectile and recoiling target atoms which carry an inner-shell vacancy into subsequent collisions where MO X-rays are emitted. In asymmetric collisions in which the target is the higher Z partner, the dominant effect is due to recoiling target atoms which emit MO X-rays in subsequent multiple-collision processes. The authors apply their expressions to MO X-rays emitted in Ni+Ni and Ne+Al collisions. In the presently available 12-92 MeV Ni+Ni MO spectra recoil effects are too small to be detectable. In 0.3-1.6 MeV Ne+Al MO spectra measured by Knaf and Presser (1974) recoil effects appear at the lower bombarding energies, which agree well with the authors' calculations.

Multiple Production of Quark Jets off Nuclei

The target dependence of jet production at large transverse momentum observed in $\ensuremath{\pi}$-Al collisions can be explained in terms of contamination of double-quark jets. Qualitative explanations are given for the difference between pion- and proton-induced jet production.

Lifetime studies of Ar-2p-vacancies travelling through solids

We report studies on the production of aluminum K X-rays in Ar +Al collisions using varying thicknesses of thin aluminum foils. It is shown that the mechanism for X-ray production involves a double collision. Parameterization of the data allows us to infer the fraction of the argon beam inside the solid with a 2p-vacancy, the cross section for 2p-vacancy production and the average lifetime of the argon 2p-vacancy travelling through a solid. The lifetime may be related to the atomic state or outer electron configuration of the projectile in the foil.

Non-characteristic X-ray emission in NeAl collisions

Al Kα characteristic and non-characteristic X-ray production cross sections in Ne impacting on Al-foils have been investigated for projectile energies 0.4–20 MeV and foil thicknesses 2–400 μg/cm 2. Thin foils were supported on C-substrates. Three effects were found: The Al Kα characteristic X-ray cross section (1) increases with target thickness and (2) increases for a given Al + C foil upon turning the carbon side to the beam. (3) The X-ray spectral contribution from the C-substrate is less intense by a factor 5 than from a lone C-foil of the same thickness. Al(recoil)→Al contributions to the characteristic X-ray are estimated to be 10 2 less intense than Ne→Al contributions.

Lifetimes of multiplet states in one-, two-, and three-electron sulphur ions

Multiplet states in one-, two-, and three-electron sulphur excited in 92-MeV S→Al collisions are resolved with a crystal spectrometer. Lifetimes of these states are determined using the nonproportionality between multiplet X-ray yields and target thickness.

Large-Angle Collisions in an Aluminum Surface Bombarded by 50-keV Argon Ions

The ejection of charged atomic particles from the surface of an Al target during irradiation by 50-keV ${\mathrm{Ar}}^{+}$ ions was studied. At several angles to the incident beam an analysis of emitted ions was performed by electrostatic deflection to a single-particle detector. The spectra show sharp peaks superimposed on a continuum. The peaks correspond to single collisions. From accurate measurements of peak positions, the inelastic energy loss in the Ar on Al collisions is obtained by methods assuming pure single collisions. The values are about 450 eV for the Al recoil peaks at angles from 77\ifmmode^\circ\else\textdegree\fi{} to 50\ifmmode^\circ\else\textdegree\fi{}, and higher values (up to 600 eV) are found for more violent collisions. Variation of the angle which the surface forms to the incident beam did not influence the peak positions. This result supports the single-collision assumption. Absolute measurements of spectral intensities were also performed, and the number of target atoms per ${\mathrm{cm}}^{2}$ that would account for the measured peak intensities was derived by applying generally accepted theoretical scattering cross sections. Typically, single-collision scattering is obtained from target atoms with density comparable to or less than the density in a {100} crystal plane. Theoretical estimates of multiple scattering are used in a discussion of the peak formation. The target was a single crystal, but the surface included an oxygen impurity, and no lattice-directional effect was observed. The continuum is interpreted; the discussion is based on the absolute intensity measurements and on the theory for penetration of heavy ions in the keV region for random distribution of target atoms.

Broadside radar echoes from ionized trails

An approximate method to compute rough estimates of the broadside radar return from axially symmetric ionized gas columns is presented and applied to an illustrative example The method uses a continuum approach and takes into account the electron-neuti al collision frequency and both axial and radial variation of electron density The local reflectivity is determined as a function of axial position along the column, and these values of reflectivity are used, in turn, to obtain radar cross section estimates