141 research outputs found
Computation of the electron beam quality factors for the NE2571, NE2571A and NE2581A thimble ionization chambers using PENELOPE
The quality correction factor for electron beams was calculated
for three thimble ionization chambers, namely, NE2571, NE2571A and NE2581A. The
Monte Carlo code PENELOPE was used to estimate the overall correction factor
of these chambers for electron beams with nominal energies
ranging between 6 and 22 MeV, corresponding to a Varian Clinac 2100 C/D. A
Co beam was used as reference quality . Also eight
monoenergetic electron beams reproducing the quality index of the
Clinac beams were considered. The factors were calculated as the
ratio between and . Those obtained for the
NE2571 ionization chamber show a nice agreement with those calculated by Muir
and Rogers with EGSnrc. As it occurred to other ionization chambers analyzed in
previous works, the factors found for the monoenergetic beams
are larger (smaller) than those corresponding to the Clinac beams at low (high)
values, the differences being slightly above . Finally, the
factors obtained in the case of the NE2571A chamber are
systematically ~0.5% below those of its predecessor chamber, the NE2571.Comment: 8 pages, 2 figures, 3 table
Radiative pion capture in nuclei: a continuum shell-model approach
The radiative pion capture process in nuclei is approached by using a
continuum shell-model description of the nucleus, together with a
phenomenological treatment of the two particle-two hole effects. It is found
that these effects play an important role to reproduce the observed
experimental photon energy distribution. This distribution as well as the
integrated one depends significantly on the details of the mean field
potential. This makes this process interesting to investigate the nuclear
structure dynamics.Comment: 21 pages, LateX file + 5 figures, epsf.st
Charge-exchange excitations with finite range interactions including tensor terms
We study charge-exchange excitations in doubly magic-nuclei by using a
self-consistent Hartree-Fock plus Random Phase Approximation model. We use four
Gogny-like finite-range interactions, two of them containing tensor forces. We
investigate the effects of the various parts of the tensor forces in the two
computational steps of our model, and we find that their presence is not
negligible and improves the agreement with the experimental data.Comment: 17 pages, 5 figures, 8 table
Self-consistent Continuum Random Phase Approximation calculations with finite-range interactions
We present a technique which allows us to solve the Random Phase
Approximation equations with finite-range interactions and treats the continuum
part of the excitation spectrum without approximations. The interaction used in
the Hartree-Fock calculations to generate the single particle basis is also
used in the Continuum Random Phase Approximation calculations. We present
results for the electric dipole and quadrupole excitations in the O,
O, O, Ca, Ca and Ca nuclei. We compare our
results with those of the traditional discrete Random Phase Approximation, with
the continuum mean-field results and with the results obtained by a
phenomenological approach. We study the relevance of the continuum, of the
residual interaction and of the self-consistency. We also compare our results
with the available total photoabsorption cross section data. We compare our
photoabsorption cross section in He with that obtained by a calculation
which uses a microscopic interaction.Comment: 25 pages, 14 figs., 4 tables, accepted for publication in Physical
Review
A study of self-consistent Hartree-Fock plus Bardeen-Cooper-Schrieffer calculations with finite-range interactions
In this work we test the validity of a Hartree-Fock plus
Bardeen-Cooper-Schrieffer model in which a finite-range interaction is used in
the two steps of the calculation by comparing the results obtained to those
found in a fully self-consistent Hartree-Fock-Bogoliubov calculations using the
same interaction.Specifically, we consider the Gogny-type D1S and D1M forces.
We study a wide range of spherical nuclei, far from the stability line, in
various regions of the nuclear chart, from oxygen to tin isotopes. We calculate
various quantities related to the ground state properties of these nuclei, such
as binding energies, radii, charge and density distributions and elastic
electron scattering cross sections. The pairing effects are studied by direct
comparison with the Hartree-Fock results. Despite of its relative simplicity,
in most of the cases, our model provides results very close to those of the
Hartree-Fock-Bogoliubov calculations, and it reproduces rather well the
empirical evidences of pairing effects in the nuclei investigated.Comment: 28 pages, 13 figures. Accepted for publication in J. Phys.
Matter distribution and spin-orbit force in spherical nuclei
We investigate the possibility that some nuclei show density distributions
with a depletion in the center, a semi-bubble structure, by using a
Hartree-Fock plus Bardeen-Cooper-Schrieffer approach. We separately study the
proton, neutron and matter distributions in 37 spherical nuclei mainly in the
shell region. We found a relation between the semi-bubble structure and
the energy splitting of spin-orbit partner single particle levels. The presence
of semi-bubble structure reduces this splitting, and we study its consequences
on the excitation spectrum of the nuclei under investigation by using a
quasi-particle random-phase-approximation approach. The excitation energies of
the low-lying states can be related to the presence of semi-bubble
structure in nuclei.Comment: 15 pages, 7 tables, 11 figures. Version accepted for publication in
Phys. Rev. C; the number of nuclei analysed has been reduced; some figure
have bee redrawn, and a new figure and some references have been adde
A model of short-range correlations in the charge response
The validity of a model treating the short-range correlations up to the first
order is studied by calculating the charge response of an infinite system and
comparing the obtained results with those of a Fermi Hypernetted Chain
calculation.Comment: 6 pages, 3 Postscript figures, to be published on Phys. Rev.
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