202 research outputs found
Cluster Model for Near-barrier Fusion Induced by Weakly Bound and Halo Nuclei
The influence on the fusion process of coupling transfer/breakup channels is
investigated for the medium weight Li+Co systems in the vicinity
of the Coulomb barrier. Coupling effects are discussed within a comparison of
predictions of the Continuum Discretized Coupled-Channels model. Applications
to He+Co induced by the borromean halo nucleus He are also
proposed.Comment: 5 pages, 3 figures, FINUSTAR2 Conference, Aghios Nikolaus, Crete,
Greece. 10-14 September 200
The reaction 13C(alpha,n)16O: a background for the observation of geo-neutrinos
The absolute cross section of the C(,n)O reaction has
been measured at E = 0.8 to 8.0 MeV with an overall accuracy of 4%.
The precision is needed to subtract reliably a background in the observation of
geo-neutrinos, e.g. in the KamLAND detector.Comment: LaTex file, 13 pages including 3 ps figures. Any request to
[email protected]. Phys. Rev . C, to appea
Proton induced reaction cross section measurements on Se isotopes for the astrophysical p process
As a continuation of a systematic study of reactions relevant to the
astrophysical p process, the cross sections of the 74,76Se(p,gamma)75,77Br and
82Se(p,n)82Br reactions have been measured at energies from 1.3 to 3.6 MeV
using an activation technique. The results are compared to the predictions of
Hauser-Feshbach statistical model calculations using the NON-SMOKER and MOST
codes. The sensitivity of the calculations to variations in the optical proton
potential and the nuclear level density was studied. Good agreement between
theoretical and experimental reaction rates was found for the reactions
74Se(p,gamma)75Br and 82Se(p,n)82Br.Comment: 9 pages, 6 figures (in 12 eps files), accepted for publication in
Phys. Rev C, RevTeX styl
Nanoscale processes during the interaction of aluminosilicate and carbonate mineral surfaces with acid mine drainage (AMD)
Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu
Extraction of thermal and electromagnetic properties in 45Ti
The level density and gamma-ray strength function of 45Ti have been
determined by use of the Oslo method. The particle-gamma coincidences from the
46Ti(p,d gamma)45Ti pick-up reaction with 32 MeV protons are utilized to obtain
gamma-ray spectra as function of excitation energy. The extracted level density
and strength function are compared with models, which are found to describe
these quantities satisfactorily. The data do not reveal any single-particle
energy gaps of the underlying doubly magic 40Ca core, probably due to the
strong quadruple deformation
Isospin Character of the Pygmy Dipole Resonance in 124Sn
The pygmy dipole resonance has been studied in the proton-magic nucleus 124Sn
with the (a,a'g) coincidence method at E=136 MeV. The comparison with results
of photon-scattering experiments reveals a splitting into two components with
different structure: one group of states which is excited in (a,a'g) as well as
in (g,g') reactions and a group of states at higher energies which is only
excited in (g,g') reactions. Calculations with the self-consistent relativistic
quasiparticle time-blocking approximation and the quasiparticle phonon model
are in qualitative agreement with the experimental results and predict a
low-lying isoscalar component dominated by neutron-skin oscillations and a
higher-lying more isovector component on the tail of the giant dipole
resonance
Partial level density of the n-quasiparticle excitations in the nuclei of the 39< A <201 region
Level density and radiative strength functions are obtained from the analysis
of two-step cascades intensities following the thermal neutrons capture. The
data on level density are approximated by the sum of the partial level
densities corresponding to n quasiparticles excitation. The most probable
values of the collective enhancement factor of the level density are found
together with the thresholds of the next Cooper nucleons pair breaking. These
data allow one to calculate the level density of practically any nucleus in
given spin window in the framework of model concepts, taking into account all
known nuclear excitation types. The presence of an approximation results
discrepancy with theoretical statements specifies the necessity of rather
essentially developing the level density models. It also indicates the
possibilities to obtain the essentially new information on nucleon correlation
functions of the excited nucleus from the experiment.Comment: 29 pages, 8 figures, 2 table
Proton capture cross section of Sr isotopes and their importance for nucleosynthesis of proton-rich nuclides
The (p,) cross sections of three stable Sr isotopes have been
measured in the astrophysically relevant energy range. These reactions are
important for the -process in stellar nucleosynthesis and, in addition, the
reaction cross sections in the mass region up to 100 are also of importance
concerning the -process associated with explosive hydrogen and helium
burning. It is speculated that this -process could be responsible for a
certain amount of -nuclei in this mass region. The (p,) cross
sections of Sr isotopes were determined using an activation
technique. The measurements were carried out at the 5 MV Van de Graaff
accelerator of the ATOMKI, Debrecen. The resulting cross sections are compared
with the predictions of statistical model calculations. The predictions are in
good agreement with the experimental results for Sr(p,)Y
whereas the other two reactions exhibit differences that increase with mass
number. The corresponding astrophysical reaction rates have also been computed.Comment: Phys. Rev. C in pres
The pygmy quadrupole resonance and neutron-skin modes in Sn-124
We present an extensive experimental study of the recently predicted pygmy quadrupole resonance (PQR) in Sn isotopes, where complementary probes were used. In this study, and experiments were performed on 124Sn. In both reactions, states below an excitation energy of 5 MeV were populated. The E2 strength integrated over the full transition densities could be extracted from the experiment, while the experiment at the chosen kinematics strongly favors the excitation of surface modes because of the strong α-particle absorption in the nuclear interior. The excitation of such modes is in accordance with the quadrupole-type oscillation of the neutron skin predicted by a microscopic approach based on self-consistent density functional theory and the quasiparticle-phonon model (QPM). The newly determined γ-decay branching ratios hint at a non-statistical character of the E2 strength, as it has also been recently pointed out for the case of the pygmy dipole resonance (PDR). This allows us to distinguish between PQR-type and multiphonon excitations and, consequently, supports the recent first experimental indications of a PQR in 124Sn
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