Ne Projectiles Research Articles

Analysis of elastic scattering of 6,7Li and 20Ne from 24Mg nucleus using microscopic potentials

The experimentally available angular distributions (ADs) for [Formula: see text]Li and [Formula: see text]Ne ions elastically scattered from a [Formula: see text]Mg target are reanalyzed using various nuclear potentials based on phenomenological as well as microscopic approaches. The considered data are [Formula: see text] ADs at [Formula: see text], 88 and 240[Formula: see text]MeV; [Formula: see text] ADs at [Formula: see text], 34 and 88[Formula: see text]MeV; and [Formula: see text] ADs at [Formula: see text], 60, 80, 90 and 100[Formula: see text]MeV. Special emphasis is given on the ([Formula: see text]) and ([Formula: see text]) cluster structures of the 6Li and 7Li weakly bound projectiles, which appear at relatively low energies of [Formula: see text] and 2.468[Formula: see text]MeV, respectively. Furthermore, the [Formula: see text]Ne stable nucleus is a candidate to reveal the [Formula: see text]O cluster structure at an energy of 4.73[Formula: see text]MeV. These systems are analyzed within the framework of the cluster folding model by taking into consideration the aforementioned cluster nature of the 6Li, 7Li and [Formula: see text]Ne projectiles. The adopted approaches fairly reproduced the experimental ADs.

A comprehensive theoretical analysis of 22Ne nucleus by using different density distributions, different nuclear potentials and different cluster approach

In this study, a systematic analysis is made on the [Formula: see text]Ne nucleus. First, using different theoretical approaches, we show eight density distributions for the [Formula: see text]Ne nucleus. For there densities, we obtain the elastic scattering angular distributions of [Formula: see text]Ne by [Formula: see text]C and [Formula: see text]C targets. Then, to offer alternative nuclear potentials in explaining nuclear interactions related to [Formula: see text]Ne projectile, we calculate the elastic scattering cross-sections of [Formula: see text]C and [Formula: see text]C reactions by using six different nuclear potentials. Finally, we investigate cluster structures of the [Formula: see text]Ne nucleus via a simple cluster approach. We compare the calculated elastic scattering angular distributions with the experimental data.

Sputtering of Benzene Sample by Large Ne, Ar and Kr Clusters - Molecular Dynamics Computer Simulations

Molecular dynamics simulations are employed to probe the role of an impact angle on emission e ciency of organic molecules sputtered from benzene crystal bombarded by 15 keV Ne2953, Ar2953, and Kr2953 clusters. It is found that both the cluster type and the angle of incidence have signi cant e ect on the emission e ciency. The shape of the impact angle dependence does not resemble the dependence characteristic for medium size clusters (C60, Ar366), where sputtering yield only moderately increases with the impact angle, has a shallow maximum around 40◦ and then decreases. On the contrary, for the large projectiles (Ne2953, Ar2953, and Kr2953) the emission e ciency steeply increases with the impact angle, has a pronounced maximum around 55◦ followed by rapid signal decay. It has been found that the sputtering yield is the most sensitive to the impact angle change for Kr cluster projectiles, while change of the impact angle of Ne projectile has the smallest e ect on the e ciency of material ejection.

Probing elastic and inelastic breakup contributions to intermediate-energy two-proton removal reactions

The two-proton removal reaction from ${}^{28}$Mg projectiles has been studied at 93 MeV/u. First coincidence measurements of the heavy ${}^{26}$Ne projectile residues, the removed protons, and other light charged particles enabled the relative cross sections from each of the three possible elastic and inelastic proton removal mechanisms to be determined. These more final-state-exclusive measurements are key for further interrogation of these reaction mechanisms and use of the reaction channel for quantitative spectroscopy of very neutron-rich nuclei. The relative and absolute yields of the three contributing mechanisms are compared to reaction model expectations based on the use of eikonal dynamics and $sd$-shell-model structure amplitudes.

Ionization in fast atom-atom collisions: The influence and scaling behavior of electron-electron and electron-nucleus interactions

We report cross sections for ionization of He coincident with electron loss from He, Li, C, O, and Ne pro jectiles. For He, Li, C, and O pro jectiles, the cross sections were measured directly, while the Ne cross sections were obtained by transforming results for He pro jectiles colliding with Ne. We find that, at energies of about 100-500 keV/u, neutral pro jectiles can ionize a He target almost as effectively as a charged pro jectile. The contribution to ionization due to electron-electron interactions is found to scale with the number of available pro jectile electrons. Comparing ionization by the bound electrons on projectiles to ionization by free electrons, we find the cross sections for ionization by bound electrons are systematically smaller than those for free electrons.

18Ne diproton decay

Two proton radioactivity studies have been performed on excited states of 18 Ne produced, among other fragments, by 20 Ne projectile fragmentation and excited via Coulomb excitation on a Pb target. Every incoming ion was tagged before interacting with the lead target on an event by event basis in order to discriminate the secondary reactions according to the projectile. Decay of 18 Ne levels has been studied by complete kinematical reconstruction. In spite of the low statistics a couple of events looks very promising for two proton correlated emission.

STRUCTURE OF BARRIER DISTRIBUTIONS: PROBING THE ROLE OF NEUTRON-TRANSFER CHANNELS

In view of its large deformation, which should give rise to strong barrier structures, the 20 Ne projectile has been used to study the influence of neutron-transfer channels on the distribution of barrier heights. A previous experiment with a combination of projectiles 20,22 Ne suggested that the role of α-particle transfer channels is small. By an appropriate choice of targets (90 Zr and 92 Zr ), having very similar intrinsic structures (excited states and deformation parameters) but giving rise to different Q-values for neutron transfers, we highlight the role of these channels.

Comprehensive study of the surface peak in charge-integrated low-energy ion scattering spectra

Low-energy ion scattering is very surface sensitive if scattered ions are analyzed. By time-of-flight (TOF) techniques, the neutral and the charge-integrated spectra (ions plus neutrals) are obtained, which yield information about deeper layers. It is well known that charge integrated spectra may exhibit a surface peak which is more pronounced for heavier projectiles, e.g., Ne ions. Aiming at a more profound physical understanding of this surface peak, we performed TOF experiments and computer simulations for H, He, and Ne projectiles scattered from a polycrystalline copper target. Measurements were done in the range of 1--9 keV for a scattering angle of $129\ifmmode^\circ\else\textdegree\fi{}$ under UHV conditions. The simulations were performed using the MARLOWE code for the given experimental parameters and a polycrystalline target. In the experiments, a pronounced surface peak was observed at low energies, which fades away at higher energies. This peak is quantitatively reproduced by the simulation. Several atomic layers may contribute to the surface peak, depending on the energy. Analyzing the contributions of the individual outermost atomic layers, one finds that the binary collisions of the projectiles with atoms in the first and the second layer yield a narrow energy distribution, while the contribution from the deeper layers is dominated by multiple scattering and therefore exhibits a very broad energy spectrum. It is shown that the appearance of a more or less pronounced surface peak is due to the relative contributions of single scattering and multiple scattering and thus depends on the projectile energy and mass.

Stopping power of a KCl(0 0 1) surface for low energy Ne atoms

Energy losses of specularly reflected ions from a KCl(001) surface at grazing incidence of 15–30 keV Ne+ ions are measured in order to investigate the effect of the large band gap on the surface stopping power for low energy projectiles. The position-dependent stopping power of the KCl(001) surface for Ne projectile is derived from the observed energy losses. Because the direct electron excitation by the projectile–electron collision, which is the dominant stopping mechanism for low energy projectiles at metal or semiconductor surfaces, is almost prohibited at insulator surfaces due to the large band gap, the surface stopping power of the KCl(001) is expected to be much smaller than those of metals or semiconductors. The obtained stopping power is, however, found to be comparable to that of the SnTe(001) surface, which is a typical narrow-gap semiconductor. Charge exchange processes probably make an important contribution to the stopping at the KCl(001) surface for the low energy Ne projectile.

Crystal azimuthal-angle dependence of excited-state production and core-rearrangement processes in Ne+ scattering on Al(111).

We present the results of a study of the azimuthal-angle dependence of ${\mathrm{Ne}}^{**}$ excited-state production in ${\mathrm{Ne}}^{+}$ ion scattering on an Al(111) surface. A strong variation in the intensity of ${\mathrm{Ne}}^{**}[2{p}^{4}(^{3}P)3{s}^{2}]$ and ${\mathrm{Ne}}^{**}[2{p}^{4}(^{1}D)3{s}^{2}]$, and most importantly in their relative intensity, is observed as a function of crystal azimuth. This is interpreted as being due to a change in singlet-to-triplet atomic-core rearrangement of excited scattered Ne projectiles as they move away from the surface. Numerical simulations were performed and these variations in rearrangement rates were assigned to a rapid change in the perpendicular velocity distributions of scattered particles as a function of incidence azimuth. We conclude that nonlocalized atomic rearrangement processes play an important role in the singlet-to-triplet core rearrangement.

Inelastic energy loss and inner-shell electron promotion in low energy Ne ions scattered from Fe and Ni surfaces

Inelastic energy loss and inner-shell electron promotion of Ne + ions scattered from Fe(110) and Ni(100) surfaces have been studied systematically in the energy range from 1 to 7 keV at large scattering angles. The inelastic energy loss shows a threshold-type greater increase with incident energy in both scattering systems. Similar threshold-type behaviour is also observed in the scattered Ne + ion yield, the scattered Ne ++ ion yield and the peak fwhm. The threshold incident energy for such phenomena is found to increase with the atomic number Z of the target. It is suggested that excitations of the Ne 2s electrons occur during the close collision of the Ne with Fe or Ni atoms, resulting in a sudden increase in the inelastic energy loss. The excitation probability is found to depend on the atom position of the target relative to the swapping points of the Ne inner-shell energy levels. The ionization of the doubly excited Ne∗∗ particles alters the charge exchange behaviour of the Ne projectiles on their outgoing trajectories, leading to a remarkable increase in the scattered ion yield. The results show that inner-shell electron excitations could be significant in low energy ion surface scattering and may play an important role in the charge exchange process.

2 keV He and Ne ion scattering on a Cu(110) surface: Experiment vs simulation

Scattering experiments performed at 143° with a TOF-ISS system on a Cu(110) single crystal indicate the very different sampling depth of He ions as compared with Ne ions. The ISS polar scans measured with He ions show a high sensitivity to the bulk atomic rows of the single crystal, whereas the scans measured with Ne ions indicate a sensitivity to only a couple of atoms in the first atomic layers. In order to evaluate the depth sampled by the backscattered particles, ion trajectories have been calculated with the MARLOWE simulation code. With Ne, the simulation shows that backscattered particles arise only from the 4 first layers (5 Å), but with He ions, they come from at least 80 layers (100 Å). A detailed analysis of escaping trajectories indicates that the Ne projectiles are scattered from the first layers after short trajectories. On the other hand, helium trajectories are usually quite complex, due to the possibility to follow privileged directions (channels), so that the projectiles can scatter from deep layers. We see that, even at low energy, channeling may be the major contributor to the variations of the backscattered intensity.

Deexcitation of hollow atoms: autoionization of multiply excited N, O and Ne atoms at a Pt(110) surface

The K-Auger electron emission during the interaction of 60 keV N 6+, 70 keV O 7+ and 90 keV Ne 9+ with a Pt(110) surface occurs below the target surface for glancing angles in the range 10–90°. Therefore the projectile K-Auger electron spectra are distorted by solid state effects. These effects can be removed from the measured spectra by using a procedure originally developped for photoelectron spectroscopy. The resulting primary excitation spectra are compared with results of atomic structure calculations. The analysis reveals that at the instant of K-Auger electron emission on the average five electrons are present in the L-shells of the hydrogen-like N, O and Ne projectiles. Furthermore the ratio of the KLL- and KLM-Auger electron emission yields is determined. It is 3.4, 3.7 and 4.6 in case of the N 6+, O 7+ and Ne 9+ projectile, respectively.

Distortion of two-pion interferometry by multipion correlations.

Multipion correlations arising from the symmetrization of the n-pion wave function affect the extracted information from two-pion correlation measurements. The influence of multipion correlations on a sample of like-pion pairs can be expressed as a multipion correlation factor, the distribution of which offers good sensitivity to the multipion correlation effect. Analyses of the multipion correlation factor for two Bevalac streamer chamber data samples of 2.1A GeV Ne+Pb and 1.8A GeV Ar+Pb collisions show that the multipion correlation effect in the former sample is greater than in the latter. This result mainly arises from the fact that the pion source for Ne projectiles is smaller than for Ar projectiles. The residual correlations in the reference sample are related to the multipion correlation factor in multipion events, which can be expressed as a residual correlation factor. The influence of multipion correlations on two-pion interferometry analyses arises from the ratio of the residual correlation factor to the multipion correlation factor.

Ion-induced desorption of loosely bound oxygen adsorbed on solid surfaces

Abstract We measured the desorption cross section of loosely bound oxygen adsorbed on oxidized magnesium induced by 4 keV He, Ne, Ar and Kr projectiles. We found that this cross section is two orders of magnitude larger than that corresponding to chemisorbed oxygen. We also found that the main contribution to desorption is the knock-off of adsorbed oxygen atoms by sputtered atoms from the substrate. In the case of He an additional mechanism, namely knock-off of adsorbed oxygen atoms by He projectiles reflected in the solid, could help to explain a relatively large desorption cross section.

Investigation of delta -electron emission in collisions of highly charged fast Ne projectiles with carbon-foil targets.

The angle and energy dependence of electron emission following the interaction of 70--170-MeV ${\mathrm{Ne}}^{\mathit{q}+}$ (q=7,10) projectiles with 20 and 100 \ensuremath{\mu}g/${\mathrm{cm}}^{2}$ carbon foils has been investigated experimentally. Absolute emission yields were determined for ejection angles ranging from 0\ifmmode^\circ\else\textdegree\fi{} to 180\ifmmode^\circ\else\textdegree\fi{} and electron energies from 10 eV to 6 keV for normal-incidence ion beams. The experimental \ensuremath{\delta}-electron spectra are compared to results from a newly developed theoretical model based on a separation of energy loss and angular scattering for secondary electrons.

Nuclear collective flow and charged-pion emission in Ne-nucleus collisions at E/A = 800 MeV.

Triple-differential cross sections of charged pions were measured for collisions of Ne projectiles at E/A = 800 MeV with NaF, Nb, and Pb targets. The reaction plane was estimated event by event from the light-baryon momentum distribution. For heavy targets, preferential emission of charged pions away from the interaction zone towards the projectile side was observed in the transverse direction. Such a preferential emission, which is not predicted by cascade calculations, may be attributed to a stronger pion absorption by the heavier spectator remnant.

TRANSFER EXCITATION AND CAPTURE OF INNER TARGET ELECTRONS IN COLLISIONS WITH SLOW MULTIPLY CHARGED IONS

Single electron capture by triply charged Ne projectiles in He and Ne has been studied at low collision energies (600 eV) showing the dominant mechanisms to be due to transfer excitation and capture of inner target electrons. The results are compared with predictions of various classical models and improved multi-channel LZ calculations. Information is obtained on the coupling strenght relevant for both types of processes.

Synthesis and study of atomic nuclei with Z > 100

The studies of atomic nuclei with Z > 100 are closely related to the synthesis of new chemical elements and to the investigation of stability limits for the heaviest nuclides. From the mid-50s these studies have been carried out using intense heavy-ion beams and highly sensitive techniques designed for the physical and chemical identification of rare short-lived nuclei. The studies proceeded in two stages, the first one being characterized by the use of hot-fusion reactions between the U, Pu, Am, Cm and Cf target nuclei and the C, N, O, and Ne projectiles and the second being based on the use of the cold-fusion reactions induced by Cr, Mn, and Fe projectiles on Pb and Bi target nuclei. As a result, the chemical elements with atomic numbers from 102 to 109 have first been synthesized. The radioactive properties of over 40 isotopes of these elements have been investigated and unambiguous evidence has been obtained that shell effects play a decisive role for the stability of the Z ≳ 104 nuclei against spontaneous fission. This provides an experimental substantiation for the known hypothesis that the island of nuclear stability should lie around Z ⋍ 114 and N ⋍ 178 or 184. It has been proposed to synthesize elements with Z ≥ 110 by the complete fusion reactions of uranium and adjacent element nuclei with projectile nuclei such as Ar and Ca. The spontaneous fission of a product nucleus (a total of 26 events) has been observed in Dubna experiments with the 232Th + 44Ca and 236U + 40Ar reactions. The authors of those studies tentatively assigned this activity to the decay of the nuclei of element 110.

Energy-gain spectroscopy of electron-capture collisions between low-energy Ar and Ne projectiles and atomic and molecular deuterium targets

Translational energy-gain spectroscopy is used to determine the final-state (nl) populations following single-electron capture by ${\mathrm{Ar}}^{\mathrm{q}+}$ (q=4--8) and ${\mathrm{Ne}}^{\mathrm{q}+}$ (q=4--7) projectiles in atomic and molecular deuterium targets at an energy of 545q eV. The importance of kinematics in analyzing these systems is discussed. The final-state populations are found to be very sensitive to the energy-level structure of the collision system. The results are interpreted in terms of a ``reaction window'' in the energy gain which is calculated using a multichannel Landau-Zener model.