23,793 research outputs found
Cold neutrons trapped in external fields
The properties of inhomogeneous neutron matter are crucial to the physics of
neutron-rich nuclei and the crust of neutron stars. Advances in computational
techniques now allow us to accurately determine the binding energies and
densities of many neutrons interacting via realistic microscopic interactions
and confined in external fields. We perform calculations for different external
fields and across several shells to place important constraints on
inhomogeneous neutron matter, and hence the large isospin limit of the nuclear
energy density functionals that are used to predict properties of heavy nuclei
and neutron star crusts. We find important differences between microscopic
calculations and current density functionals; in particular the isovector
gradient terms are significantly more repulsive than in traditional models, and
the spin-orbit and pairing forces are comparatively weaker.Comment: 5 pages, 4 figures, final version. Additional material reference
added in the published versio
Electron densities and temperatures in the f-region from backscatter measurements at arecibo
Diurnal variation in electron densities and temperatures in F region from backscatter measurements over Puerto Ric
Quantum Monte Carlo study of inhomogeneous neutron matter
We present an ab-initio study of neutron drops. We use Quantum Monte Carlo
techniques to calculate the energy up to 54 neutrons in different external
potentials, and we compare the results with Skyrme forces. We also calculate
the rms radii and radial densities, and we find that a re-adjustment of the
gradient term in Skyrme is needed in order to reproduce the properties of these
systems given by the ab-initio calculation. By using the ab-initio results for
neutron drops for close- and open-shell configurations, we suggest how to
improve Skyrme forces when dealing with systems with large isospin-asymmetries
like neutron-rich nuclei.Comment: 8 pages, 6 figures, talk given at Horizons on Innovative Theories,
Experiments, and Supercomputing in Nuclear Physics 2012, (HITES2012), New
Orleans, Louisiana, June 4-7, 2012; to appear in Journal of Physics:
Conference Series (JPCS
Leading-Log Effects in the Resonance Electroweak Form Factors
We study log corrections to inelastic scattering at high Bjorken x for Q^2
from 1 to 21 GeV^2. At issue is the presence of log corrections, which can be
absent if high x scattering has damped gluon radiation. We find logarithmic
correction of the scaling curve extrapolated to low Q^2 improves the duality
between it and the resonance plus background data in the Delta region,
indicating log corrections exist in the data. However, at W > 2 GeV and high x,
the data shows a (1-x)^3 form. Log corrections in one situation but not in
another can be reconciled by a W- or Q^2- dependent higher twist correction.Comment: 13 pages, report nos. RPI-94-N90 and WM-94-106, revtex, two figures
(available by fax or post
Quantum Monte Carlo Calculations of Nuclei
The energies of , , and ground states, the
and scattering states of , the
ground states of , , and and the and
excited states of have been accurately calculated with the Green's
function Monte Carlo method using realistic models of two- and three-nucleon
interactions. The splitting of the isospin and
isospin , multiplets is also studied. The observed
energies and radii are generally well reproduced, however, some definite
differences between theory and experiment can be identified.Comment: 12 pages, 1 figur
Quantum Monte Carlo calculations of excited states in A = 6--8 nuclei
A variational Monte Carlo method is used to generate sets of orthogonal trial
functions, Psi_T(J^pi,T), for given quantum numbers in various light p-shell
nuclei. These Psi_T are then used as input to Green's function Monte Carlo
calculations of first, second, and higher excited (J^pi,T) states. Realistic
two- and three-nucleon interactions are used. We find that if the physical
excited state is reasonably narrow, the GFMC energy converges to a stable
result. With the combined Argonne v_18 two-nucleon and Illinois-2 three-nucleon
interactions, the results for many second and higher states in A = 6--8 nuclei
are close to the experimental values.Comment: Revised version with minor changes as accepted by Phys. Rev. C. 11
page
Tensor Forces and the Ground-State Structure of Nuclei
Two-nucleon momentum distributions are calculated for the ground states of
nuclei with mass number , using variational Monte Carlo wave functions
derived from a realistic Hamiltonian with two- and three-nucleon potentials.
The momentum distribution of pairs is found to be much larger than that of
pairs for values of the relative momentum in the range (300--600) MeV/c
and vanishing total momentum. This order of magnitude difference is seen in all
nuclei considered and has a universal character originating from the tensor
components present in any realistic nucleon-nucleon potential. The correlations
induced by the tensor force strongly influence the structure of pairs,
which are predominantly in deuteron-like states, while they are ineffective for
pairs, which are mostly in S states. These features should be
easily observable in two-nucleon knock-out processes, such as and .Comment: 4 pages including 3 figure
Dependence of two-nucleon momentum densities on total pair momentum
Two-nucleon momentum distributions are calculated for the ground states of
3He and 4He as a function of the nucleons' relative and total momenta. We use
variational Monte Carlo wave functions derived from a realistic Hamiltonian
with two- and three-nucleon potentials. The momentum distribution of pp pairs
is found to be much smaller than that of pn pairs for values of the relative
momentum in the range (300--500) MeV/c and vanishing total momentum. However,
as the total momentum increases to 400 MeV/c, the ratio of pp to pn pairs in
this relative momentum range grows and approaches the limit 1/2 for 3He and 1/4
for 4He, corresponding to the ratio of pp to pn pairs in these nuclei. This
behavior should be easily observable in two-nucleon knock-out processes, such
as A(e,e'pN).Comment: 3 pages, 3 figure
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