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Coupled channels calculations of heavy-ion reactions near the Coulomb barrier

Description: A coupled channel treatment of the reaction /sup 58/Ni /plus/ /sup 64/Ni is presented. Angular distributions for ''inclusive elastic'' scattering and fusion cross sections are calculated using extended calculations which include the couplings to 1n and 2n transfer channels in a way which is consistent with a higher order vibrational model. 9 refs., 2 figs. (DWL)
Date: January 1, 1988
Creator: Esbensen, H.
Partner: UNT Libraries Government Documents Department

Surface response model for quasielastic scattering

Description: The description of nucleon-nucleus inelastic scattering in terms of single-scattering has been very successful at intermediate energies. Nuclear structure is the most dominant feature at low excitations and forward scattering, and the Distorted Wave Impulse Approximation (DWIA) has been the most useful technique to extract structure information. The conventional DWIA has also been applied to quasielastic scattering. However, this method is very time-consuming at large scattering angles, since many different excitations of different multipolarities contribute to the inelastic cross section. It has therefore been useful to develop an approximate treatment that contains the main physics of quasielastic scattering. In the following the author will try to establish the connection between the DWIA and the much simpler Surface Response Model. The author will give a short description of the Random Phase Approximation that is used to calculate the nuclear response, and illustrate the spin-isospin dependence of the nucleon-nucleon t-matrix interaction, which is used to generate the excitations of the target nucleus. Finally, some of the applications of the surface response model to (p,p'), (p,n) and (/sup 3/H,t) reactions are reviewed. 19 refs., 5 figs.
Date: January 1, 1987
Creator: Esbensen, H.
Partner: UNT Libraries Government Documents Department

Momentum distributions in breakup reactions

Description: Measurements of the breakup reactions: {sup 11}Be {yields} {sup 10}Be+n and{sup 8} {yields} {sup 7}Be+p are analyzed in a single-particle description. The signature of various structure properties associated with the valence nucleon axe discussed, as well as the significance of the different reaction mechanisms, namely Coulomb dissociation, stripping and nuclear induced diffraction.
Date: February 1, 1996
Creator: Esbensen, H.
Partner: UNT Libraries Government Documents Department

Correlated dipole response of neutron rich nuclei

Description: Neutron rich nuclei are expected/predicted to have a strong dipole response at low excitations. This will enhance the fragmentation cross section in reactions on a high Z target. An example is {sup 11}Li which I will discuss in detail. I will describe how one can calculate the correlated ground state and the dipole response of the valence neutrons by solving the Bethe-Goldstone equation, using an effective pairing interaction. I will also discuss how one can test the calculated low-lying dipole response. 13 refs., 2 figs.
Date: January 1, 1991
Creator: Esbensen, H.
Partner: UNT Libraries Government Documents Department

Structure and Reactions of Light Neutron Rich Nuclei

Description: Radioactive beam experiments have made it possible to study the structure of nuclei at the neutron drip line. Pair correlations play a crucial role in such nuclei and characteristic features include an extended neutron halo density and a large dipole strength near threshold. The most detailed studies have been performed for [sup 11]Li. I will present a 3-body model that explains the main features of the data obtained for this nucleus.
Date: January 1, 1993
Creator: Esbensen, H.
Partner: UNT Libraries Government Documents Department

Two-neutron transfer reactions with heavy-deformed nuclei

Description: In a recent communication we pointed out that one can combine the macroscopic model for two-particle transfer reactions on deformed nuclei with the sudden limit approximation for rotational excitation, and thereby obtain a practical method for calculating transfer reactions leading to high-spin states. As an example, we presented results for the reaction WSDy(VYNi,WNi) WDy populating the ground-state rotational band up to the spin I = 14 state. We have also tested the validity of the sudden limit for the inelastic excitation of high spin states and we have noted how the macroscopic model may be modified to allow for more microscopic nuclear structure effects in an application to diabolic pair-transfer processes. This paper describes our subsequent work in which we investigated the systematic features of pair-transfer reactions within the macroscopic model by using heavier projectiles to generate higher spins and by decomposing the cross sections according to the multipolarity of the transfer interaction. Particular attention is paid to characteristic structures in the angular distributions for the lower spin states and how they depend on the angular momentum carried by the transferred particles. 11 refs., 3 figs.
Date: January 1, 1988
Creator: Price, C.; Landowne, S. & Esbensen, H.
Partner: UNT Libraries Government Documents Department

Coulomb dissociation and momentum distributions for [sup 11]Li [yields] [sup 9]Li + n + n breakup reactions

Description: Momentum distributions for the [sup 11]Li [yields] [sup 9]Li+n+n breakup reaction, generated by Coulomb dipole excitations, axe calculated in a 3-body model for [sup 11]Li. The relative momentum distribution of the two neutrons is in good agreement with recent 3-body coincidence measurements but the momentum distribution for the [sup 9]Li recoil and the decay energy spectrum are much narrower than observed. These discrepancies may be due to higher order dynamical effects which have been ignored.
Date: January 1, 1993
Creator: Esbensen, H.
Partner: UNT Libraries Government Documents Department

Structure and reactions of light neutron rich nuclei

Description: Radioactive beam experiments have made it possible to study the structure of nuclei at the neutron drip line. Pair correlations play a crucial role in such nuclei and characteristic features include an extended neutron halo density and a large dipole strength near threshold. The most detailed studies have been performed for {sup 11}Li. I will present a 3-body model that explains the main features of the data obtained for this nucleus.
Date: April 1, 1993
Creator: Esbensen, H.
Partner: UNT Libraries Government Documents Department

Reactions of halo states: Coulomb excitations

Description: Coulomb dissociation is a relatively clean probe of the structures of one- and two-nucleon halo nuclei. This is illustrated by the breakup of {sup 11}Be, {sup 8}B and {sup 11}Li and is discussed in terms of first order perturbation theory. First-order dipole transitions usually dominate the Coulomb dissociation but quadrupole transitions are not insignificant for a proton halo (e.g. {sup 8}B). Higher-order processes can also distort the observables, such as the momentum distributions of the fragments and the excitation energy spectrum.
Date: September 1, 1997
Creator: Esbensen, H.
Partner: UNT Libraries Government Documents Department

Decay rates of spherical and deformed proton emitters

Description: Using Green's function techniques, the authors derive expressions for the width of a proton decaying state in spherical and deformed nuclei. The authors show that the proton decay widths calculated by the exact expressions of Maglione et al. are equivalent to the distorted wave expressions of Bugrov et al., and that of {angstrom} berg et al. in the spherical case.
Date: November 23, 1999
Creator: Davids, C. N. & Esbensen, H.
Partner: UNT Libraries Government Documents Department

Dynamic effects in fragmentation reactions.

Description: Fragmentation reactions offer a useful tool to study the spectroscopy of halo nuclei, but the large extent of the halo wave function makes the reaction theory more difficult. The simple reaction models based on the eikonal approximation for the nuclear interaction or first-order perturbation theory for the Coulomb interaction have systematic errors that they investigate here, comparing to the predictions of complete dynamical calculations. They find that stripping probabilities are underpredicted by the eikonal model, leading to extracted spectroscopy strengths that are two large. In contrast, the Coulomb excitation is overpredicted by the simple theory. They attribute this to a screening effect, as is well known in the Barkas effect on stopping powers. The errors decrease with beam energy as E{sub beam}{sup -1}, and are not significant at beam energies above 50 MeV/u. At lower beam energies, the effects should be taken into account when extracting quantitative spectroscopic strengths.
Date: March 26, 2002
Creator: Bertsch, G. F. & Esbensen, H.
Partner: UNT Libraries Government Documents Department

New theoretical results on the proton decay of deformed and near-spherical nuclei.

Description: We discuss new theoretical results on the decay of deformed and near-spherical nuclei. We interpret the latest experimental results on deformed odd-A proton emitters, including fine structure, and discuss the use of particle-vibration coupling to calculate the decay rates of near-spherical emitters.
Date: February 18, 2002
Creator: Davids, C. N. & Esbensen, H.
Partner: UNT Libraries Government Documents Department

Nuclear structure and sub-barrier fusion

Description: The influence of nuclear structure on heavy-ion fusion and elastic scattering, at energies near and below the Coulomb barrier, is discussed within the coupled channels formalism. The coupled channels approach provides a consistent description of the enhancement of sub-barrier fusion and the energy dependence of the effective potential for elastic scattering. This is illustrated by comparison to the data for several systems. 48 refs., 4 figs.
Date: January 1, 1990
Creator: Esbensen, H. (Michigan State Univ., East Lansing, MI (USA). Cyclotron Lab. Argonne National Lab., IL (USA))
Partner: UNT Libraries Government Documents Department

Nuclear excitation by electronic transition (NEET).

Description: We present a report on recent measurements using the Advanced Photon Source at Argonne National Laboratory to explore the phenomenon of Nuclear Excitation by Electronic Transition (NEET) in the {sup 189}Os atomic/nuclear system.
Date: April 28, 1999
Creator: Ahmad, I.; Dunford, R. W.; Esbensen, H.; Gemmell, D. S.; Kanter, E. P.; Kraessig, B. et al.
Partner: UNT Libraries Government Documents Department

The status of APS, BESSRC, and NEET.

Description: We present a brief summary of the current status of the Advanced Photon Source (APS) at Argonne National Laboratory and of the facilities at two of the APS sectors operated by the Basic Energy Sciences Synchrotrons Radiation Center (BESSRC). This is followed by a report on recent measurements at BESSRC on the phenomenon of Nuclear Excitation by Electronic Transition (NEET).
Date: March 10, 1999
Creator: Ahmad, I.; Dunford, R. W.; Esbensen, H.; Gemmell, D. S.; Kanter, E. P.; Kraessig, B. et al.
Partner: UNT Libraries Government Documents Department

Comment on Measurement of the Z sub 1 sup 3 contribution to the stopping power using MeV protons and antiprotons, the Barkas effect''

Description: In a recent Letter, Andersen et al. reported measured energy losses of 0.5--3.0 MeV protons and antiprotons in silicon and extracted the Z{sub 1}{sup 3} (or Barkas) correction to the stopping power. They compared their results to calculations that are valid for distant collisions and are based on a perturbation expansion for the excitation of a classical harmonic oscillator. The authors mentioned that there has been a long-standing discussion about the contribution from close collisions to the Z{sub 1}{sup 3} correction, but that no agreement had been reached in view of lacking quantitative calculations. In this Comment we report on the results of recent theoretical evaluations of the Z{sub 1}{sup 3} correction in two different models, a spherical harmonic oscillator and a static electron gas. The calculations are quantal and include the effect of both close and distant collisions.
Date: January 1, 1991
Creator: Mikkelsen, H.H. (Odense Univ. (Denmark)); Esbensen, H. (Argonne National Lab., IL (USA)) & Sigmund, P. (Argonne National Lab., IL (USA) Odense Univ. (Denmark))
Partner: UNT Libraries Government Documents Department

Sub-barrier fusion and near-barrier quasi-elastic scattering

Description: Elastic scattering of {sup 32}S on {sup 58,64}Ni and fusion of {sup 32}S+{sup 58,64}Ni and {sup 34}S+{sup 64}Ni have been measured at energies near the Coulomb barrier. Our results differ in several important respects from previous measurements on these systems. Coupled-channels calculations which explicitly allow for inelastic excitation and single-nucleon transfer reproduce the main features of the new data. Near-barrier elastic scattering of {sup 48}Ca on {sup 40}Ca has also been measured. These data provide evidence for the effect of strong coupling to positive Q-value channels other than single-nucleon transfer. 18 refs., 3 figs.
Date: January 1, 1990
Creator: Kolata, J.J.; Tighe, R.J. (Notre Dame Univ., IN (USA). Dept. of Physics); Fricke, S.H.; Esbensen, H. & Landowne, S. (Argonne National Lab., IL (USA))
Partner: UNT Libraries Government Documents Department