373 research outputs found
Complementary optical-potential analysis of alpha-particle elastic scattering and induced reactions at low energies
A previously derived semi-microscopic analysis based on the Double Folding
Model, for alpha-particle elastic scattering on A~100 nuclei at energies below
32 MeV, is extended to medium mass A ~ 50-120 nuclei and energies from ~13 to
50 MeV. The energy-dependent phenomenological imaginary part for this
semi-microscopic optical model potential was obtained including the dispersive
correction to the microscopic real potential, and used within a concurrent
phenomenological analysis of the same data basis. A regional parameter set for
low-energy alpha-particles entirely based on elastic-scattering data analysis
was also obtained for nuclei within the above-mentioned mass and energy ranges.
Then, an ultimate assessment of (alpha,gamma), (alpha,n) and (alpha,p) reaction
cross sections concerned target nuclei from 45Sc to 118Sn and incident energies
below ~12 MeV. The former diffuseness of the real part of optical potential as
well as the surface imaginary-potential depth have been found responsible for
the actual difficulties in the description of these data, and modified in order
to obtain an optical potential which describe equally well both the low energy
elastic-scattering and induced-reaction data of alpha-particles.Comment: 46 pages, 16 figures. n_TOF Collaboration Annual Meeting, Bari,
Italy, 28-30 November 2007
(http://www.cern.ch/ntof/Documents/bari_nov07/bari_slides.php); revised
version accepted for publication in ADND
Rotating hyperdeformed quasi-molecular states formed in capture of light nuclei and in collision of very heavy ions
International audienceWithin a rotational liquid drop model including the nuclear proximity energy the l-dependent potential barriers governing the capture reactions of light nuclei and of very heavy ions have been determined. Rotating quasi-molecular hyperdeformed states appear at high angular momenta. The energy range of these very deformed high spin states is given for light systems. The same approach explains the observation of ternary cluster decay from56Ni and 60Zn through hyperdeformed shapes at angular momenta around 45 . The apparently observed superheavy nuclear systems in the U+Ni and U+Ge reactions at high excitation energy might correspond to these rotating isomeric states formed at very high angular momenta even though the shell effects vanish
From the stable to the exotic: clustering in light nuclei
A great deal of research work has been undertaken in alpha-clustering study
since the pioneering discovery of 12C+12C molecular resonances half a century
ago. Our knowledge on physics of nuclear molecules has increased considerably
and nuclear clustering remains one of the most fruitful domains of nuclear
physics, facing some of the greatest challenges and opportunities in the years
ahead. The occurrence of "exotic" shapes in light N=Z alpha-like nuclei is
investigated. Various approaches of the superdeformed and hyperdeformed bands
associated with quasimolecular resonant structures are presented. Evolution of
clustering from stability to the drip-lines is examined: clustering aspects
are, in particular, discussed for light exotic nuclei with large neutron excess
such as neutron-rich Oxygen isotopes with their complete spectroscopy.Comment: 15 pages, 5 figures, Presented at the International Symposium on "New
Horizons in Fundamental Physics - From Neutrons Nuclei via Superheavy
Elements and Supercritical Fields to Neutron Stars and Cosmic Rays" held at
Makutsi Safari Farm, South Africa, December 23-29, 2015. arXiv admin note:
substantial text overlap with arXiv:1402.6590, arXiv:1303.0960,
arXiv:1408.0684, arXiv:1011.342
Optical potentials for alpha particles on heavy nuclei around the Coulomb barrier
A previously semi-microscopic analysis of the -particle interaction with 50 A 124 target nuclei at energies from 8 to 50 MeV, based on the Double Folding Model (DFM) for the real part of the optical potential, is extended to heavy nuclei A 132 nuclei. The energy-dependent phenomenological imaginary part of the corresponding semi-microscopic optical model potential was obtained by taking into account also the dispersive correction to the DFM real potential, and used within a concurrent complete phenomenological analysis of the same data basis. Thus, a phenomenological optical potential was also obtained for the above-mentioned target-nuclei mass and energy ranges, while an ultimate assessment of ( , ), ( ,n) and ( ,p) reaction cross sections proves the suitable description of both the low energy elastic-scattering and -particle induced-reaction data
Study of Giant Pairing Vibrations with neutron-rich nuclei
We investigate the possible signature of the presence of giant pairing states
at excitation energy of about 10 MeV via two-particle transfer reactions
induced by neutron-rich weakly-bound projectiles. Performing particle-particle
RPA calculations on Pb and BCS+RPA calculations on Sn, we
obtain the pairing strength distribution for two particles addition and removal
modes. Estimates of two-particle transfer cross sections can be obtained in the
framework of the 'macroscopic model'. The weak-binding nature of the projectile
kinematically favours transitions to high-lying states. In the case of (~^6He,
\~^4He) reaction we predict a population of the Giant Pairing Vibration with
cross sections of the order of a millibarn, dominating over the mismatched
transition to the ground state.Comment: Talk presented in occasion of the VII School-Semina r on Heavy Ion
Physics hosted by the Flerov Laboratory (FLNR/JINR) Dubna, Russia from May 27
to June 2, 200
Structure of 10Be from the 12C 12C,14O 10Be reaction
The 12C 12C,14O two proton pick up reaction has been measured at 211.4 MeV incident energy to study the structure of states of 10Be up to excitation energies of 12 MeV. The measured partial angular distributions show pronounced oscillatory shapes, which were described by coupled reaction channels calculations. Spin parity assignments could be derived from these characteristic shapes and two definite assignments have been made. The state at 11.8 MeV has been identified as the 4 member of the ground state band, and the state at 10.55 MeV is assigned J pi 3 . At 5.96 MeV only the 1 1 member of the known 2 2 1 1 doublet is populated. The angular distribution of the peak at 9.50 MeV, which consists of several unresolved states, has been unfolded using contributions from known states at 9.56 MeV, 2 , and 9.27 MeV, 4 . The inclusion of a state at 9.4 MeV reported by Daito it et al. from the 10B t,3He 10Be reaction and tentatively assigned 3 improved the fit considerably. A K 2 band is formed with the 2 2 state as the band head and the 3 state as the second member. The structures of the K pi 0 1, 2 2, and 1 1 bands are discusse
Evidence of large nuclear deformation of S formed in Ne + C reaction
Deformations of hot composite S formed in the reaction Ne
( 7 -- 10 MeV/nucleon) + C have been estimated from the respective
inclusive -particle evaporation spectra. The estimated deformations for
S have been found to be much larger than the `normal' deformations
of hot, rotating composites at similar excitations. This further confirms the
formation of highly deformed long-lived configuration of Ne + C
at high excitations ( 70 -- 100 MeV) -- which was recently indicated from
the analysis of the complex fragment emission data for the same system.
Exclusive -particle evaporation spectra from the decay of hot composite
S also show similar behaviour.Comment: 9 pages, 6 figure
4He decay of excited states in 14C
A study of the 7Li(9Be,4He 10Be)2H reaction at E{beam}=70 MeV has been
performed using resonant particle spectroscopy techniques and provides the
first measurements of alpha-decaying states in 14C. Excited states are observed
at 14.7, 15.5, 16.4, 18.5, 19.8, 20.6, 21.4, 22.4 and 24.0 MeV. The
experimental technique was able to resolve decays to the various particle bound
states in 10Be, and provides evidence for the preferential decay of the high
energy excited states into states in 10Be at ~6 MeV. The decay processes are
used to indicate the possible cluster structure of the 14C excited states.Comment: accepted for publication in PR
Deformed two center shell model
A highly specialized two-center shell model has been developed accounting for
the splitting of a deformed parent nucleus into two ellipsoidaly deformed
fragments. The potential is based on deformed oscillator wells in direct
correspondance with the shape change of the nuclear system. For the first time
a potential responsible for the necking part between the fragments is
introduced on potential theory basis. As a direct consequence, spin-orbit {\bf
ls} and {\bf l} operators are calculated as shape dependent. Level scheme
evolution along the fission path for pairs of ellipsoidaly deformed fragments
is calculated. The Strutinsky method yields the shell corrections for different
mass asymmetries from the superheavy nucleus 122 and Cf all
along the splitting process.Comment: 32 pages, 8 figure
The population of deformed bands in Cr by emission of Be from the S + Mg reaction
Using particle- coincidences we have studied the population of final
states after the emission of 2 -particles and of Be in nuclei
formed in S+Mg reactions at an energy of . The data were obtained in a setup
consisting of the GASP -ray detection array and the multidetector array
ISIS. Particle identification is obtained from the E and E signals of
the ISIS silicon detector telescopes, the Be being identified by the
instantaneous pile up of the E and E pulses. -ray decays of the
Cr nucleus are identified with coincidences set on 2 -particles
and on Be. Some transitions of the side-band with show
stronger population for Be emission relative to that of 2
-particles (by a factor ). This observation is interpreted as
due to an enhanced emission of Be into a more deformed nucleus.
Calculations based on the extended Hauser-Feshbach compound decay formalism
confirm this observation quantitatively.Comment: 17 pages, 9 figures accepted for publication in J. Phys.
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