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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

Ternary particles with extreme N/Z ratios from neutron-induced fission

Description: The existing ternary fission models can well reproduce the yields of the most abundant light charged particles. However, these models tend to significantly overestimate the yields of ternary particles with an extreme N/Z ratio: {sup 3}He, {sup 11}Li, {sup 14}Be, etc. The experimental yields of these isotopes were investigated with the recoil separator LOHENGRIN down to a level of 10{sup {minus}10} per fission. Results from the fissioning systems {sup 233}U (n{sub th}, f), {sup 235}U(n{sub th},f), {sup 239}Pu(n{sub th},f) {sup 241}Pu(n{sub th},f) and {sup 245}Cm(n{sub th},f) are presented and the implications for the ternary fission models are discussed.
Date: May 16, 2000
Creator: Koster, U.; Faust, H.; Friedrichs, T.; Oberstedt, S.; Fioni, G.; Grob, M. et al.
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: March 1, 1993
Creator: Esbensen, Henning
Partner: UNT Libraries Government Documents Department

SU(3) symmetries in exotic neutron-rich nuclei

Description: We examine the structure of the exotic neutron-rich nucleus {sup 11}Li with an emphasis on understanding the origin of the soft E1 resonance and the neuron halo. The similarities and differences between shell model and di-neutron cluster model descriptions of the system are displayed using the Hecht expansion techniques. We find that the ground state {sup 11}Li as described in large shell model calculations is well approximated by the di-neutron cluster state. In contrast to the ground state, the soft E1 model of {sup 11}Li appears to have a more complicated structure and the E1 strength of this resonance is very sensitive to cancellations between p{yields}s and p{yields}d contributions to the dipole matrix elements. 12 refs., 6 figs., 3 tabs.
Date: December 31, 1991
Creator: Hayes, A. C.
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

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

The sup 11 Li neutron halo radius from pion double charge exchange

Description: We have analzed the pion double charge exchange data for the direct population of the ground state of {sup 11}Li by the {sup 11}B({pi}{sup {minus}}, {pi}{sup +}){sup 11}Li reaction and find that the measured cross section determines the rms radius of the last two neutrons in {sup 11}Li to be 5.1{sub {minus} 0.8}{sup +0.6} fm. It is shown that the pion cross-section falls off as the sixth power of the assumed neutron halo radius, so that a radius greater than about 6 fm is ruled out. Indeed, pion double charge is found to act as an unusually sensitive probe of the properties of this exotic neutron rich nucleus. 9 refs., 2 figs.
Date: January 1, 1991
Creator: Hayes, A.C.
Partner: UNT Libraries Government Documents Department

SU(3) symmetries in exotic neutron-rich nuclei

Description: We examine the structure of the exotic neutron-rich nucleus {sup 11}Li with an emphasis on understanding the origin of the soft E1 resonance and the neuron halo. The similarities and differences between shell model and di-neutron cluster model descriptions of the system are displayed using the Hecht expansion techniques. We find that the ground state {sup 11}Li as described in large shell model calculations is well approximated by the di-neutron cluster state. In contrast to the ground state, the soft E1 model of {sup 11}Li appears to have a more complicated structure and the E1 strength of this resonance is very sensitive to cancellations between p{yields}s and p{yields}d contributions to the dipole matrix elements. 12 refs., 6 figs., 3 tabs.
Date: January 1, 1991
Creator: Hayes, A.C.
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

The sup 11 Li neutron halo radius from pion double charge exchange

Description: We have analyzed the pion double charge exchange data for the direct population of the ground state of {sup 11}Li by the {sup 11}B({pi}{sup minus},{pi}{sup +}){sup 11}Li reaction and find that the measured cross section determines the rms radius of the last two neutrons in {sup 11}Li to be 5.1{sub {minus}0.8}{sup +0.6} fm. 8 refs., 2 figs.
Date: January 1, 1991
Creator: Gibbs, W.R. & Hayes, A.C.
Partner: UNT Libraries Government Documents Department

Direct mass measurements of light neutron-rich nuclei using fast recoil spectrometers

Description: Extensive new mass measurement capabilities have evolved with the development of recoil spectrometers. In the Z = 3 to 9 neutron-rich region alone, 12 neutron-rich nuclei have been determined for the first time by the fast-recoil direct mass measurement method. A recent experiment using the TOFI spectrometer illustrates this technique. A systematic investigation of nuclei that lie along or near the neutron-drip line has provided a valuable first glimpse into the nuclear structure of such nuclei. No evidence for a large single-particle energy gap at N = 14 is observed; however, a change in the two-neutron separation model calculations, and is interpreted in terms of the smaller 1s/sub 1/2/ - 1s/sub 1/2/ interaction compared to that of the 0d/sub 5/2/ - 0d/sub 5/2/ neutron-neutron interaction. 18 refs., 7 figs., 1 tab.
Date: January 1, 1987
Creator: Vieira, D.J. & Wouters, J.M.
Partner: UNT Libraries Government Documents Department