Deep-inelastic Heavy-ion Reactions Research Articles

Yrast states in N = 3050Ca and51Sc isotones studied with deep-inelastic heavy ion reactions

Yrast states in N = 3050Ca and51Sc isotones studied with deep-inelastic heavy ion reactions

Hard-to-reach nuclei studied with deep-inelastic heavy-ion reactions

Spectroscopic studies performed with deep-inelastic heavy-ion reactions are reviewed for two regions of neutron-rich nuclei. The identification of $\nu(h_{11/2})^n$ isomers in nearly complete series of Sn isotopes and the resulting systematic of B(E2) values for isomeric transitions is presented and followed by the discussion of shell model states studied in neutron-rich Te isotopes including the new four neutron-hole isomers identified in 130 Te. Yrast spectroscopy studies of nuclei from the doubly magic 208 Pb region are described by outlining the highest spin states observed in the 208 Pb core nucleus. The E3 transitions observed abundantly in yrast decays are discussed within the framework of particle-octupole vibration coupling and the validity of a simple rule connecting energy shifts of octupole states built on one-particle states with the ones observed for two-particle states is demonstrated.

The $\pi h_{11/2}^{-1}\nu i_{13/2}^{-2}$ three-hole isomeric state and octupole core excitation in the 205 Tl nucleus

New high-spin states were identified in the 205Tl isotope produced in deep-inelastic heavy-ion reactions. The expected 29/2 + yrast state and 35/2- isomeric state with 235 ns half-life were located above the 2.6 μs isomer known from previous studies. Above this isomer a 7092 keV level was interpreted as a 41/2 + state arising from the coupling of the octupole vibration of the 208Pb core with the three-hole structure of the 35/2- isomer.

γ-ray spectroscopy of proton neutron-hole nucleus208Bifrom deep inelastic heavy ion reactions

$\ensuremath{\gamma}$ Rays in the $\ensuremath{\pi}{\ensuremath{\nu}}^{\ensuremath{-}1}$ nucleus ${}^{208}\mathrm{Bi}$ have been studied at the Gammasphere using deep-inelastic reactions induced by a $305\ensuremath{-}\mathrm{MeV}{ }^{48}\mathrm{Ca}$ beam on a thick ${}^{208}\mathrm{Pb}$ target. Previously unknown yrast $\ensuremath{\gamma}$-ray cascades above the ${10}^{\ensuremath{-}}$ millisecond isomer in ${}^{208}\mathrm{Bi}$ were identified in cross coincidence with known $\ensuremath{\gamma}$ rays from complementary potassium products. Yrast and near-yrast levels up to 5.6 MeV in ${}^{208}\mathrm{Bi}$ have been located, and they are interpreted in light of earlier charged particle spectroscopy results, and with the help of shell model calculations.

γ-ray spectroscopy of proton neutron-hole nucleus 208Bi from deep inelastic heavy ion reactions

γ-ray spectroscopy of proton neutron-hole nucleus 208Bi from deep inelastic heavy ion reactions

High-spin states in neutron-rich nuclei explored with deep-inelastic HI reactions

The use of deep-inelastic heavy-ion reactions for the spectroscopy of neutron-rich nuclei is discussed. Conclusions from the N/Z equilibration process studies are outlined and examples of spectroscopic results obtained for the neutron-rich spdf shell nuclei, N = 82 isotones and nuclei from the 208Pb region are reviewed.

New results in spectroscopy of light, medium and heavy nuclei produced in deep-inelastic heavy-ion reactions

Gamma spectroscopy studies performed with deep-inelastic heavy-ion reactions are presented. Recent results are reviewed with selected examples from various regions of nuclear chart. This includes neutron-rich nuclei in sdf shells and those located in the close neighbourhood of 68Ni, 132Sn and 208Pb shell model nuclei. Future prospects and limitations of the thick target method are discussed.

Yrast excitations of heavy tin region nuclei

Thick target γγ coincidence measurements have been used to explore the spectroscopy of neutron-rich Z ~ 50 nuclei formed in deep inelastic heavy ion reactions. Yrast isomers in 119Sn, 121Sn and 123Sn have been identified among the products of heavy ion collisions with 124Sn targets 10-15% above the Coulomb barrier, and isomeric decay schemes are reported. For (vh11/2)n seniority-3 states, the observed level energies agree closely with the results of fractional parentage calculations.

Transport equation for deep inelastic heavy ion reactions and fast fission: Exploiting locally harmonic approximations in a multidimensional phase space

The description of deep inelastic reactions and fast fission as stochastic processes requires the numerical resolution of classical transport equations of the Fokker-Planck type for at least five collective variables i.e. in a ten-dimensional phase space. In order to make the collision problem workable when the phase space involved has more than two degrees of freedom, we propose a numerical approximation sticking to the local harmonic approximation (LHA). We solve the set of equations for the second moments of the distribution with the LHA, including small time intervals of frozen spreading of the statistical distribution in cases where the moment expansion breaks down. More elaborate techniques exist, but they are not yet easily practicable in a phase space with more than two degrees of freedom and have never been tested in such cases. The above approximation leads to accurate results in a two-dimensional phase-space problem so that we think that it can be validly applied in a physical problem requiring more collective degrees of freedom.

Constrained-phase-space approach to spin alignment in deep-inelastic heavy-ion collisions

A constrained-phase-space description of equilibrium in the angular momentum degrees of freedom is used to calculate the spin alignment in deep-inelastic heavy-ion reactions. The phase space is constructed by considering the internal degrees of freedom of the excited fragments and the conservation of angular momentum; the constraint which reflects the reaction dynamics is derived from the classical sticking condition. For several cases of mass-asymmetric heavy-ion reactions, the measured alignments are quantitatively reproduced. It is found that the alignment depends most sensitively on the initial angular momentum and on the fragment deformation at separation so that alignment data are useful to determine these quantities. Angular correlations of sequential-fission fragments from deep-inelastic reactions are also calculated. In the considered example, the measured in-plane anisotropy is explained as mainly resulting from the restrictions, imposed by the experimental setup, on the orientations of the orbital angular momenta in the entrance and exit channels.

Sawtooth curve of neutron multiplicity.

Results of detailed calculations which reproduce the sawtooth dependence of neutron multiplicity on fragment mass in nuclear fission are presented. The same sawtooth seems to occur in deep-inelastic heavy-ion reactions when target and projectile are sufficiently unequal. These results support an idea by Whetstone and suggest a method for the inclusion of shell effects which is different from that employed in the scission-point models.

Analytic treatment of the random walk nucleon-exchange mechanism in deep inelastic heavy ion reactions

The influence of the potential energy surface on the nucleon exchange mechanism is studied without solving a Fokker-Planck equation. Instead, this mechanism is treated explicitely as a sequence of random walk transfers. Simple expressions for the first and second moments of mass and charge distributions are derived analytically. Inversely, it is shown that it is possible to extract the number of exchanged protons and neutrons from experimental data. This procedure is used to gain new informations on the reaction mechanism.

Quantum interference and statistical fluctuations in deep-inelastic heavy-ion reactions

Starting from the general multi-channel formulation of the scattering matrix we perform a coarse-grain average of the cross section appropriate for the observed quantities in heavy-ion reactions. We keep full track of the geometrical factors for the coupling of partial waves and channel spin. Relating the diagonal part of the S-matrix product semiclassically to the statistical treatment in terms of phase-space trajectories we are dealing with quantum fluctuations and statistical fluctuations on an even basis. Quantum corrections play a minor role if the underlying statistical model takes effects of the nonthermalized relative motion properly into account. This is true even for small energy losses.

Electron emission and positron production in deep inelastic heavy-ion reactions

Atomic excitations are used to obtain information on the course of a nuclear reaction. Employing a semiclassical picture we calculate the emission of $\ensuremath{\delta}$ electrons and positrons in deep inelastic nuclear reactions for the example of U+U collisions incorporating nuclear trajectories resulting from two different nuclear friction models. The emission spectra exhibit characteristic deviations from those expected for elastic Coulomb scattering. The theoretical probabilities are compared with recent experimental data by Backe et al. A simple model is used to estimate the influence of a threebody breakup of the compound system upon atomic excitations.

Microscopic description of giant resonances in highly excited nuclei

Giant resonances of general multipolarity in highly excited nuclei, which are produced in compound nuclear and deep inelastic heavy ion reactions, are described microscopically in the finite temperature linear response formalism. The linear response function is calculated in the finite temperature (FT) quasi-particle RPA approximation (FT-HFB-RPA) and is based on the corresponding self-consistent quasi-particle basis (FT-HFB). The theory is derived from the small amplitude limit of FT-TDHFB. The inclusion of cranking constraints allows the investigation of giant resonances in nuclei with large intrinsic excitation energy and high spin. A schematic model for the FT-HFB-RPA is developed and applied to the isovector giant dipole resonance in hot spherical nuclei. It is shown that the energy of the resonance depends only weakly on temperature in these systems. The experimentally observed lowering of the giant mode in highly excited nuclei is to be attributed to different effects. The descritpion of resonance damping lies beyond the scope of the random phase approximation. Possible extensions in this direction and qualitative features of the width of giant resonances at finite temperature are discussed.

Multipolarity of statistical γ-rays from f-p shell nuclei produced in deep-inelastic heavy-ion reactions

Measurements of the circular polarization and the angular correlation of γ-rays from highly excited polarized nuclei, produced in 16O+ 58Ni deep-inelastic reactions, indicate a strong quadrupole component in the spectra of statistical γ-decay at E λ >2 MeV. Differences in the anisotropies observed for the 16O+ 58Ni and the 16O+ 48Ti reactions are attributed to the influence of nuclear structure.

The influence of fluctuations on the correlation between exit-channel kinetic energy and entrance-channel angular momentum for heavy ion collisions

The role of fluctuations on the relationship between the exit-channel kinetic energy and the entrance-channel angular momentum in deep inelastic heavy ion reactions has been studied in the equilibrium limit. Two sources of fluctuations are considered: first, the coupling of the orbital motion to thermally excited angular-momentum-bearing modes, and second, the effect of random shape fluctuations at scission.

Angular Correlation of Fast Light Particles and Heavy Ejectiles in Deep-Inelastic Heavy-Ion Reactions

The effect of dispersion around the mean classical path on the angular correlation between promptly emitted ligth particles and heavy ejectiles from deep-inelastic reactions is studied in a simple model. A relation between the asymmetry in the angular correlation about the beam direction and the polarization of the heavy residual is given.

On the spectroscopy of coherent states

The implications and limitations of the model of heavy ion reactions proposed by Broglia, Dasso and Winther are discussed. The main subjects touched upon are a) the role of particle and surface excitations in the nuclear damping mechanisms, b) the importance of quantal fluctuations. The consequences of the partial violation of self consistency implied by the model are assessed by comparing its predictions against the results of TDHF calculations. The model is applied to the analysis of gamma-polarization measurements in coincidence with deep inelastic events, of the sequential fission fragments angular distribution, of inclusive (α, α′) reactions, and of the inelastic excitation of giant resonances. The main result of the model is that very coherent states seem to be excited in deep inelastic heavy ion reactions.

The time dependence of the variances of charge and mass distributions in deep inelastic collisions

Using the method of Langevin we derive an expression which describes the non-linear time-dependence of the variances of the charge and mass distributions in deep inelastic heavy-ion reactions.