11,305 research outputs found
On the measurement of B(E2, 0+ -> 2+) using intermediate-energy Coulomb excitation
Coulomb excitation is a standard method used to extract quadrupole excitation
strengths of even-even nuclei. In typical analyses the reaction is assumed to
be one-step, Coulomb only, and is treated within a semi-classical model. In
this work, fully-quantal coupled-channel calculations are performed for three
test cases in order to determine the importance of multi-step effects, nuclear
contributions, feeding from other states and corrections to the semi-classical
approximation. We study the excitation of 30S, 58Ni and 78Kr on 197Au at ~ 50
AMeV. We find that nuclear effects may contribute more than 10% and that
feeding contributions can be larger than 15%. These corrections do not alter
significantly the published B(E2) values, however an additional theoretical
error of up to 13% should be added to the experimental uncertainty if the
semi-classical model is used. This theoretical error is reduced to less than 7%
when performing a quantal coupled-channel analysis.Comment: 9 pages, accepted for publication in J. Phys. G: Nucl. Phy
Two neutron decay of 16Be
Recently, the first example of two-neutron decay from the ground state of an
unbound nucleus, Be, was seen. Three-body methods are ideal for exactly
treating the degrees of freedom important for these decays. Using a basis
expansion over hyperspherical harmonics and the hyperspherical R-matrix method,
we construct a realistic model of Be in order to investigate its decay
mode and the role of the two-neutron interaction. The neutron-Be
interaction is constrained using shell model predictions. We obtain a ground
state for Be that is over-bound by approximately 1 MeV with a width of
approximately 0.23 MeV. This suggests, that for such systems, the three-body
force needs to be repulsive.Comment: 4 pages, 1 figure, contribution to the proceedings for the 21st
International Conference on Few Body Problems in Physics, Chicago, Illinois,
US
Status of reaction theory for studying rare isotopes
Reactions are an important tool to study nuclear structure and for extracting
reactions relevant for astrophysics. In this paper we focus on deuteron induced
reactions which can provide information on neutron shell evolution as well as
neutron capture cross sections. We review recent work on the systematic
comparison of the continuum discretized coupled channel method, the adiabatic
wave approximation and the Faddeev momentum-space approach. We also explore
other aspects of the reaction mechanism and discuss in detail difficulties
encountered in the calculations.Comment: 7 pages, 5 figures, proceeding for HITES 201
Understanding low energy reaction with exotic nuclei
Recent developments on the understanding of low energy reactions are
highlighted. Emphasis is given to the CDCC framework where the breakup channels
of the projectile are included explicitly. Properties of the breakup couplings
are presented. Comments are given with regard to the separation between the
nuclear and the Coulomb contributions to breakup cross sections as well as the
dependence on the optical potentials. A discussion on the sensitivity of the
CDCC basis is discussed, by comparing pure breakup results with transfer to the
continuum calculations. Finally, some remaining controversies show the need to
go beyond the single particle picture for the projectile.Comment: Proceedings from 'Nuclei at the limits', ANL 26-30 July 2004, 6 pages
and 8 figure
Li in a Three-Body Model with Realistic Forces: Separable vs. Non-separable Approach
{\bf Background:} Deuteron induced reactions are widely used to probe nuclear
structure and astrophysical information. Those (d,p) reactions may be viewed as
three-body reactions and described with Faddeev techniques.
{\bf Purpose:} Faddeev equations in momentum space have a long tradition of
utilizing separable interactions in order to arrive at sets of coupled integral
equations in one variable. However, it needs to be demonstrated that their
solution based on separable interactions agrees exactly with solutions based on
non-separable forces.
{\bf Results:} The ground state of Li is calculated via momentum space
Faddeev equations using the CD-Bonn neutron-proton force and a Woods-Saxon type
neutron(proton)-He force. For the latter the Pauli-forbidden -wave bound
state is projected out. This result is compared to a calculation in which the
interactions in the two-body subsystems are represented by separable
interactions derived in the Ernst-Shakin-Thaler framework.
{\bf Conclusions:} We find that calculations based on the separable
representation of the interactions and the original interactions give results
that agree to four significant figures for the binding energy, provided an
off-shell extension of the EST representation is employed in both subsystems.
The momentum distributions computed in both approaches also fully agree with
each other
Scaling Behavior of Driven Interfaces Above the Depinning Transition
We study the depinning transition for models representative of each of the
two universality classes of interface roughening with quenched disorder. For
one of the universality classes, the roughness exponent changes value at the
transition, while the dynamical exponent remains unchanged. We also find that
the prefactor of the width scales with the driving force. We propose several
scaling relations connecting the values of the exponents on both sides of the
transition, and discuss some experimental results in light of these findings.Comment: Revtex 3.0, 4 pages in PRL format + 5 figures (available at
ftp://jhilad.bu.edu/pub/abbhhss/ma-figures.tar.Z ) submitted to Phys Rev Let
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