1,706 research outputs found
Microscopic study of 4-alpha-particle condensation with proper treatment of resonances
The 4-alpha condensate state for ^{16}O is discussed with the THSR
(Tohsaki-Horiuchi-Schuck-Roepke) wave function which has alpha-particle
condensate character. Taking into account a proper treatment of resonances, it
is found that the 4-alpha THSR wave function yields a fourth 0^+ state in the
continuum above the 4-alpha-breakup threshold in addition to the three 0^+
states obtained in a previous analysis. It is shown that this fourth 0^+
((0_4^+)_{THSR}) state has an analogous structure to the Hoyle state, since it
has a very dilute density and a large component of alpha+^{12}C(0_2^+)
configuration. Furthermore, single-alpha motions are extracted from the
microscopic 16-nucleon wave function, and the condensate fraction and momentum
distribution of alpha particles are quantitatively discussed. It is found that
for the (0_4^+)_{THSR} state a large alpha-particle occupation probability
concentrates on a single-alpha 0S orbit and the alpha-particle momentum
distribution has a delta-function-like peak at zero momentum, both indicating
that the state has a strong 4-alpha condensate character. It is argued that the
(0_4^+)_{THSR} state is the counterpart of the 0_6^+ state which was obtained
as the 4-alpha condensate state in the previous 4-alpha OCM (Orthogonality
Condition Model) calculation, and therefore is likely to correspond to the
0_6^+ state observed at 15.1 MeV.Comment: 16 pages, 15 figures, submitted to PRC
Ab initio study of the photoabsorption of He
There are some discrepancies in the low energy data on the photoabsorption
cross section of He. We calculate the cross section with realistic nuclear
forces and explicitly correlated Gaussian functions. Final state interactions
and two- and three-body decay channels are taken into account. The cross
section is evaluated in two methods: With the complex scaling method the total
absorption cross section is obtained up to the rest energy of a pion, and with
the microscopic -matrix method both cross sections He()H
and He()He are calculated below 40\,MeV. Both methods give
virtually the same result. The cross section rises sharply from the H+
threshold, reaching a giant resonance peak at 26--27\,MeV. Our calculation
reproduces almost all the data above 30\,MeV. We stress the importance of
H+ and He+ cluster configurations on the cross section as well as
the effect of the one-pion exchange potential on the photonuclear sum rule.Comment: 15 pages, 12 figure
Peculiar properties of the cluster-cluster interaction induced by the Pauli exclusion principle
Role of the Pauli principle in the formation of both the discrete spectrum
and multi-channel states of the binary nuclear systems composed of clusters is
studied in the Algebraic Version of the resonating-group method. Solutions of
the Hill-Wheeler equations in the discrete representation of a complete basis
of the Pauli-allowed states are discussed for 4He+n, 3H+3H, and 4He+4He binary
systems. An exact treatment of the antisymmetrization effects are shown to
result in either an effective repulsion of the clusters, or their effective
attraction. It also yields a change in the intensity of the centrifugal
potential. Both factors significantly affect the scattering phase behavior.
Special attention is paid to the multi-channel cluster structure 6He+6He as
well as to the difficulties arising in the case when the two clustering
configurations, 6He+6He and 4He+8He, are taken into account simultaneously. In
the latter case the Pauli principle, even in the absence of a potential energy
of the cluster-cluster interaction, leads to the inelastic processes and
secures an existence of both the bound state and resonance in the 12Be compound
nucleus.Comment: 17 pages, 14 figures, 1 table; submitted to Phys.Rev.C Keywords:
light neutron-rich nuclei, cluster model
The {\alpha}-Decay Chains of the Isotopes using Relativistic Mean Field Theory
We study the binding energy, root-mean-square radius and quadrupole
deformation parameter for the synthesized superheavy element Z = 115, within
the formalism of relativistic mean field theory. The calculation is dones for
various isotopes of Z = 115 element, starting from A = 272 to A = 292. A
systematic comparison between the binding energies and experimental data is
made.The calculated binding energies are in good agreement with experimental
result. The results show the prolate deformation for the ground state of these
nuclei. The most stable isotope is found to be 282115 nucleus (N = 167) in the
isotopic chain. We have also studied Q{\alpha} and T{\alpha} for the
{\alpha}-decay chains of 115.Comment: 12 Pages 6 Figures 3 Table
Isoscalar monopole excitations in O: -cluster states at low energy and mean-field-type states at higher energy
Isoscalar monopole strength function in O up to MeV is
discussed. We found that the fine structures at the low energy region up to
MeV in the experimental monopole strength function obtained
by the O reaction can be rather satisfactorily
reproduced within the framework of the cluster model, while the gross
three bump structures observed at the higher energy region ( MeV) look likely to be approximately reconciled by the mean-field
calculations such as RPA and QRPA. In this paper, it is emphasized that two
different types of monopole excitations exist in O; one is the monopole
excitation to cluster states which is dominant in the lower energy part ( MeV), and the other is the monopole excitation of the mean-field
type such as one-particle one-hole () which {is attributed} mainly to the
higher energy part ( MeV). It is found that this
character of the monopole excitations originates from the fact that the ground
state of O with the dominant doubly closed shell structure has a duality
of the mean-field-type {as well as} -clustering {character}. This dual
nature of the ground state seems to be a common feature in light nuclei.Comment: 35 pages, 5 figure
The Diffuse Supernova Neutrino Background is detectable in Super-Kamiokande
The Diffuse Supernova Neutrino Background (DSNB) provides an immediate
opportunity to study the emission of MeV thermal neutrinos from core-collapse
supernovae. The DSNB is a powerful probe of stellar and neutrino physics,
provided that the core-collapse rate is large enough and that its uncertainty
is small enough. To assess the important physics enabled by the DSNB, we start
with the cosmic star formation history of Hopkins & Beacom (2006) and confirm
its normalization and evolution by cross-checks with the supernova rate,
extragalactic background light, and stellar mass density. We find a sufficient
core-collapse rate with small uncertainties that translate into a variation of
+/- 40% in the DSNB event spectrum. Considering thermal neutrino spectra with
effective temperatures between 4-6 MeV, the predicted DSNB is within a factor
4-2 below the upper limit obtained by Super-Kamiokande in 2003. Furthermore,
detection prospects would be dramatically improved with a gadolinium-enhanced
Super-Kamiokande: the backgrounds would be significantly reduced, the fluxes
and uncertainties converge at the lower threshold energy, and the predicted
event rate is 1.2-5.6 events /yr in the energy range 10-26 MeV. These results
demonstrate the imminent detection of the DSNB by Super-Kamiokande and its
exciting prospects for studying stellar and neutrino physics.Comment: 14 pages, 5 figures, 4 tables, some added discussions, accepted for
publication in Physical Review
Variational Calculations of the Nucleus Structure in a 3 Model Using a Deep Potential with Forbidden States
The energy spectrum of the nucleus with and
is investigated in the framework of the multicluster dynamical model
by using a deep -potential with forbidden states in the S and D
waves. A very high sensitivity of the compact ground and first excited
states energy levels to the description of the two-body forbidden states wave
functions has been estabilished. It is shown also that the chosen method of
orthogonalizing pseudopotentials yields convergent results for the energies of
the excited and states of the nucleus with a
well developed cluster like structure
A Comparative Study of the Parker Instability under Three Models of the Galactic Gravity
To examine how non-uniform nature of the Galactic gravity might affect length
and time scales of the Parker instability, we took three models of gravity,
uniform, linear and realistic ones. To make comparisons of the three gravity
models on a common basis, we first fixed the ratio of magnetic pressure to gas
pressure at = 0.25, that of cosmic-ray pressure at = 0.4, and
the rms velocity of interstellar clouds at = 6.4 km s, and then
adjusted parameters of the gravity models in such a way that the resulting
density scale heights for the three models may all have the same value of 160
pc. Performing linear stability analyses onto equilibrium states under the
three models with the typical ISM conditions, we calculate the maximum growth
rate and corresponding length scale for each of the gravity models. Under the
uniform gravity the Parker instability has the growth time of 1.2
years and the length scale of 1.6 kpc for symmetric mode. Under the realistic
gravity it grows in 1.8 years for both symmetric and
antisymmetric modes, and develops density condensations at intervals of 400 pc
for the symmetric mode and 200 pc for the antisymmetric one. A simple change of
the gravity model has thus reduced the growth time by almost an order of
magnitude and its length scale by factors of four to eight. These results
suggest that an onset of the Parker instability in the ISM may not necessarily
be confined to the regions of high and .Comment: Accepted for publication in ApJ, using aaspp4.sty, 18 text pages with
9 figure
Proton inelastic scattering to continuum studied with antisymmetrized molecular dynamics
Intermediate energy (p,px) reaction is studied with antisymmetrized
molecular dynamics (AMD) in the cases of Ni target with MeV
and C target with 200 and 90 MeV. Angular distributions for
various energies are shown to be reproduced well without any
adjustable parameter, which shows the reliability and usefulness of AMD in
describing light-ion reactions. Detailed analyses of the calculations are made
in the case of Ni target and following results are obtained: Two-step
contributions are found to be dominant in some large angle region and to be
indispensable for the reproduction of data. Furthermore the reproduction of
data in the large angle region \theta \agt 120^\circ for = 100 MeV
is shown to be due to three-step contributions. Angular distributions for
E_{p'} \agt 40 MeV are found to be insensitive to the choice of different
in-medium nucleon-nucleon cross sections and the reason of this
insensitivity is discussed in detail. On the other hand, the total reaction
cross section and the cross section of evaporated protons are found to be
sensitive to . In the course of the analyses of the calculations,
comparison is made with the distorted wave approach.Comment: 16 pages, 7 Postscript figure
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