Dependence on collision energy of the stereodynamical properties of the 18O + 32O2 exchange reaction

We report a quantum stereodynamical study of the ¹⁸O + ¹⁶O¹⁶O(v = 0, j = 1) → ¹⁸O¹⁶O(v′ = 0, j′) + ¹⁶O oxygen exchange reaction at four different collision energies. We calculated the polarisation moments and generated stereodynamical portraits related to the key vectors involved in this collision process. Ozone complex-forming approaches of reactants are then deduced. The results indicate that different approaches are possible but strongly depend on the collision energy and other parameters of the collision. We also conclude that the reaction globally tends to favour a perpendicular approach with increasing energy.     

Surface and volume contributions to real and imaginary parts of the heavy-ion optical potential

Starting from the Feshbach expression for the optical potential, explicit formulae for the real and the imaginary parts of the optical potential between two heavy ions (HI's) are obtained. They are each composed of a volume and a surface term. The contributions to the volume term are calculated in two nuclear Fermi liquids which flow through each other starting from the realistic Reid soft core nucleon-nucleon (NN) interaction. Since the Fermi surface is formed by two spheres one obtains a complex Brueckner reaction matrix which is approximated by a complex, effective local interaction. It is used in a fully antisymmetrized double folding procedure to obtain the volume terms of the optical potential between the two HI's. The surface contributions are directly calculated in the collision of the two finite HI's. The collective surface vibrations (3^? octupole state and 2⁺, 4⁺ (T = 0) giant resonances for the ¹⁶O?¹⁶O collision) are included as intermediate states. This yields especially an imaginary contribution at the surface which reduces the transparency found with the volume terms alone. The method is applied to ¹⁶O?¹⁶O scattering at 83 and 332 MeV laboratory energy. The local approximations to the real and imaginary parts obtained in this way agree well with phenomenological fits. The surface terms improve the agreement of the differential cross section at 80 MeV where experimental data are available.     

Light charged particles associated with subthreshold neutral pion emission in the16O+27Al reaction

The production ofZ=1 andZ=2 particles associated with neutral pion emission in the¹⁶O+²⁷Al reaction at 94 MeV/nucleon has been studied. Results are compared with previous findings obtained by charged pions in the same collision at the same bombarding energy and with the prediction of a dynamical model based on a numerical solution of the Boltzmann-Nordheim-Vlasov equation.     

Perturbed stationary state approach to nuclear heavy ion collision

In order to treat the nuclear heavy ion collision at low energy, the perturbed stationary state method developed in the atomic collision is extended so as to include the coupling between the internal state and the angular part of the relative motion. It is shown that this method provides a simple interpretation for the molecular resonances observed in the scatterings of ¹²C + ¹²C, ¹²C + ¹⁶O and ¹⁶O + ¹⁶O, and for the induced rotation mechanism during the collision between heavy ions. Also given is the detailed study for the applicability of the perturbation treatment of this method.     

Fragmentation of relativistic heavy ions

The “incoherent droplet model” is used to explain recent experiments on the fragmentation of ¹⁶O during high energy collision with a Be target. In the ¹⁶O rest frame the fragments have a universal iso tropic Gaussian momentum distribution, independent to the masses of the fragments. The half-width of the Gaussian is $\text{〈p〉 (}\text{A}\text{3}{}_{\mathrm{n}}\text{)}$, where, A is the mass number of the nucleus, n is the total number of fragments, and 〈p²〉 is the mean square momentum of individual nucleons in the fragmenting nucleus.     

Decoupling measurements with low-charge oxygen ions recoiling into gas

A decoupling measurement with low-charge oxygen ions recoiling into gas was interpreted using a phenomenological approach. Values for theg-factor of the 3?level of¹⁶O and for the ion-atom collision cross section thus deduced were found to be in good agreement with results of other experiments.     

Proton and α sequential emission in the 16O + 58Ni deep inelastic reaction: A semi-classical approach

The 132 MeV ¹⁶O + ⁵⁸Ni reaction has been experimentally investigated by using coincident charged particle techniques. A closed-form theoretical approach, describing in a simple picture the non-equilibrium component and the evaporative one of the angular correlation between light particles and reaction residues emitted in a peripheral heavy-ion collision, is applied — in the hypotesis of a sequential process — to the (C,N,O)-α and (C,N,O)-p differential multiplicities for the ¹⁶O + ⁵⁸Ni at 8.25 MeV/A deep inelastic collision. From this analysis some reaction mechanism information is deduced.     

Fusion cross section of the 16O + 16O collision

It is shown that the gross structure of the fusion cross section of the ¹⁶O + ¹⁶O collision is well reproduced by a simple coupled channel method including only elastic and inelastic ¹⁶O + ¹⁶O(3^?) channels, as well as the excitation functions of the elastic and total inelastic ¹⁶O + ¹⁶O(3^?) cross sections.     

Velocity dependence of the chemi-ionization of H2O and D2O on impact of 21S and 23S helium atoms

The velocity dependence for the ionization of H₂O and D₂O to form H₂O⁺ and D₂O⁺ in collisions with both 2³S and 2¹S metastable helium atoms has been measured in a crossed molecular beam apparatus using a mechanical velocity-selector on the metastable beam. The cross-sections are found to be proportional to the —n power of the relative collision energy, with n ? 0.4 for both metastable atoms in both gases. The branching ratios H₂O⁺/OH⁺ and D₂O⁺/OD⁺ were both found to be 4.3 for both metastable helium atoms, and to be independent of the relative collision energy.     

Heavy ion collisions in three dimensions by the relaxation-time method

A quantum transport equation with two-body collisions included via a relaxation-time method, earlier applied to two-dimensional (slab) collisions, is now extended to three-dimensional calculations A density matrix is constructed from self-consistent field wave functions and is time-evolved in cartesian coordinates. This dynamical model of the nucleus is applicable at all nonrelativistic energies. The semiclassical limit is discussed. Results are shown for ¹⁶O-¹⁶O collisions between 40 and 200 MeV/A lab energies. Hot spots and conditions for fragmentation are discussed. The threshold for breakup of the compound system formed in a head-on collision lies between 40 and 60 MeV/A lab energies. At these energies, the maximum density-averaged thermal excitation energy is 7 and 10 MeV/A (average temperatures 8 and 11 MeV), respectively, compared with a binding energy of 8 MeV/A. The system does not thermalize completely, and the distribution in momentum space is not quite isotropic when breaking up.     

Deviations from shape-effect relations in the polarization of inelastically scattered heavy ions

Coupled-channels calculations of the collision of ¹⁶O with ¹⁵⁴Sm are performed with strong and weak absorptive potentials. In the former, the polarization tensors t_2q of inelastically scattered projectiles are seen to follow the shape-effect relations while in the latter, strong deviations from these shape relations are observed. It is shown that the adiabatic model, where the centrifugal potentials in different channels are approximated by that corresponding to the total angular momentum, J, is able to reproduce these features. The isocentrifugal approximation which uses an average orbital angular momentum fails to reproduce the deviations. Comparison between the two adiabatic models is presented. We also show how corrections for Coriolis effects may be made.     

Reduction of the Lane-Robson “calculable” reaction theory to standard R-matrix form

General dynamical equations derived from the Lane-Robson calculable reaction formalism are cast into a form amenable to standard R-matrix treatment, permitting the resonance content of the equations to be made explicit. Formulae are given which enable the collision matrix and the amplitudes of physical eigenfunctions to be calculated directly from the R-matrix with or without the isolation of resonance contributions. The present methodology permits a significant reduction of effort in numerical investigations of the energy dependence inherent in dynamical models of the nucleus. The formalism is illustrated by calculational results obtained from a potential model fitted to ¹⁶O + n scattering data.     

Possible mechanisms of fragmentation of 16O nuclei with a momentum of 4.5 GeV/c per nucleon in track emulsions

The angular distributions of doubly charged fragments of ¹⁶O nuclei having a momentum of 4.5 GeV/c per nucleon and interacting with track-emulsion nuclei were studied. The experimental angular distributions of doubly charged fragments of a ¹⁶O nucleus are not described by the statistical model of the fragmentation of nuclei. The possible channels of fragmentation of ¹⁶O nuclei may include ¹⁶O → 2⁸Be → 4α, ¹⁶O → ⁸Be +⁸ Be* → 4α, ¹⁶O → 2⁸Be* → 4α, ¹⁶O → α+¹²C, ¹⁶O → α +¹²C* → α + 3α, ¹⁶O → α +¹²C* → α + pα ⁷Li, ¹⁶O → α +¹²C* → α + 2⁶Li, ¹⁶O → α +¹²C* → α + pt2α, ¹⁶O → Li + B, and ¹⁶O → Li* + B*.     

Transverse momentum distributions of neutral pions from central and peripheral16O+Au collisions at 200A·GeV

The production of neutral pions by the interaction of 200A·GeV p and¹⁶O projectiles with a Au target has been studied in the pseudorapidity range 1.5≦η≦2.1. Transverse momentum spectra have been measured between 0.4 GeV/c and 3.6 GeV/c and their dependence on the centrality of the collision has been investigated. The peripheral-collision spectra display a marked change of slope with a hard component starting at about 1.8 GeV/c, in contrast to central-collision data. The data are discussed in comparison to p+p and α+α data from the ISR.     

Dunham coefficients for seven isotopic species of CO

An extensive work on vibration-rotation spectra in the fundamental ¹Σ⁺ electronic state of CO is reported. More than 30 000 Doppler-limited measurements corresponding to about 8500 transitions of 255 bands of ¹²C¹⁶O, ¹²C¹⁸O, ¹³C¹⁶O, and ¹³C¹⁸O, most of them observed for the first time, have been obtained with a high information Fourier transform interferometer on the sequences Δv = 1, 2, and 3. The highest v and J values are 41 and 93, respectively. Experimental vibrational levels are then well observed up to three fourths of the dissociation energy limit. These accurate infrared wavenumbers, with an additional selected set of all previous measurements, have been simultaneously fitted to the Dunham expression in a weighted nonlinear least-squares calculation covering seven different isotopic species. It significantly improves both the number of parameters (U and Δ) obtained by the best previous work (35 instead of 23) and their corresponding standard deviations. The rms of the fit is equal to 13 × 10^?6 cm^?1 (390 KHz). Calculated wavenumbers from the 35 reduced Dunham and mass-scaling coefficients can then be used as secondary standards, even for transitions involving high v and J values of the various isotopic species. These new parameters should be a convenient and useful tool for several purposes, such as assignment of infrared laser lines and identification of microwave and infrared transitions in astronomical spectra. The Dunham coefficients Y are also reported for ¹²C¹⁶O, ¹²C¹⁷O, ¹²C¹⁸O, ¹³C¹⁶O, ¹³C¹⁷O, ¹³C¹⁸O, and ¹⁴C¹⁶O. These experimentally determined accurate Y should also be useful for further examination of the potential energy and dipole moment formulations.     

Nuclear matter distributions for 16,17,18O from a microscopic analysis of elastic proton scattering

An analysis of 65 MeV elastic proton scattering by ^16,17,18O has been made in terms of a reformulated optical model. Matter distributions for ¹⁷O and ¹⁸O have been obtained relative to ¹⁶O. The results for the rms matter radii are R₁₇?R₁₆ = 0.04±0.03 fm and R₁₈?R₁₆ = 0.35± 0.07 fm.     

Off-shell effects in O

We calculate the binding energy of ¹⁶O for a set of phase-shift-equivalent potentials previously studied in nuclear matter. Off-shell variations of up to 2.8 MeV per particle occur compared with about a 10 MeV per particle variation in nuclear matter. As in nuclear matter calculations a nearly linear relation exists between the variations in the binding-energy results and the wound integral k. We compare the ¹⁶O results with a nuclear matter calculation at the “equivalent” nuclear matter density of k_F = 1.13 fm⁻¹. This “equivalent” density reflects the fact that ¹⁶O has a surface and hence a lower average density than nuclear matter. The ¹⁶O and nuclear matter off-shell variations are comparable once one takes into account the lower average density of ¹⁶O and the suppression of the relative D-wave interaction — also a surface effect. We present a method of computing the correlated wave functions of finite nuclear systems and display such wave functions for ¹⁶O. The correlated wave functions of ¹⁶O and of nuclear matter are strikingly similar for all of the potentials studied.     

Elastic scattering of heavy nuclei and nucleus-nucleus potential with repulsive core

The elastic scattering of ¹⁶O + ¹²C at various collision energies is discussed in the framework of the optical model with repulsive core nucleus-nucleus potential. The cross sections on backward angles are strongly raised due to repulsive core. It is shown by using the near-side/far-side decomposition method that the near-side component of the scattering amplitude mainly contributes to the elastic scattering cross sections on forward and backward angles. The repulsive core of ¹⁶O + ¹²C potential takes place at distances R ≲ 3 fm.