144 research outputs found
Two-proton radioactivity and three-body decay. III. Integral formulae for decay widths in a simplified semianalytical approach
Three-body decays of resonant states are studied using integral formulae for
decay widths. Theoretical approach with a simplified Hamiltonian allows
semianalytical treatment of the problem. The model is applied to decays of the
first excited state of Ne and the ground state of
Fe. The convergence of three-body hyperspherical model calculations to
the exact result for widths and energy distributions are studied. The
theoretical results for Ne and Fe decays are updated and
uncertainties of the derived values are discussed in detail. Correlations for
the decay of Ne state are also studied.Comment: 19 pages, 20 figure
Halo Excitation of He in Inelastic and Charge-Exchange Reactions
Four-body distorted wave theory appropriate for nucleon-nucleus reactions
leading to 3-body continuum excitations of two-neutron Borromean halo nuclei is
developed. The peculiarities of the halo bound state and 3-body continuum are
fully taken into account by using the method of hyperspherical harmonics. The
procedure is applied for A=6 test-bench nuclei; thus we report detailed studies
of inclusive cross sections for inelastic He(p,p')He and
charge-exchange Li(n,p)He reactions at nucleon energy 50 MeV. The
theoretical low-energy spectra exhibit two resonance-like structures. The first
(narrow) is the excitation of the well-known three-body resonance. The
second (broad) bump is a composition of overlapping soft modes of
multipolarities whose relative weights depend on
transferred momentum and reaction type. Inelastic scattering is the most
selective tool for studying the soft dipole excitation mode.Comment: Submitted to Phys. Rev. C., 11 figures using eps
Algebraic Model for scattering of three-s-cluster systems. II. Resonances in the three-cluster continuum of 6He and 6Be
The resonance states embedded in the three-cluster continuum of 6He and 6Be
are obtained in the Algebraic Version of the Resonating Group Method. The model
accounts for a correct treatment of the Pauli principle. It also provides the
correct three-cluster continuum boundary conditions by using a Hyperspherical
Harmonics basis. The model reproduces the observed resonances well and achieves
good agreement with other models. A better understanding for the process of
formation and decay of the resonance states in six-nucleon systems is obtained.Comment: 8 pages, 10 postscript figures, submitted to Phys. Rev.
Three-body continuum energy correlations in Borromean halo nuclei. III. Short-range external fields
Excitations in the Halo Nucleus He-6 Following The Li-7(gamma,p)He-6 Reaction
A broad excited state was observed in 6-He with energy E_x = 5 +/- 1 MeV and
width Gamma = 3 +/- 1 MeV, following the reaction Li-7(gamma,p)He-6. The state
is consistent with a number of broad resonances predicted by recent cluster
model calculations. The well-established reaction mechanism, combined with a
simple and transparent analysis procedure confers considerable validity to this
observation.Comment: 3 pages of LaTeX, 3 figures in PostScript, approved for publication
in Phys. Rev. C, August, 200
Comment on ``Large-space shell-model calculations for light nuclei''
In a recent publication Zheng, Vary, and Barrett reproduced the negative
quadrupole moment of Li-6 and the low-lying positive-parity states of He-5 by
using a no-core shell model. In this Comment we question the meaning of these
results by pointing out that the model used is inadequate for the reproduction
of these properties.Comment: Latex with Revtex, 1 postscript figure in separate fil
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Transition energy correlations in the three-body continuum of Borromean halo nuclei
Energy correlations in transitions from the bound state to the three-body continuum of Borromean halo nuclei are considered. A core+n+n three-body cluster model which reproduces experimentally known properties of {sup 6}He and {sup 11}Li has been used to study low-lying resonances and soft modes. The analysis of the correlated responses in {sup 6}He shows that in the case of the narrow three-body 2{sub 1}{sup +} resonance the transition energy correlations are the same as in the intrinsic correlated structure in 3 {yields} 3 scattering. They differ significantly for wide 2{sub 2}{sup +}, 1{sub 1}{sup +} resonances, and also for the soft dipole and monopole modes, where, due to the transition operators, the intertwining of the ground state and the three-body continuum plays a significant role
Peculiar properties of the cluster-cluster interaction induced by the Pauli exclusion principle
Role of the Pauli principle in the formation of both the discrete spectrum
and multi-channel states of the binary nuclear systems composed of clusters is
studied in the Algebraic Version of the resonating-group method. Solutions of
the Hill-Wheeler equations in the discrete representation of a complete basis
of the Pauli-allowed states are discussed for 4He+n, 3H+3H, and 4He+4He binary
systems. An exact treatment of the antisymmetrization effects are shown to
result in either an effective repulsion of the clusters, or their effective
attraction. It also yields a change in the intensity of the centrifugal
potential. Both factors significantly affect the scattering phase behavior.
Special attention is paid to the multi-channel cluster structure 6He+6He as
well as to the difficulties arising in the case when the two clustering
configurations, 6He+6He and 4He+8He, are taken into account simultaneously. In
the latter case the Pauli principle, even in the absence of a potential energy
of the cluster-cluster interaction, leads to the inelastic processes and
secures an existence of both the bound state and resonance in the 12Be compound
nucleus.Comment: 17 pages, 14 figures, 1 table; submitted to Phys.Rev.C Keywords:
light neutron-rich nuclei, cluster model
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