Deep inelastic collisions: A classical description with friction and deformation

A simple classical model with frictional forces and deformation degrees of freedom is presented which reproduces the deep inelastic cross sections, angular distributions and energy losses in a wide range of nuclei. A quantitative fit to the fusion cross sections can also be obtained.     

A classical description of deep inelastic collisions

A classical friction model is applied to describe deep inelastic collisions between heavy ions. With only a very few parameters chosen once and for all, a quantitative fit to the existing fusion data as well as the different features of deep inelastic scattering are obtained.     

A new approach to irreversibility in deep inelastic collisions

We use concepts of statistical mechanics to discuss the irreversible character of the experimental data in deep inelastic collisions. A definition of irreversibility proposed by Ruch permits a unified overview on current theories which describe these reactions. An information theoretical analysis of the data leads to a Fokker-Planck equation for the collective variables (excitation energy, charge and mass). The concept of mixing distance can serve as a quantitative measure to characterize the “approach to equilibrium”. We apply it to the brownian motion as an illustration and also to the phenomenological analysis of deep inelastic scattering data with interesting results.     

A theoretical investigation of shell effects in deep inelastic collisions

The relative importance of three different influences of independent-particle shell structure on the nucleon transport process during heavy-ion collisions are discussed. Results of calculations for the 620-MeV⁸⁶Kr +¹⁹⁷Au system are presented.     

Friction coefficients for deep inelastic heavy-ion collisions

The friction coefficients for deep inelastic collisions are re-evaluated microscopically in the framework of the linear response theory, adopting the cutoff procedure of Jensen et al. to take account of lifetime of particle-hole excitations. They have the same order of magnitude as the previous ones with a constant time cutoff parameters.     

Angular-momentum coherence in heavy-ion deep inelastic collisions

It is shown that cross sections describing deep inelastic collisions between complex nuclei can neither be desribed as a coherent nor as an incoherent superposition of partial-wave amplitudes. The number of interfering partial waves increases with the masses of the interacting nuclei and decreases with the interaction time.     

The third particle in deep inelastic collisions

Angular correlations between charged reaction products have been measured for the reaction¹⁴N+²⁷A1 at 70 and 100 MeV. Light particle evaporation from the heavy recoil is shown to be the dominant process. In addition, however fast alphas are observed for all reaction channels. From the three-body kinematics we conclude that these alphas are emitted from the contact zone between the two heavy ions. A comparison of the results forE _Lab=70 and 100 MeV excludes an explanation of this process by the recently suggested “Piston” or “hot-spot” models.     

A one-dimensional statistical model of friction in deeply inelastic heavy ion collisions

We use the semiclassical approximation for the relative motion (which is simplified and taken to be one-dimensional), neglect other collective degrees of freedom, and describe the coupling between relative motion and intrinsic degrees of freedom by a random-matrix model. This leads to an explicit expression for the friction coefficient. Numerical calculations show qualitative agreement with the data.     

A study of deep inelastic hadron-hadron collisions with a large acceptance calorimeter trigger

Large transverse energy cross sections of 300 GeV/c pions and protons on hydrogen have been measured with a segmented calorimeter covering the central rapidity region ?0.88 < y < 0.67 and 2π in azimuth. The selected events show large multiplicities and no jet-like event structure. Processes more complicated than the scattering of two constituents appear to dominate these inelastic collisions.     

Two-photon collisions in deep inelastic lepton-nucleon and lepton-nucleus scattering

We have calculated the μ-pair production via photon-photon collisions in deep-inelastic charged lepton scattering on proton and nuclei, using the equivalent photon approximation. Specific parametrizations were assumed for the proton and the nuclei form factors and the QED photon structure function. Results are given for lepton energies below 300 GeV and virtual photon massesQ ² less than 50 GeV², as functions of the μ-pair mass, the scaling variablex and the electric chargeZ of the hadron target. Using a photon structure function derived from QPM and VDM we also estimate the contribution of γγ collisions to hadron production in these deep inelastic processes.     

Competing scaling laws in deep inelastic hadron collisions

We have investigated the electro-fission of uranium in the energy range from 15 to 40 MeV with electrons and positrons. Bumps in the cross-section ratio σ^?/σ⁺ are explained as E2 admixtures after the onset of higher-chance fission.     

A new isomer in 136 Ba populated by deep inelastic collisions

Excited states in ¹³⁶Ba, populated in deep inelastic collisions by the interaction of 450 MeV ⁸²Se ions with a ¹³⁹La target, have been studied by means of in-beam -ray spectroscopy. A new isomer with has been identified at an excitation energy E_x = 3.357 MeV. The half-life was determined as ns. The extracted B(E2) value is much smaller than those in ¹³²Te and ¹³⁴Xe. This hindrance is investigated by a shell model calculation.Received: 22 September 2003, Revised: 11 November 2003, Published online: 6 April 2004PACS: 21.10.Tg Lifetimes - 23.20.Lv transitions and level energies - 27.60. + j      

Study of deep inelastic collisions within multidimensional dynamical model

Energy, angle, and charge distributions of binary products of the deep inelastic collisions of heavy ions are studied in the framework of a multidimensional dynamical model of nucleus-nucleus collisions based on the Langevin equations. The model is verified on the example of the ¹³⁶Xe + ²⁰⁹Bi system at several above barrier energies.     

Average polarization in deep inelastic collisions of heavy ions

The polarization averaged over many quantal channels is analyzed. The analytical expressions for probability distribution function and average polarization are derived in cases of pure statistical reactions as well as the planar ones.     

Helicity representation for deep inelastic collisions of heavy ions

Quantum-mechanical cross-section for the inelastic collisions characterized by large values of the angular momenta is analysed. For the case of a planar mechanism of the reaction the approximation of the small helicity is drawn.     

Evidence for shape deformations of fragments in deep inelastic collisions

The number and energy spectra of neutrons evaporated by the heavy and light fragments in deep inelastic collisions have been obtained for the system 240 MeV⁴⁰Ar +¹⁹⁷Au. They indicate that at the scission point the deformation energy is a large part of the total excitation energy espe cially for the light fragment. In the last two years, neutron emission has been studied in deep inelastic reactions^1?6. All the results are similar: the incident energy which is lost during the process is transformed into excitation energy of the final fragments and is shared between the two products proportionnally to their masses. This means that the nuclear temperature was uniform in the composite system. The excitation energy equilibration time is really very short since equilibration is achieved after reaction times as small as 10^?22 s^2,6. Moreover, no preequilibrium emission (direct neutrons-) has been observed.