567 research outputs found

### Nuclear structure with accurate chiral perturbation theory nucleon-nucleon potential: Application to 6Li and 10B

We calculate properties of A=6 system using the accurate charge-dependent
nucleon-nucleon (NN) potential at fourth order of chiral perturbation theory.
By application of the ab initio no-core shell model (NCSM) and a variational
calculation in the harmonic oscillator basis with basis size up to 16 hbarOmega
we obtain the 6Li binding energy of 28.5(5) MeV and a converged excitation
spectrum. Also, we calculate properties of 10B using the same NN potential in a
basis space of up to 8 hbarOmega. Our results are consistent with results
obtained by standard accurate NN potentials and demonstrate a deficiency of
Hamiltonians consisting of only two-body terms. At this order of chiral
perturbation theory three-body terms appear. It is expected that inclusion of
such terms in the Hamiltonian will improve agreement with experiment.Comment: 9 pages, 14 figure

### Proton radii of 4,6,8He isotopes from high-precision nucleon-nucleon interactions

Recently, precision laser spectroscopy on 6He atoms determined accurately the
isotope shift between 4He and 6He and, consequently, the charge radius of 6He.
A similar experiment for 8He is under way. We have performed large-scale ab
initio calculations for 4,6,8He isotopes using high-precision nucleon-nucleon
(NN) interactions within the no-core shell model (NCSM) approach. With the
CD-Bonn 2000 NN potential we found point-proton root-mean-square (rms) radii of
4He and 6He 1.45(1) fm and 1.89(4), respectively, in agreement with experiment
and predict the 8He point proton rms radius to be 1.88(6) fm. At the same time,
our calculations show that the recently developed nonlocal INOY NN potential
gives binding energies closer to experiment, but underestimates the charge
radii.Comment: 5 pages, 9 figure

### Large basis ab initio shell model investigation of 9-Be and 11-Be

We are presenting the first ab initio structure investigation of the loosely
bound 11-Be nucleus, together with a study of the lighter isotope 9-Be. The
nuclear structure of these isotopes is particularly interesting due to the
appearance of a parity-inverted ground state in 11-Be. Our study is performed
in the framework of the ab initio no-core shell model. Results obtained using
four different, high-precision two-nucleon interactions, in model spaces up to
9\hbar\Omega, are shown. For both nuclei, and all potentials, we reach
convergence in the level ordering of positive- and negative-parity spectra
separately. Concerning their relative position, the positive-parity states are
always too high in excitation energy, but a fast drop with respect to the
negative-parity spectrum is observed when the model space is increased. This
behavior is most dramatic for 11-Be. In the largest model space we were able to
reach, the 1/2+ level has dropped down to become either the first or the second
excited state, depending on which interaction we use. We also observe a
contrasting behavior in the convergence patterns for different two-nucleon
potentials, and argue that a three-nucleon interaction is needed to explain the
parity inversion. Furthermore, large-basis calculations of 13-C and 11-B are
performed. This allows us to study the systematics of the position of the first
unnatural-parity state in the N=7 isotone and the A=11 isobar. The 11-B run in
the 9\hbar\Omega model space involves a matrix with dimension exceeding 1.1 x
10^9, and is our largest calculation so far. We present results on binding
energies, excitation spectra, level configurations, radii, electromagnetic
observables, and 10-Be+n overlap functions.Comment: 17 pages, 12 figures To be published in Phys. Rev. C Resubmitted
version. Minor change

### A Time Dependent Multi-Determinant approach to nuclear dynamics

We study a multi-determinant approach to the time evolution of the nuclear
wave functions (TDMD). We employ the Dirac variational principle and use as
anzatz for the nuclear wave-function a linear combination of Slater
determinants and derive the equations of motion. We demonstrate explicitly that
the norm of the wave function and the energy are conserved during the time
evolution. This approach is a direct generalization of the time dependent
Hartree-Fock method. We apply this approach to a case study of ${}^6Li$ using
the N3LO interaction renormalized to 4 major harmonic oscillator shells. We
solve the TDMD equations of motion using Krylov subspace methods of Lanczos
type. We discuss as an application the isoscalar monopole strength function.Comment: 38 pages, additional calculations included. Accepted for publication,
Int. J. of Mod. Phys.

### Shell model study of the isobaric chains A=50, A=51 and A=52

Shell model calculations in the full pf-shell are carried out for the A=50,
51 and 52 isobars. The most frequently used effective interactions for the
pf-shell, KB3 and FPD6 are revisited and their behaviour at the N=28 and Z=28
closures examined. Cures to their -relatively minor- defaults are proposed, and
a new mass dependent version called KB3G is released. Energy spectra,
electromagnetic transitions and moments as well as beta decay properties are
computed and compared with the experiment and with the results of the earlier
interactions. A high quality description is achieved. Other miscellaneous
topics are addressed; the Coulomb energy differences of the yrast states of the
mirror pair 51Mn-51Fe and the systematics of the magnetic moments of the N=28
isotones.Comment: 45 pages, 34 figures, Latex. Submitted for publicatio

### Shell Model Description of Isotope Shifts in Calcium

Isotope shifts in the nuclear charge radius of even and odd calcium isotopes
are calculated within the nuclear shell model. The model space includes all
configurations of nucleons in the $2s, 1d_{3/2}, 1f_{7/2}, {\rm and} ~2p_{3/2}$
orbits. The shell model describes well the energies of the intruder states in
Sc and Ca, as well as the energies of the low-lying $2^+$ and $3^-$ states in
the even Ca isotopes. The characteristic features of the isotope shifts, the
parabolic dependence on $A$ and the prominent odd-even staggering, are well
reproduced by the model. These features are related to the partial breakdown of
the $Z = 20$ shell closure caused by promotion, due to the neutron-proton
interaction, of the $ds$ shell protons into the $fp$ shell.Comment: 4 pages, 4 figures include

### Canonical form of Hamiltonian matrices

On the basis of shell model simulations, it is conjectured that the Lanczos
construction at fixed quantum numbers defines---within fluctuations and
behaviour very near the origin---smooth canonical matrices whose forms depend
on the rank of the Hamiltonian, dimensionality of the vector space, and second
and third moments. A framework emerges that amounts to a general Anderson model
capable of dealing with ground state properties and strength functions. The
smooth forms imply binomial level densities. A simplified approach to canonical
thermodynamics is proposed.Comment: 4 pages 6 figure

### Quantum Chaos in A=46--50 Atomic Nuclei

The spectral statistics of low--lying states of several $fp$ shell nuclei are
studied with realistic shell--model calculations. For Ca isotopes, we find
significant deviations from the predictions of the random--matrix theory which
suggest that some spherical nuclei are not as chaotic in nature as the
conventional view assumes.Comment: 12 pages, LaTex, 2 figures available upon request, to be published in
Physics Letters

### Shape Coexistence in 78 Ni and the new Island of Inversion

Large Scale Shell Model calculations (SM-CI) predict that the region of
deformation which comprises the heaviest Chromium and Iron isotopes at and
beyond N=40 will merge with a new one at N=50 in an astonishing parallel to the
N=20 and N=28 case in the Neon and Magnesium isotopes. We propose a valence
space including the full pf-shell for the protons and the full sdg shell for
the neutrons; which represents a comeback of the the harmonic oscillator shells
in the very neutron rich regime. The onset of deformation is understood in the
framework of the algebraic SU3-like structures linked to quadrupole dominance.
Our calculations preserve the doubly magic nature of the ground state of 78 Ni,
which, however, exhibits a well deformed prolate band at low excitation energy,
providing a striking example of shape coexistence far from stability

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