227 research outputs found
Determination of S17 from 8B breakup by means of the method of continuum-discretized coupled-channels
The astrophysical factor for 7Be(p,\gamma)8B at zero energy, S17(0), is
determined from an analysis of 208Pb(8B, p+7Be)208Pb at 52 MeV/nucleon by means
of the method of continuum-discretized coupled-channels (CDCC) taking account
of all nuclear and Coulomb breakup processes. The asymptotic normalization
coefficient (ANC) method is used to extract S17(0) from the calculated
breakup-cross-section. The main result of the present paper is S17(0)=20.9
+2.0/-1.9 eV b. The error consists of 8.4% experimental systematic error and
the error due to the ambiguity in the s-wave p-7Be scattering length. This
value of S17(0) differs from the one extracted with the first-order
perturbation theory including Coulomb breakup by dipole transitions: 18.9 +/-
1.8 eV b. It turns out that the difference is due to the inclusion of the
nuclear and Coulomb-quadrupole transitions and multi-step processes of
all-order in the present work. The p-7Be interaction potential used in the CDCC
calculation is also used in the ANC analysis of 7Be(p,\gamma)8B. The value of
S17(0)=21.7 +0.62/-0.55 eV b obtained is consistent with the previous one
obtained from a precise measurement of the p-capture reaction cross section
extrapolated to zero incident energy, S17(0)=22.1 +/- 0.6 (expt) +/- 0.6 (theo)
eV b, where (theo) stands for the error in the extrapolation. Thus, the
agreement between the values of S17(0) obtained from direct 7Be(p,\gamma)8B and
indirect 8B-breakup measurements is significantly improved.Comment: 13 pages, 9 figures, published in PR
Continuum-discretized coupled-channels method for four-body breakup reactions
Development of the method of CDCC (Continuum-Discretized Coupled-Channels)
from the level of three-body CDCC to that of four-body CDCC is reviewed.
Introduction of the pseudo-state method based on the Gaussian expansion method
for discretizing the continuum states of two-body and three-body projectiles
plays an essential role in the development. Furthermore, introduction of the
complex-range Gaussian basis functions is important to improve the CDCC for
nuclear breakup so as to accomplish that for Coulomb and nuclear breakup. A
successful application of the four-body CDCC to He+C scattering at
18 and 229.8 MeV is reported.Comment: Latex file of revtex4 class, 14 pages, 10 figures. A talk given at
the Workshop on Reaction Mechanisms for Rare Isotope Beams, Michigan State
University, March 9-12, 2005 (to appear in an AIP Conference Proceedings
Laws of the media, their environments and their users: The flip of the artifact, of its ground and its user
Marshall McLuhan’s Laws of Media (LOM), which describe the evolution of artifacts in terms of enhancement, obsolescence, retrieval and reversal (or flip) are extended to create Laws of Media Environments (LOME) and Laws of Media Users (LOMU). It is shown that the environment or ground in which the figures of the artifacts in the LOM operate and the users of those artifacts undergo respectively a similar evolution of enhancement, obsolescence, retrieval and reversal paralleling McLuhan’s original LOM
Coulomb breakup effects on the elastic cross section of He+Bi scattering near Coulomb barrier energies
We accurately analyze the He+Bi scattering at 19 and 22.5 MeV
near the Coulomb barrier energy, using the continuum-discretized
coupled-channels method (CDCC) based on the ++He+Bi four-body
model.
The three-body breakup continuum of He is discretized by diagonalizing
the internal Hamiltonian of He in a space spanned by the Gaussian basis
functions.
The calculated elastic and total reaction cross sections are in good
agreement with the experimental data, while the CDCC calculation based on the
di-neutron model of He, i.e., the +He+Bi three-body
model, does not reproduce the data.Comment: 5 pages, 5 figures, uses REVTeX 4, submitted to Phys. Rev.
Polarization phenomena in hyperon-nucleon scattering
We investigate polarization observables in hyperon-nucleon scattering by
decomposing scattering amplitudes into spin-space tensors, where each component
describes scattering by corresponding spin-dependent interactions, so that
contributions of the interactions in the observables are individually
identified. In this way, for elastic scattering we find some linear
combinations of the observables sensitive to particular spin-dependent
interactions such as symmetric spin-orbit (LS) interactions and antisymmetric
LS ones. These will be useful to criticize theoretical predictions of the
interactions when the relevant observables are measured. We treat vector
analyzing powers, depolarizations, and coefficients of polarization transfers
and spin correlations, a part of which is numerically examined in scattering as an example. Total cross sections are studied for polarized
beams and targets as well as for unpolarized ones to investigate spin
dependence of imaginary parts of forward scattering amplitudes.Comment: 15 pages, 8 figure
Continuum-discretized coupled-channels method for four-body nuclear breakup in He+C scattering
We propose a fully quantum-mechanical method of treating four-body nuclear
breakup processes in scattering of a projectile consisting of three
constituents, by extending the continuum-discretized coupled-channels method.
The three-body continuum states of the projectile are discretized by
diagonalizing the internal
Hamiltonian of the projectile with the Gaussian basis functions. For
He+C scattering at 18 and 229.8 MeV, the validity of the method is
tested by convergence of the elastic and breakup cross sections with respect to
increasing the number of the basis functions. Effects of the four-body breakup
and the Borromean structure of He on the elastic and total reaction cross
sections are discussed.Comment: 5 pages, 6 figures, uses REVTeX 4, submitted to Phys. Rev.
Central and tensor components of three-nucleon forces in low-energy proton-deuteron scattering
Contributions of three-nucleon forces (3NF) to proton-deuteron scattering
observables at energies below the deuteron breakup threshold are studied by
solving the Faddeev equation that includes the Coulomb interaction. At E_p=3.0
MeV, we find that the central part of a two-pion exchange 3NF removes the
discrepancy between measured cross sections and the calculated ones by
two-nucleon forces, and improves the agreement with T_{22} experimental data.
However, the tensor part of the 3NF fails in reproducing data of the analyzing
power T_{21} by giving worse agreement between the measured and the calculated.
Detailed examinations of scattering amplitudes suggest that a P-wave
contribution in spin quartet tensor amplitudes has unsuitable sign for
reproducing the T_{21} data.Comment: 6 pages, 6 figure
New treatment of breakup continuum in the method of continuum discretized coupled channels
A new method of pseudo-state discretization is proposed for the method of
continuum discretized coupled channels (CDCC) to deal with three-body breakup
processes. We propose real- and complex-range Gaussian bases for the
pseudo-state wave functions, and show that they form in good approximation a
complete set in the configuration space which is important for breakup
processes.
Continuous S-matrix elements are derived with the approximate completeness
from discrete ones calculated by CDCC.
Accuracy of the method is tested quantitatively for two realistic examples,
d+Ni scattering at 80 MeV and Li+Ca scattering at 156 MeV
with the satisfactory results. Possibility of application of the method to
four-body breakup processes is also discussed.Comment: 10 pages, 14 Postscript figures, uses REVTeX 4, submitted to Phys.
Rev.
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