527 research outputs found
Exotic nuclei far from the stability line
The recent availability of radioactive beams has opened up a new era in
nuclear physics. The interactions and structure of exotic nuclei close to the
drip lines have been studied extensively world wide, and it has been revealed
that unstable nuclei, having weakly bound nucleons, exhibit characteristic
features such as a halo structure and a soft dipole excitation. We here review
the developments of the physics of unstable nuclei in the past few decades. The
topics discussed in this Chapter include the halo and skin structures, the
Coulomb breakup, the dineutron correlation, the pair transfer reactions, the
two-nucleon radioactivity, the appearance of new magic numbers, and the pygmy
dipole resonances.Comment: 43 pages, 30 eps figures. chapter in "100 years of subatomic
physics", edited by E.M. Henley and S. Elli
Microscopic multicluster description of neutron-halo nuclei with a stochastic variational method
To test a multicluster approach for halo nuclei, we give a unified
description for the ground states of He and He in a model comprising an
cluster and single-neutron clusters. The intercluster wave function is
taken a superposition of terms belonging to different arrangements, each
defined by a set of Jacobi coordinates. Each term is then a superposition of
products of gaussian functions of the individual Jacobi coordinates with
different widths, projected to angular momenta or 1. To avoid excessively
large dimensions and ``overcompleteness", stochastic methods were tested for
selecting the gaussians spanning the basis. For He, we were able to
calculate ground-state energies that are virtully exact within the subspace
defined by the arrangements and values, and we found that preselected
random sets of bases (with or without simulated annealing) yield excellent
numerical convergence to this ``exact" value with thoroughly truncated bases.
For He good energy convergence was achieved in a state space comprising
three arrangements with all , and there are indications showing that the
contributions of other subspaces are likely to be small. The He and He
energies are reproduced by the same effective force very well, and the matter
radii obtained are similar to those of other sophisticated calculations.Comment: Latex , 8 figures available on request, ATOMKI-4-1993-
Tensor-optimized shell model for the Li isotopes with a bare nucleon-nucleon interaction
We study the Li isotopes systematically in terms of the tensor-optimized
shell model (TOSM) by using a bare nucleon-nucleon interaction as the AV8'
interaction. The short-range correlation is treated in the unitary correlation
operator method (UCOM). Using the TOSM+UCOM approach, we investigate the role
of the tensor force on each spectrum of the Li isotopes. It is found that the
tensor force produces quite a characteristic effect on various states in each
spectrum and those spectra are affected considerably by the tensor force. The
energy difference between the spin-orbit partner, the p1/2 and p3/2 orbits of
the last neutron, in 5Li is caused by opposite roles of the tensor correlation.
In 6Li, the spin-triplet state in the LS coupling configuration is favored
energetically by the tensor force in comparison with jj coupling shell model
states. In 7,8,9Li, the low-lying states containing extra neutrons in the p3/2
orbit are favored energetically due to the large tensor contribution to allow
the excitation from the 0s orbit to the p1/2 orbit by the tensor force. Those
three nuclei show the jj coupling character in their ground states which is
different from 6Li.Comment: 12 pages, 6 figures. arXiv admin note: text overlap with
arXiv:1108.393
Structure Functions of Unstable Lithium Isotopes
We study both the spin-average and spin-dependent structure functions of the
lithium isotopes, Li, which could be measured at RIKEN and other
nuclear facilities in the future. It is found that the light-cone momentum
distribution of the valence neutron in the halo of Li is very sharp and
symmetric around y = 1, because of the weak binding. The EMC ratios for Li
isotopes are then calculated. We study the possibility of extracting the
neutron structure function from data for the nuclear structure functions of the
Li isotopes. Next we calculate the spin-dependent structure functions of
Li isotopes, which have spin of 3/2. The effect of the nuclear
binding and Fermi motion on the multipole spin structure function,
, is about 10% in the region x < 0.7, but it becomes quite
important at large x. The spin structure function of is also
investigated. Finally, we discuss the modification of the Gottfried and Bjorken
integrals in a nuclear medium and point out several candidates for a pair of
mirror nuclei to study the flavor-nonsinglet quark distributions in nuclei.Comment: 23 pages + 7 tables + 15 figure
Hyperfine Anomaly of Be Isotopes and Anomalous Large Anomaly in Be
A new result of investigations of the hyperfine structure (hfs) anomaly in Be
isotopes is presented. The hfs constant for Be is obtained by using the
core plus neutron type wave function: . A large hfs anomaly of Be is found, which is mainly due
to a large radius of the halo single particle state.Comment: 14 pages, Late
Pairing anti-halo effect
We discuss pairing correlations in weakly bound neutron rich nuclei, by using
the coordinate-space Hartree-Fock-Bogolyubov approach which allows to take
properly into account the coupling to particle continuum. We show that the
additional pairing binding energy acts against a development of an infinite rms
radius, even in situations when an l=0 single-particle orbital becomes unbound.Comment: 10 RevTeX pages, 3 EPS figure
Microscopic description of light unstable nuclei with the stochastic variational method
The structure of the light proton and neutron rich nuclei is studied in a
microscopic multicluster model using the stochastic variational method. This
approach enables us to describe the weakly bound nature of these nuclei in a
consistent way. Applications for various nuclei Li, Be, B,
C, Be, B presented. The paper discusses the relation of
this model to other models as well as the possible extension for p and sd shell
nuclei.Comment: 11 pages, latex, no figures
Modified Bethe-Weizsacker mass formula with isotonic shift and new driplines
Nuclear masses are calculated using the modified Bethe-Weizsacker mass
formula in which the isotonic shifts have been incorporated. The results are
compared with the improved liquid drop model with isotonic shift. Mass excesses
predicted by this method compares well with the microscopic-macroscopic model
while being much more simple. The neutron and proton drip lines have been
predicted using this modified Bethe-Weizsacker mass formula with isotonic
shifts.Comment: 9 pages including 2 figure
Application of Absorbing Boundary Condition to Nuclear Breakup Reactions
Absorbing boundary condition approach to nuclear breakup reactions is
investigated. A key ingredient of the method is an absorbing potential outside
the physical area, which simulates the outgoing boundary condition for
scattered waves. After discretizing the radial variables, the problem results
in a linear algebraic equation with a sparse coefficient matrix, to which
efficient iterative methods can be applicable. No virtual state such as
discretized continuum channel needs to be introduced in the method. Basic
aspects of the method are discussed by considering a nuclear two-body
scattering problem described with an optical potential. We then apply the
method to the breakup reactions of deuterons described in a three-body direct
reaction model. Results employing the absorbing boundary condition are found to
accurately coincide with those of the existing method which utilizes
discretized continuum channels.Comment: 21 pages, 5 figures, RevTeX
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