4,000 research outputs found
Interplay between valence and core excitation mechanisms in the breakup of halo nuclei
The phenomenon of core excitation in the breakup of a two-body halo nucleus
is investigated. We show that this effect plays a significant role in the
reaction dynamics and, furthermore, its interference with the valence
excitation mechanism has sizable and measurable effects on the breakup angular
distributions. These effects have been studied in the resonant breakup of 11Be
on a carbon target, populating the resonances at 1.78 MeV (5/2+) and 3.41 MeV
(3/2+). The calculations have been performed using a recently extension of the
DWBA method, which takes into account the effect of core excitation in both the
structure of the halo nucleus and in the reaction mechanism. The calculated
angular distributions have been compared with the available data [Fukuda et
al., Phys. Rev. C70,054606]. Although each of these resonances is dominated by
one of the two considered mechanisms, the angular patterns of these resonances
depend in a very delicate way on the interference between them. This is the
first clear evidence of this effect but the phenomenon is likely to occur in
other similar reactions.Comment: 5 pages, 2 figures, (Version to appear in Physical Review Letters
Description of the LiLi transfer reaction using structure overlaps from a full three-body model
Recent data on the differential angular distribution for the transfer
reaction Li(p,d)Li at MeV in inverse kinematics are
analysed within the DWBA reaction framework, using the overlap functions
calculated within a three-body model of Li. The weight of the different
Li configurations in the system's ground state is obtained from the
structure calculations unambiguously. The effect of the Li spin in the
calculated observables is also investigated. We find that, although all the
considered models succeed in reproducing the shape of the data, the magnitude
is very sensitive to the content of wave in the Li
ground-state wave function. Among the considered models, the best agreement
with the data is obtained when the Li ground state contains a 31\%
of wave in the -Li subsystem. Although this model takes into
account explicitly the splitting of the and resonances due to the
coupling of the wave to the spin of the core, a similar
degree of agreement can be achieved with a model in which the Li spin is
ignored, provided that it contains a similar p-wave content.Comment: 8 pages, 3 figures. Final versio
Linking structure and dynamics in reactions with Borromean nuclei: the LiLi case
One-neutron removal reactions induced by two-neutron Borromean
nuclei are studied within a Transfer-to-the-Continuum (TC) reaction framework,
which incorporates the three-body character of the incident nucleus. The
relative energy distribution of the residual unbound two-body subsystem, which
is assumed to retain information on the structure of the original three-body
projectile, is computed by evaluating the transition amplitude for different
neutron-core final states in the continuum. These transition amplitudes depend
on the overlaps between the original three-body ground-state wave function and
the two-body continuum states populated in the reaction, thus ensuring a
consistent description of the incident and final nuclei. By comparing different
Li three-body models, it is found that the LiLi
relative energy spectrum is very sensitive to the position of the and
states in Li and to the partial wave content of these
configurations within the Li ground-state wave function. The possible
presence of a low-lying resonance is discussed. The coupling of the
single particle configurations with the non-zero spin of the Li core,
which produces a spin-spin splitting of the states, is also studied. Among the
considered models, the best agreement with the available data is obtained with
a Li model that incorporates the actual spin of the core and contains
31\% of -wave content in the -Li subsystem, in accord
with our previous findings for the Li(p,d)Li transfer reaction,
and a near-threshold virtual state.Comment: 7 pages, 4 figures, submitted to PL
Investigating the 10Li continuum through 9Li(d,p)10Li reactions
The continuum structure of the unbound system Li, inferred from the
LiLi transfer reaction, is reexamined. Experimental data for
this reaction, measured at two different energies, are analyzed with the same
reaction framework and structure models. It is shown that the seemingly
different features observed in the measured excitation energy spectra can be
understood as due to the different incident energy and angular range covered by
the two experiments. The present results support the persistence of the
parity inversion beyond the neutron dripline as well as the splitting of the
well-known low-lying -wave resonance. Furthermore, they provide indirect
evidence that most of the single-particle strength, including possible
resonances, lies at relatively high excitations energies.Comment: accepted for publication in Physics Letters
Determining distributions of weakly bound nuclei from breakup cross sections using Continuum Discretized Coupled Channels calculations. Application to Be
A novel method to extract the strength of a weakly bound nucleus from
experimental Coulomb dissociation data is proposed. The method makes use of
continuum discretized coupled channels (CDCC) calculations, in which both
nuclear and Coulomb forces are taken into account to all orders. This is a
crucial advantage with respect to the standard procedure based on the
Equivalent Photon Method (EPM) which does not properly take into account
nuclear distortion, higher order coupling effects, or Coulomb-nuclear
interference terms. The procedure is applied to the Be nucleus using two
sets of available experimental data at different energies, for which seemingly
incompatible have been reported using the EPM. We show that the present
procedure gives consistent strengths, thus solving the aforementioned
long-standing discrepancy between the two measurements.Comment: Submitted for publicatio
Atmosphere above a large solar pore
A large solar pore with a granular light bridge was observed on October 15,
2008 with the IBIS spectrometer at the Dunn Solar Telescope and a 69-min long
time series of spectral scans in the lines Ca II 854.2 nm and Fe I 617.3 nm was
obtained. The intensity and Doppler signals in the Ca II line were separated.
This line samples the middle chromosphere in the core and the middle
photosphere in the wings. Although no indication of a penumbra is seen in the
photosphere, an extended filamentary structure, both in intensity and Doppler
signals, is observed in the Ca II line core. An analysis of morphological and
dynamical properties of the structure shows a close similarity to a
superpenumbra of a sunspot with developed penumbra. A special attention is paid
to the light bridge, which is the brightest feature in the pore seen in the Ca
II line centre and shows an enhanced power of chromospheric oscillations at 3-5
mHz. Although the acoustic power flux in the light bridge is five times higher
than in the "quiet" chromosphere, it cannot explain the observed brightness.Comment: 6 pages, 3 figures, accepted in Journal of Physics: Conference Serie
The effect of load in a contact with boundary lubrication
The effect of the transition load on the wear in a contact with boundary lubrication was investigated. An experimental method was developed for this purpose, and parameters affecting the boundary lubrication under industrial operating conditions were identified. These parameters are the adsorbed boundary film, the contact microgeometry (surface roughness), macrogeometry, and hardness of materials used. It was found that the curve of the tops of the surface protrustion affect the transition load, and thus the boundary lubrication. The transition load also depends on the chemical nature of the contact and its geometrical and mechanical aspects
The continuum description with pseudo-state wave functions
Benchmark calculations are performed aiming to test the use of two different
pseudo-state bases on the the Multiple Scattering expansion of the total
Transition amplitude (MST) scattering framework. Calculated differential cross
sections for p-6He inelastic scattering at 717 MeV/u show a good agreement
between the observables calculated in the two bases. This result gives extra
confidence on the pseudo-state representation of continuum states to describe
inelastic/breakup scattering.Comment: 4 pages, 2 figures. Published in Physical Review
Simultaneous analysis of elastic scattering and transfer/breakup channels for the 6He+208Pb reaction at energies near the Coulomb barrier
The elastic and alpha-production channels for the 6He+208Pb reaction are
investigated at energies around the Coulomb barrier (E_{lab}=14, 16, 18, 22,
and 27 MeV). The effect of the two-neutron transfer channels on the elastic
scattering has been studied within the Coupled-Reaction-Channels (CRC) method.
We find that the explicit inclusion of these channels allows a simultaneous
description of the elastic data and the inclusive alpha cross sections at
backward angles. Three-body Continuum-Discretized Coupled-Channels (CDCC)
calculations are found to reproduce the elastic data, but not the
transfer/breakup data. The trivially-equivalent local polarization potential
(TELP) derived from the CRC and CDCC calculations are found to explain the
features found in previous phenomenological optical model calculations for this
system.Comment: 7 pages, 6 figures (replaced with updated version
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