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      

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.     

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 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.     

General approach to deep inelastic scattering

Due to preliminary indications of a possible scaling violation, it is interesting to clarify which of the parton light-cone results are indeed the consequences of a more general scheme. We consider the constraints imposed by the general ideas of duality (absence of exotics in the t-channel) applied to deep inelastic single-particle distributions. This provides a restrictive scheme, although it allows for a larger set of diagrams than that of the parton model. However, in a particular kinematical region where the diffractive component of the total deep inelastic cross section can be neglected, all the algebraic results of the parton model are recovered by this scheme.     

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.     

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 approach to irreversibility from maximum entropy estimation

This paper deals with the study of some irreversible processes like slow heating of a thermodynamic system or of inhomogeneity, i.e. spatially local equilibrium in it, based on the principle of maximum entropy estimation, in a stochastic model.     

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.     

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.     

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.     

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.     

A classical description of deep inelastic collisions with surface friction and deformation

The friction model for heavy ion induced fusion and deep inelastic nuclear reaction is extended to include deformation. Spheroidal deformation and relative motion of the mass centres of the two interacting nuclei are treated as dynamical variables. The radial frictional force has been assumed to be proportional to the rate of change of the separation between the two surfaces instead of the two centres of mass. The friction coefficients remain unaltered. The potential as a function of deformation and separation distance are generated by a single folding procedure. The model is applied to⁴⁰Ar+²³²Th at 379 MeV (Lab) and¹³⁶Xe+²⁰⁹Bi at 1,130 MeV (Lab). In case of the former, the energy loss, which has not been properly accounted for before, is now satisfactorily explained and in the case of the latter the model predicts the absence of fusion in agreement with experiment.     

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.     

Charge-drift and dispersion in deep inelastic collisions in an equilibrium model

First and second moments of the charge distribution for the reaction⁸⁶K +¹⁶⁶Er have been calculated assuming a thermal equilibrium model. The moments are calculated microscopically on the basis of a realistic two-center shell model as a function of distance as well as of excitation energy. The experimentally observed constancy of the first moments is reproduced.     

Bombarding energy dependence of angular momentum transfer in deep inelastic collisions

Measurements of first and second moments of γ-ray multiplicity distributions from deep inelastic collisions of ⁸⁶Kr + ¹⁵⁴Sm are reported. A global systematics of the angular momentum distributions from deep inelastic reactions with projectile masses ? 40 is presented. The average angular momentum is found to depend linearly on the incident channel average angular momentum, while no simple systematics for the second moment appears obvious. In order to illuminate the question whether the angular momentum transfer process reaches statistical equilibrium in deep inelastic collisions, numerical calculations have been performed on two models: a two-sphere classical model including the collective modes of twisting, bending, wriggling and tilting, and a statistical equilibrium Fermi-gas model. The two-sphere classical model is not able to account for the observed second moments, and neither does the Fermi-gas model give an explanation of the deep inelastic multiplicity data.     

Delta electrons: An atomic clock for deep inelastic collisions

We calculate the δ-electron distribution resulting from heavy ion collisions with projectile energies above the Coulomb barrier. It is shown that the life time (Δτ?10^?21s) of superheavy composite systems causes pronounced oscillations in the electron spectrum. The width of the oscillations is found to be ΔE=h/Δτ. This effect can be used to measure nuclear sticking times quite accurately.