419 research outputs found
Analysis of fusion-fission dynamics by pre-scission neutron emission in Ni+Pb
We analyzed the experimental data of the pre-scission neutron multiplicity in
connection with fission fragments in the reaction Ni+Pb at the
incident energy corresponding to the excitation energy of compound nucleus
=185.9 MeV, which was performed by D\'{e}MoN group. The relation between
the pre-scission neutron multiplicity and each reaction process having
different reaction time is investigated. In order to study the fusion-fission
process accompanied by neutron emission, the fluctuation-dissipation model
combined with a statistical model is employed. It is found that the
fusion-fission process and the quasi-fission process are clearly distinguished
in correlation with the pre-scission neutron multiplicity.Comment: 11 figure
High-spin structures of 88Kr and 89Rb: Evolution from collective to single-particle behaviors
The high-spin states of the two neutron-rich nuclei, 88Kr and 89R have been
studied from the 18O + 208Pb fusion-fission reaction. Their level schemes were
built from triple gamma-ray coincidence data and gamma-gamma angular
correlations were analyzed in order to assign spin and parity values to most of
the observed states. The two levels schemes evolve from collective structures
to single-particle excitations as a function of the excitation energy.
Comparison with results of shell-model calculations gives the specific proton
and neutron configurations which are involved to generate the angular momentum
along the yrast lines.Comment: 12 pages, 9 figures, Physical Review C (2013) in pres
Evolution of shell structure in neutron-rich calcium isotopes
We employ interactions from chiral effective field theory and compute the
binding energies and low-lying excitations of calcium isotopes with the
coupled-cluster method. Effects of three-nucleon forces are included
phenomenologically as in-medium two-nucleon interactions, and the coupling to
the particle continuum is taken into account using a Berggren basis. The
computed ground-state energies and the low-lying 2+ states for the isotopes
42,48,50,52Ca are in good agreement with data, and we predict the excitation
energy of the first 2+ state in 54Ca at 1.9 MeV, displaying only a weak
sub-shell closure. In the odd-mass nuclei 53,55,61Ca we find that the positive
parity states deviate strongly from the naive shell model.Comment: 5 pages, 4 figures; small correction of effective 3NF and slight
change of the corresponding parameters; updated figures and tables; main
results and conclusions unchange
High-spin structures of 136Cs
Odd-odd 136Cs nuclei have been produced in the 18O + 208Pb and 12C + 238U
fusion-fission reactions and their gamma rays studied with the Euroball array.
The high-spin level scheme has been built up to ~ 4.7 MeV excitation energy and
spin I ~ 16 hbar from the triple gamma-ray coincidence data. The configurations
of the three structures observed above ~ 2 MeV excitation energy are first
discussed by analogy with the proton excitations identified in the semi-magic
137Cs nucleus, which involve the three high-j orbits lying above the Z=50 gap,
pi g_{7/2}, pi d_{5/2} and pi h_{11/2}. This is confirmed by the results of
shell-model calculations performed in this work.Comment: 6 pages, 4 figures, 3 table
8Be cluster emission versus alpha evaporation in 28Si + 12C
The possible occurence of highly deformed configurations in the Ca
di-nuclear system formed in the Si + C reaction is investigated
by analyzing the spectra of emitted light charged particles. Both inclusive and
exclusive measurements of the heavy fragments (A 10) and their
associated light charged particles (protons and particles) have been
made at the IReS Strasbourg {\sc VIVITRON} Tandem facility at bombarding
energies of (Si) = 112 MeV and 180 MeV by using the {\sc
ICARE} charged particle multidetector array. The energy spectra, velocity
distributions, in-plane and out-of-plane angular correlations of light charged
particles are compared to statistical-model calculations using a consistent set
of parameters with spin-dependent level densities. This spin dependence
approach suggests the onset of large nuclear deformation in Ca at high
spin. This conclusion might be connected with the recent observation of
superdeformed bands in the Ca nucleus. The analysis of
particles in coincidence with S fragments suggests a surprisingly strong
Be cluster emission of a binary nature.Comment: 39 pages 15 figure
Search for emission of unstable Be clusters from hot Ca and Ni nuclei
The possible occurence of highly deformed configurations is investigated in
the Ca and Ni di-nuclear systems as formed in the Si +
C and Si + Si reactions, respectively, by using the
properties of emitted light charged particles. Inclusive as well as exclusive
data of the heavy fragments (A 6) and their associated light charged
particles (p, d, t, and -particles) have been collected at the IReS
Strasbourg VIVITRON Tandem facility with two bombarding energies
Si) = 112 and 180 MeV by using the ICARE charged particle
multidetector array, which consists of nearly 40 telescopes. The measured
energy spectra, velocity distributions, in-plane and out-of-plane angular
correlations are analysed by Monte Carlo CASCADE statistical-model calculations
using a consistent set of parameters with spin-dependent level densities.
Although significant deformation effects at high spin are needed, the remaining
disagreement observed in the Si + C reaction for the S
evaporation residue suggests an unexpected large unstable Be cluster
emission of a binary nature.Comment: 13 pages latex, 9 eps figures. Paper presented at the XXXIX
International Winter Meeting on Nuclear Physics, Bormio(Italy) January 22-27,
2001 (to be published at Ricerca Scientifica ed Educazione Permanente
Large Deformation Effects in the N = Z 44Ti Compound Nucleus
The N = Z 44Ti* nucleus has been populated in Fusion Evaporation process at
very high excitation energies and angular momenta using two entrance channels
with different mass-asymmetry. The deformation effects in the rapidly rotating
nuclei have been investigated through the energy distribution of the
alpha-particle combined to statistical-model calculations. In the case of
low-multiplicity events, the ratio between first particle emitted has been
measured and shows significant disagreement with the predictions of the
statistical-model. This may explain The large discrepancies observed in proton
energy spectra measured in previous experiments performed in the same mass
region.Comment: Proceeding of the 10th International Conference on Nuclear Reaction
Mechanisms, Varenna Italy, June 9-13 2003. 10 pages, 6 figures, 1 tabl
High-spin states with seniority v=4,4,6 in 119-126Sn
The 119-126Sn nuclei have been produced as fission fragments in two reactions
induced by heavy ions: 12C+238U at 90 MeV bombarding energy, 18O+208Pb at 85
MeV. Their level schemes have been built from gamma rays detected using the
Euroball array. High-spin states located above the long-lived isomeric states
of the even- and odd-A 120-126Sn nuclei have been identified. Moreover isomeric
states lying around 4.5 MeV have been established in 120,122,124,126Sn from the
delayed coincidences between the fission fragment detector SAPhIR and the
Euroball array. The states located above 3-MeV excitation energy are ascribed
to several broken pairs of neutrons occupying the nu h11/2 orbit. The maximum
value of angular momentum available in such a high-j shell, i.e. for
mid-occupation and the breaking of the three neutron pairs, has been
identified. This process is observed for the first time in spherical nuclei.Comment: 20 pages, 22 figures, 12 tables, accepted for publication in Physical
Review
Isomeric states in No
6 pagesInternational audienceIsomeric states in 253No have been investigated by conversion-electron and gamma-ray spectroscopy with the GABRIELA detection system. The 31 micro second isomer reported more than 30 years ago is found to decay to the ground state of 253No by the emission of a 167 keV M2 transition. The spin and parity of this low-lying isomeric state are established to be 5/2+. The presence of another longer-lived isomeric state is also discussed
Deformation effects in the Si+C and Si+Si reaction Search
The possible occurence of highly deformed configurations is investigated in
the Ca and Ni di-nuclear systems as formed in the
Si+C,Si reactions by using the properties of emitted light
charged particles. Inclusive as well as exclusive data of the heavy fragments
and their associated light charged particles have been collected by using the
{\sc ICARE} charged particle multidetector array. The data are analysed by
Monte Carlo CASCADE statistical-model calculations using a consistent set of
parameters with spin-dependent level densities. Significant deformation effects
at high spin are observed as well as an unexpected large Be cluster
emission of a binary nature.Comment: 3 pages latex, 2 eps figures, paper presented in "wokshop on physics
with multidetector array (pmda2000)Calcutta, India (to be published at
PRAMANA, journal of Physics, India
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