69 research outputs found
Quadratic momentum dependence in the nucleon-nucleon interaction
We investigate different choices for the quadratic momentum dependence
required in nucleon-nucleon potentials to fit phase shifts in high
partial-waves. In the Argonne v18 potential L**2 and (L.S)**2 operators are
used to represent this dependence. The v18 potential is simple to use in
many-body calculations since it has no quadratic momentum-dependent terms in
S-waves. However, p**2 rather than L**2 dependence occurs naturally in
meson-exchange models of nuclear forces. We construct an alternate version of
the Argonne potential, designated Argonne v18pq, in which the L**2 and (L.S)**2
operators are replaced by p**2 and Qij operators, respectively. The quadratic
momentum-dependent terms are smaller in the v18pq than in the v18 interaction.
Results for the ground state binding energies of 3H, 3He, and 4He, obtained
with the variational Monte Carlo method, are presented for both the models with
and without three-nucleon interactions. We find that the nuclear wave functions
obtained with the v18pq are slightly larger than those with v18 at
interparticle distances < 1 fm. The two models provide essentially the same
binding in the light nuclei, although the v18pq gains less attraction when a
fixed three-nucleon potential is added.Comment: v.2 important corrections in tables and minor revisions in text;
reference for web-posted subroutine adde
Nuclear Polarizabilities and Logarithmic Sum Rules
The electric polarizability and logarithmic mean-excitation energy are
calculated for the deuteron using techniques introduced in atomic physics.
These results are then used to improve limits on the atomic-deuterium frequency
shift due to nuclear polarization in the unretarded dipole limit, as well as
confirming previous results.Comment: 7 pages, latex -- To appear in Phys. Rev. C -
NN Scattering: Chiral Predictions for Asymptotic Observables
We assume that the nuclear potential for distances larger than 2.5 fm is
given just by the exchanges of one and two pions and, for the latter, we adopt
a model based on chiral symmetry and subthreshold pion-nucleon amplitudes,
which contains no free parameters. The predictions produced by this model for
nucleon-nucleon observables are calculated and shown to agree well with both
experiment and those due to phenomenological potentials.Comment: 16 pages, 12 PS figures included, to appear in Physical Review
Peripheral N Scattering: A Tool For Identifying The Two Pion Exchange Component Of The NN Potential
We study elastic N scattering and produce a quantitative correlation
between the range of the effective potential and the energy of the system. This
allows the identification of the waves and energies for which the scattering
may be said to be peripheral. We then show that the corresponding phase shifts
are sensitive to the tail of the NN potential, which is due to the exchange of
two pions. However, the present uncertainties in the experimental phase shifts
prevent the use of N scattering to discriminate the existing models
for the NN interaction.Comment: 19 pages, 6 PostScript figures, RevTeX, to be appear in Phys. Rev.
Resonances in the three-neutron system
A study of 3-body resonances has been performed in the framework of
configuration space Faddeev equations. The importance of keeping a sufficient
number of terms in the asymptotic expansion of the resonance wave function is
pointed out. We investigated three neutrons interacting in selected force
components taken from realistic nn forces.Comment: 38 pages, 11 tables, 4 figure
Effective density dependent pairing forces in the T=1 and T=0 channels
Effective density dependent pairing forces of zero range are adjusted on gap
values in T=0,1 channels calculated with the Paris force in symmetric nuclear
matter. General discussions on the pairing force are presented. In conjunction
with the effective k-mass the nuclear pairing force seems to need very little
renormalization in the T=1 channel. The situation in the T=0 channel is also
discussed.Comment: 6 pages, 8 figures, to be published in PR
Higher-Order Nuclear-Polarizability Corrections in Atomic Hydrogen
Nuclear-polarizability corrections that go beyond unretarded-dipole
approximation are calculated analytically for hydrogenic (atomic) S-states.
These retardation corrections are evaluated numerically for deuterium and
contribute -0.68 kHz, for a total polarization correction of 18.58(7) kHz. Our
results are in agreement with one previous numerical calculation, and the
retardation corrections completely account for the difference between two
previous calculations. The uncertainty in the deuterium polarizability
correction is substantially reduced. At the level of 0.01 kHz for deuterium,
only three primary nuclear observables contribute: the electric polarizability,
, the paramagnetic susceptibility, , and the third Zemach
moment, . Cartesian multipole decomposition of the virtual
Compton amplitude and its concomitant gauge sum rules are used in the analysis.Comment: 26 pages, latex, 1 figure -- Submitted to Phys. Rev. C -- epsfig.sty
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Nuclear Sizes and the Isotope Shift
Darwin-Foldy nuclear-size corrections in electronic atoms and nuclear radii
are discussed from the nuclear-physics perspective. Interpretation of precise
isotope-shift measurements is formalism dependent, and care must be exercised
in interpreting these results and those obtained from relativistic electron
scattering from nuclei. We strongly advocate that the entire nuclear-charge
operator be used in calculating nuclear-size corrections in atoms, rather than
relegating portions of it to the non-radiative recoil corrections. A
preliminary examination of the intrinsic deuteron radius obtained from
isotope-shift measurements suggests the presence of small meson-exchange
currents (exotic binding contributions of relativistic order) in the nuclear
charge operator, which contribute approximately 1/2%.Comment: 17 pages, latex, 1 figure -- Submitted to Phys. Rev. A -- epsfig.sty
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Two-Pion Exchange Nucleon-Nucleon Potential: Model Independent Features
A chiral pion-nucleon amplitude supplemented by the HJS subthreshold
coefficients is used to calculate the the long range part of the two-pion
exchange nucleon-nucleon potential. In our expressions the HJS coefficients
factor out, allowing a clear identification of the origin of the various
contributions. A discussion of the configuration space behaviour of the loop
integrals that determine the potential is presented, with emphasis on
cancellations associated with chiral symmetry. The profile function for the
scalar-isoscalar component of the potential is produced and shown to disagree
with those of several semi-phenomenological potentials.Comment: 16 pages, 9 embedded figures, Latex 2.09, Revtex.sty, epsf.st
Elements Discrimination in the Study of Super-Heavy Elements using an Ionization Chamber
Dedicated ionization chamber was built and installed to measure the energy
loss of very heavy nuclei at 2.7 MeV/u produced in fusion reactions in inverse
kinematics (beam of 208Pb). After going through the ionization chamber,
products of reactions on 12C, 18O targets are implanted in a Si detector. Their
identification through their alpha decay chain is ambiguous when their
half-life is short. After calibration with Pb and Th nuclei, the ionization
chamber signal allowed us to resolve these ambiguities. In the search for rare
super-heavy nuclei produced in fusion reactions in inverse or symmetric
kinematics, such a chamber will provide direct information on the nuclear
charge of each implanted nucleus.Comment: submitted to NIMA, 10 pages+4 figures, Latex, uses elsart.cls and
grahpic
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