Projectile Excitation Research Articles

Excitation cross sections of Li +(1s nl) 3L, 1L states in collisions of Li + with He

We report for the first time specific (1s nl) 1L and 3L projectile excitation cross sections of 280 keV ( v=1.26 a.u.) Li ++He collisions. Strong production of triplet states is observed in the (1s nl) distribution of the Li II Rydberg states. We suggest that final state singlet-triplet mixing of the Rydberg manifold in conjunction with cascade repopulation may considerably modify the population of high spin states.

Interactions of energetic gold nuclei in nuclear emulsions.

The nuclear interactions of $_{{\mathrm{}}^{1}{\mathrm{}}_{79}^{97}}\mathrm{Au}$ nuclei of initial energy 990 MeV/nucleon have been studied in nuclear emulsions as they slow down and stop. Typically, these interactions are fragmentations of the incident nucleus into an average of 2.0\ifmmode\pm\else\textpm\fi{}0.3 fragments with Z\ensuremath{\ge}3 and 4.2\ifmmode\pm\else\textpm\fi{}0.2 helium nuclei. As many as eight Z\ensuremath{\ge}3 fragments or 22 helium nuclei have been observed to be produced in a single interaction. The dependence on incident energy and target nucleus is discussed. Some 7% of the interactions appear to be fission in flight of the excited projectile nucleus emerging from the interaction, with the release of two highly charged fragments that contain most, if not all, of the incident charge. The charge distribution of these fragments ranges from symmetric to highly asymmetric.

The dynamically induced spin-orbit interaction of the [formula omitted] projectile

The dynamically induced spin-orbit (SO) interaction of the 19 F projectile is investigated with the coupled channel method including the projectile excitation of the t + 16 O cluster states. By solving the scattering of 19 F from 28 Si , it is found that as large an SO potential as was suggested phenomenologically is not produced within the present calculation.

Mutual excitation of 32S + 28Si at 90 and 97.09 MeV

The mutual excitation of projectile and target was measured for 32S + 28Si scattering at 90 and 97.01 MeV on a large angular range. A coupled channel analysis of the angular distributions is in good agreement with the data. It is used to demonstrate the important interference of simultaneous and sequential excitation amplitudes and the sensitivity of this process to the nuclear surface shape.

Electron capture into excited projectile states in 6-100 keV Ne4+-Ne collisions

The collision system Ne4+-Ne has been studied both theoretically and experimentally. The cross section for one-electron capture into Ne3+ (3s,3p) subshells has been determined in the velocity range 0.1-0.5 au by measuring the VUV photons emitted by these excited states. Quasimolecular diabatic two-electron 1 Sigma g states were calculated in a wide range of internuclear distances. The interaction between crossing diabatic states was obtained by calculating adiabatic splittings in the two configuration approximation. The cross sections for one- and two-electron capture into 3s,3p subshells were calculated using a multichannel Landau-Zener model. Good agreement exists between experimental and theoretical results for one-electron capture.

One- and two-particle inclusive distributions in pion- and proton-nucleus interactions at 300 GeV

We report the data on 300 GeV pion-emulsion-nucleus reactions and compare the results to proton-emulsion-nucleus reactions at the same energy. In particular we present results on the one- and two-particle inclusive pseudorapidity distributions. Two-particle distributions are investigated by using the correlation function formalism. The dependence of one-particle inclusive spectra on the projectile and nuclear excitation obeys scaling. Short-range correlations are observed for pairs of charged particles. No differences are observed between the analogous correlations in pion- and proton-nucleus interactions.

Projectile excitation effects on vector polarized 6Li scattering from 28Si and 16O

Scattering of polarized 6Li from 28Si and 16O targets at E lab ∼ 20 MeV is investigated including the effects of projectile excitation. A single folding model, assuming a d + α cluster structure for 6Li, was used consistently for the interactions in the coupled channels calculations. Contrary to existing one-channel calculations the vector analysing powers were found to be generated by the projectile excitation mechanism and not the folding model spin-orbit potential.

Projectile excitation and structure effects in 6Li and 7Li scattering

Polarized 6, 7Li scattering from 58Ni at E c.m. = 13–20 MeV is investigated by coupled-channels calculations including projectile excitation channels. Potentials are obtained by a single-folding procedure assuming an α+d(t) cluster structure for the projectile. All the available data are reproduced by the calculations. Projectile excitation is found to be the dominant effect in the vector analysing power ( iT 11) for elastic scattering. These effects are in the opposite directions for 6Li and 7Li and explain the opposite signs of the measured iT 11 in the two scatterings. The folding-model tensor potential, which is sensitive to the deformation of the projectile, is mainly responsible for the behaviour of the elastic-scattering tensor analysing power. The cluster-model wave functions used in the folding procedure reproduce the measured Q-moments. The Q-moments of both Li isotopes are negative, but the measured tensor analysing powers ( T T 20 have opposite signs. This can be understood in terms of the different surface structure of 6Li and 7Li. Results and discussions for inelastic scattering and for other scattering systems are also given.

Tensor interactions and polarization phenomena in heavy-ion scattering

Elastic and inelastic scattering of 7Li by 58Ni at E lab = 14.2 and 20.3 MeV is investigated theoretically, special emphasis being laid on polarization phenomena. A parameter-independent study shows second-rank tensor interactions to be the main origin of tensor analyzing powers for both elastic and inelastic scattering. Coupled-channel (CC) calculations using cluster-folding interactions which include the tensor terms are found to be successful in reproducing the data for cross sections and vector and tensor analyzing powers, when projectile excitation effects are sufficiently taken into account. Scattering of 6Li by 58Ni at E lab = 20.0 MeV is also investigated by the CC calculation, where successes similar to the 7Li case are obtained in understanding experimental data.

Polarization by selective loss in beam-foil interaction

The loss of electrons from fast hydrogen projectiles receding from the surface of a metallic foil is calculated in OBK approximation. The selectivity of this process with respect to the magnetic sublevels of the excited projectile is investigated. As only unoccupied states of the conduction electrons are involved, with large wave vectors | K| > K Fermi and energy partly above the vacuum level, the anisotropy introduced by the projectile velocity v ⪆ 1 a.u. is reduced: especially the “circular polarization of the loss process” is thus smaller than for the primary process of electron capture by the projectile. A method is proposed to combine the polarization effects of capture and loss in one model. Preliminary results indicate that the circular polarization of the capture is essentially unaffected, whereas the linear polarization at normal incidence tends to be reduced.

The gas-solid density effect for MeV/u ions: Charge changing cross sections and the effective charge

It is commonplace to describe projectile ion charge-state fluctuations within gaseous and solid targets in terms of “charge-changing cross sections”. However the physical meaning of such cross section has been unclear in solids, where a significant proportion of the ions may be in excited states. For the case of a charge-state distribution dominated by fully stripped and one-electron ions, formulae for the charge-changing cross sections are derived in terms of more fundamental cross sections for projectile excitation, ionisation and electron capture. Density effects in the electron loss and capture cross sections, described in an informal way by Bohr and Lindhard, are presented in simple closed form. Quantitative estimates are given for the density effect in the loss cross section for one-electron ions. The results are supported by experimental data for 3 MeV/u C ions in gaseous and solid C targets. The corresponding density effect in the effective stopping-power charge q eff is considered, both for nearly fully stripped ions and for many-electron ions; and is compared with available experimental data for light and heavy ions at MeV/u energies.

Ion Energy-Loss Spectroscopy for the Collisions of Kr+(2PJ) with N2, CO, NO, and O2

Ion energy-loss spectra for 1308 eV Kr + ( 2 P J ) incident on N 2 , CO, NO and O 2 were measured. For all molecules, fine-structure transitions between different J states of the projectile and vibrational excitations of the molecules were observed. In the case of N 2 and NO, the srectra were relatively simple and only the excitations of fundamental vibrations were found. For CO and O 2 , the excitations of the harmonics, v =0→2, were also observed. In addition to these, for CO, the peak due to the process, Kr + ( 2 P 1/2 )+CO( 1 Σ, v =0)→Kr + ( 2 P 3/2 )+CO( 1 Σ, v '=1), was found. For O 2 , the peak due to the electronic excitation in the target, 3 Σ→ 1 Δ , was observed as well as the prominent peak corresponding to the process, Kr + ( 2 P 1/2 )+O 2 ( 3 Σ, v =0)→Kr + ( 2 P 3/2 )+O 2 ( 1 Δ , v '=0).

A Study of Transfer Excitation in F8+ + He, Ne and Ar Collisions

High resolution x-ray spectroscopy has been used to measure F K x rays resulting from the decay of doubly excited two electron states formed during F8+ + He, Ne, or Ar collisions. The energy range spanned by the spectrometer includes the 2s2p(3P) ? 1s2s(3S), 2s2p(1P) ? 1s2s(lS), 2p2(1D) ? 1s2p(1P), 2p2(3P) ? 1s2p(3P) and the 2p2(1S) ? 1s2p(1P) transitions. These states may be formed by nonresonant transfer excitation, in which electron excitation is coupled with electron capture to an excited state, or by resonant transfer excitation, a process related to dielectronic recombination, in which the capture of a loosely bound target electron results in projectile electron excitation. Calculations have been performed to estimate the contribution of each process to the total measured cross section.

Coulomb nuclear interference effects in the elastic and inelastic scattering of16O and18O ions on70Ge

Excitation functions of the elastic and inelastic scattering cross sections of16O and18O nuclei on70Ge have been measured at angles between 45° and 175° and at beam energies from 31.5 to 57 MeV. A DWBA analysis has been performed in which the composite structure of18O has been taken into account according to the approach developed by Landowne and Wolter. Starting from an optical model potential determined from the elastic scattering data in the16O+70Ge channel, a consistent description of the16O+70Ge (2+, 3−) target excitation, the18O+70Ge elastic scattering and18O(2+)+70Ge projectile excitation cross sections near the Coulomb barrier has been obtained.

Electric quadrupole moment of the first excited state of 12C

The static electric quadrupole moment Q 2+ of the first excited state of 12C has been measured using Coulomb excitation of 12C projectiles by a 208Pb target. The result is Q 2+=+6 ±3 efm 2, which indicates a substantial oblate deformation, consistent with most theoretical expectations.

Energy Dependence of Light Particle Emission from Intermediate Energy Heavy Ion Collisions

High energy nucleus-nucleus collisions can provide a unique method of studying nuclear matter at densities and excitations far from the normal ground state. In these collisions a source can be identified with a velocity intermediate between the projectile and target velocities as well as sources that can be associated with decay of excited projectile and target nuclei. The study of light particle spectra (p, d, t and alpha) associated with this intermediate source can provide information on the equation of state of nuclear matter. Results are presented for O and Ne induced reactions on heavy targets ranging in energy from 9 to 800 MeV/nucleon. Analysis of these light particle data in terms of a single moving source model leads to a consistent description of a system in thermodynamic and chemical equilibrium. Extracted d/p and t/p ratios are almost independent of incident energy while the alpha/proton ratio increases dramatically at low bombarding energies.

Effects of tensor interactions and projectile excitations in the scattering of 7Li

The scattering of 7Li by nuclei is investigated by folding-model interactions, assuming 7Li to consist of an α-particle and a triton. For 58Ni targets, effects of tensor interactions which include excitations of 7Li are very important in explaining the measured cross sections and vector and tensor analyzing powers in elastic scattering, where normalizations of the interaction are not necessary.

Study of the beam-foil excitation mechanism using Cl projectiles, 2–10 MeV

We have studied beam-foil excitation of chlorine projectiles by means of optical spectrometry, in the projectile energy range 2–10 MeV. This is a preliminary report, concentrating on the 3p and 3d level excitations in Cl VII (sodium-like chlorine) and in Cl VIII (neon-like chlorine). A discussion of the results is given, and it is concluded that the 3p and 3d levels in Cl VII and Cl VIII are populated by the same mechanism, namely molecular-orbital electron promotions.

Study of the beam-foil excitation mechanism with the use of chlorine projectiles, 2-10 MeV

Beam-foil excitation of chlorine projectiles has been studied by means of optical spectrometry, at projectile energies ranging from 2 to 10 MeV. The relative populations of various levels in Cl V through Cl VIII have been measured as functions of the projectile energy. It is concluded that for Cl VII and Cl VIII, the 3p and 3d terms are populated entirely through molecular-orbital (MO) electron promotions. High-lying levels of these charge states are excited by means of pickup of electrons from the valence band of the solid. Intermediate levels are populated through multiple inner-shell processes as well as from valence-band electron pickup. For Cl V and Cl VI, most of the levels are excited predominantly by pickup of electrons from the valence band. However, for some of the valence-shell levels in Cl VI, fairly strong contributions from MO processes are found at higher projectile energies. No evidence has been observed for direct Coulomb excitation.

Quadrupole moment of the first excited state of 32S

The static quadrupole moment and B(E2; 0 + → 2 +) value for the first excited state of 32S were measured using the reorientation effect in Coulomb excitation of 32S projectiles. Silicon surface barrier detectors were used to detect 32S ions scattered from 208Pb at mean laboratory angles of 90° and 174°, for bombarding energies in the range 122 to 160 MeV. The results for constructive (destructive) interference from the second 2 + state in 32S are QP 2 + = −16.0±2.2 (−13.3±2.2) e·fd 2 and B(E2; 0 + → 2 +) = 292±17 (307±17) e 2·fm 4