143 research outputs found
Plastic Indians, Nazis, and Genocide: A Perspective on America\u27s Treatment of Indian Nations
Landau parameters of nuclear matter in the spin and spin-isospin channels
The equation of state of spin and isospin polarized nuclear matter is
determined in the framework of the Brueckner theory including three-body
forces. The Landau parameters in the spin and spin-isospin sectors are derived
as a function of the baryonic density. The results are compared with the
Gamow-Teller collective modes. The relevance of and for neutron
stars is shortly discussed, including the magnetic susceptibility and the
neutron star cooling.Comment: 2 pages, 2 figures, RevTex4 forma
Do Hadronic Charge Exchange Reactions Measure Electroweak L = 1 Strength?
An eikonal model has been used to assess the relationship between calculated
strengths for first forbidden beta decay and calculated cross sections for
(p,n) charge exchange reactions. It is found that these are proportional for
strong transitions, suggesting that hadronic charge exchange reactions may be
useful in determining the spin-dipole matrix elements for astrophysically
interesting leptonic transitions.Comment: 14 pages, 5 figures, Submitted to Physical Review
Missing and Quenched Gamow Teller Strength
Gamow-Teller strength functions in full spaces are calculated with
sufficient accuracy to ensure that all the states in the resonance region have
been populated. Many of the resulting peaks are weak enough to become
unobservable. The quenching factor necessary to bring into agreement the low
lying observed states with shell model predictions is shown to be due to
nuclear correlations. To within experimental uncertainties it is the same that
is found in one particle transfer and (e,e') reactions. Perfect consistency
between the observed peaks and the calculation is
achieved by assuming an observation threshold of 0.75\% of the total strength,
a value that seems typical in several experimentsComment: 11 pages, 6 figures avalaible upon request, RevTeX, FTUAM-94/0
Splitting of the Dipole and Spin-Dipole Resonances
Cross sections for the 90,92,94Zr(p,n) reactions were measured at energies of
79.2 and 119.4 MeV. A phenomenological model was developed to describe the
variation with bombarding energy of the position of the L=1 peak observed in
these and other (p,n) reactions. The model yields the splitting between the
giant dipole and giant spin dipole resonances. Values of these splittings are
obtained for isotopes of Zr and Sn and for 208Pb.Comment: 14 pages, 4 figure
On the Strength of Spin-Isospin Transitions in A=28 Nuclei
The relations between the strengths of spin-isospin transition operators
extracted from direct nuclear reactions, magnetic scattering of electrons and
processes of semi-leptonic weak interactions are discussed.Comment: LaTeX, 8 pages, 1Postscript with figur
Projectile and target-Roper excitation in the p (d, d')X reaction
In this paper we compare a model that contains the mechanisms of
excitation in the projectile and Roper excitation in the target with
experimental data from two (d, d') experiments on a proton target. The
agreement of the theory with the experiment is fair for the data taken at T_d =
2.3 GeV. The excitation in the projectile is predicted close to the
observed energy with the correct width. The theory, however, underpredicts by
about 40% the cross sections measured at T_d = 1.6 GeV at angles where the
cross section has fallen by about two orders of magnitude. The analysis done
here allows to extract an approximate strength for the excitation of the Roper
[N^*(1440)] excitation and a qualitative agreement with the theoretical
predictions is also found.Comment: 8 ps figure
Gamow-Teller strength in 54Fe and 56Fe
Through a sequence of large scale shell model calculations, total
Gamow-Teller strengths ( and ) in Fe and Fe are
obtained. They reproduce the experimental values once the operator
is quenched by the standard factor of . Comparisons are made with recent
Shell Model Monte Carlo calculations. Results are shown to depend critically on
the interaction. From an analysis of the GT+ and GT strength functions it is
concluded that experimental evidence is consistent with the sum rule.Comment: 6 pages, RevTeX 3.0 using psfig, 7 Postscript figures included using
uufile
What about a beta-beam facility for low energy neutrinos?
A novel method to produce neutrino beams has recently been proposed : the
beta-beams. This method consists in using the beta-decay of boosted radioactive
nuclei to obtain an intense, collimated and pure neutrino beam. Here we propose
to exploit the beta-beam concept to produce neutrino beams of low energy. We
discuss the applications of such a facility as well as its importance for
different domains of physics. We focus, in particular, on neutrino-nucleus
interaction studies of interest for various open issues in astrophysics,
nuclear and particle physics. We suggest possible sites for a low energy
beta-beam facility.Comment: 4 pages, 1 figur
Inclusion of virtual nuclear excitations in the formulation of the (e,e'N)
A wave-function framework for the theory of the (e,e'N) reaction is presented
in order to justify the use of coupled channel equations in the usual Feynman
matrix element. The overall wave function containing the electron and nucleon
coordinates is expanded in a basis set of eigenstates of the nuclear
Hamiltonian, which contain both bound states as well as continuum states.. The
latter have an ingoing nucleon with a variable momentum Q incident on the
daughter nucleus as a target, with as many outgoing channels as desirable. The
Dirac Eqs. for the electron part of the wave function acquire inhomogeneous
terms, and require the use of distorted electron Green's functions for their
solutions. The condition that the asymptotic wave function contain only the
appropriate momentum Q_k for the outgoing nucleon, which corresponds to the
electron momentum k through energy conservation, is achieved through the use of
the steepest descent saddle point method, commonly used in three-body
calculations.Comment: 30 page
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