644 research outputs found
Three-centre cluster structure in 11C and 11B
Studies of the 16O(9Be,alpha 7Be)14C, 7Li(9Be,alpha 7Li)5He and 7Li(9Be,alpha
alpha t)5He reactions at E(beam)=70 and 55 MeV have been performed using
resonant particle spectroscopy techniques. The 11C excited states decaying into
alpha+7Be(gs) are observed between 8.5 and 13.5 MeV. The alpha+7Li(gs),
alpha+7Li*(4.652 MeV) and t+8Be(gs) decays of 11B excited states between 9 and
19 MeV are observed. The decay processes are used to indicate the possible
three-centre 2alpha+3He (2alpha+3H) cluster structure of observed states. This
cluster structure is more prominent in the positive-parity states, where two
rotational bands with large deformations are suggested. Excitations of some of
the observed T=1/2 resonances coincide with the energies of previously measured
T=3/2 isobaric analogs of the 11Be states,indicating that these states may have
mixed isospin.Comment: Contribution for the proceedings of the NUSTAR'05: NUclear STructure,
Astrophysics and Reactions, University of Surrey, Guildford, UK; accepted for
publication in Journal of Physics
Binary reaction decays from 24Mg+12C
Charged particle and gamma decays in 24Mg* are investigated for excitation
energies where quasimolecular resonances appear in 12C+12C collisions. Various
theoretical predictions for the occurence of superdeformed and hyperdeformed
bands associated with resonance structures with low spin are discussed within
the measured 24Mg* excitation energy region. The inverse kinematics reaction
24Mg+12C is studied at E_lab(24Mg) = 130 MeV, an energy which enables the
population of 24Mg states decaying into 12C+12C resonant break-up states.
Exclusive data were collected with the Binary Reaction Spectrometer in
coincidence with EUROBALL IV installed at the VIVITRON Tandem facility at
Strasbourg. Specific structures with large deformation were selectively
populated in binary reactions and their associated gamma decays studied.
Coincident events associated with inelastic and alpha-transfer channels have
been selected by choosing the excitation energy or the entry point via the
two-body Q-values. The analysis of the binary reaction channels is presented
with a particular emphasis on 24Mg-gamma, 20Ne-gamma and 16O-gamma
coincidences. New information (spin and branching ratios) is deduced on
high-energy states in 24Mg and 16O, respectively.Comment: 27 pages, 8 figures, 1 tabl
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
Emergence of the N=16 shell gap in 21O
The spectroscopy of O21 has been investigated using a radioactive O20 beam and the (d,p) reaction in inverse kinematics. The ground and first excited states have been determined to be Jπ=5/2+ and 1/2+, respectively. Two neutron unbound states were observed at excitation energies of 4.77(10) and 6.17(11) MeV. The spectroscopic factor deduced for the lower of these, interpreted as a 3/2+ level, reveals a relatively pure (60%) 0d3/2 single-particle configuration, in good agreement with shell-model calculations that predict O26 to be unbound. The large energy difference between the 3/2+ and 1/2+ states is indicative of the emergence of the N=16 shell gap, which is estimated to be 5.1(11) MeV. For the higher-lying resonance, which has a character consistent with a spin-parity assignment of 3/2+ or 7/2-, a 0.71(22) branching ratio to the first 2+ state in O20 has been observed.Unión Europea EURISOL 515768 RIDSNSF PHY-075809
Reaction mechanisms in 24Mg+12C and 32S+24Mg
The occurence of "exotic" shapes in light N=Z alpha-like nuclei is
investigated for 24Mg+12C and 32S+24Mg. Various approaches of superdeformed and
hyperdeformed bands associated with quasimolecular resonant structures with low
spin are presented. For both reactions, exclusive data were collected with the
Binary Reaction Spectrometer in coincidence with EUROBALL IV installed at the
VIVITRON Tandem facility of Strasbourg. Specific structures with large
deformation were selectively populated in binary reactions and their associated
-decays studied. The analysis of the binary and ternary reaction
channels is discussed.Comment: 7 pages, 4 figures, Paper presented at the Fusion08 International
Conference on New Aspects of Heavy Ion Collisions Near the Coulomb Barrier,
Chicago. Proceedings to be published by AIP Conference Proceedings Illinois,
USA, September 22-26, 200
Structure of 12Be: intruder d-wave strength at N=8
The breaking of the N=8 shell-model magic number in the 12Be ground state has
been determined to include significant occupancy of the intruder d-wave
orbital. This is in marked contrast with all other N=8 isotones, both more and
less exotic than 12Be. The occupancies of the 0 hbar omega neutron p1/2-orbital
and the 1 hbar omega, neutron d5/2 intruder orbital were deduced from a
measurement of neutron removal from a high-energy 12Be beam leading to bound
and unbound states in 11Be.Comment: 5 pages, 2 figure
Clusters in Light Nuclei
A great deal of research work has been undertaken in the alpha-clustering
study since the pioneering discovery, half a century ago, of 12C+12C molecular
resonances. Our knowledge of the field of the 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. In this work, the occurence of "exotic"
shapes in light N=Z alpha-like nuclei is investigated. Various approaches of
superdeformed and hyperdeformed bands associated with quasimolecular resonant
structures are presented. Results on clustering aspects are also discussed for
light neutron-rich Oxygen isotopes.Comment: 12 pages, 5 figures. Invited Talk presented by C. Beck at the
Zakopane Conference on Nuclear Physics "Extremes of the Nuclear Landscape"
XLV in the series of Zakopane Schools of Physics - International Symposium -
Zakopane, Poland, August 30 - September 5, 2010.To be publihed in Acta
Physica Polonica B42 no 3, March 201
Structure of Be probed via secondary beam reactions
The low-lying level structure of the unbound neutron-rich nucleus Be
has been investigated via breakup on a carbon target of secondary beams of
B at 35 MeV/nucleon. The coincident detection of the beam velocity
Be fragments and neutrons permitted the invariant mass of the
Be+ and Be++ systems to be reconstructed. In the case of
the breakup of B, a very narrow structure at threshold was observed in
the Be+ channel. Contrary to earlier stable beam fragmentation
studies which identified this as a strongly interacting -wave virtual state
in Be, analysis here of the Be++ events demonstrated that
this was an artifact resulting from the sequential-decay of the
Be(2) state. Single-proton removal from B was found to
populate a broad low-lying structure some 0.70 MeV above the neutron-decay
threshold in addition to a less prominent feature at around 2.4 MeV. Based on
the selectivity of the reaction and a comparison with (0-3)
shell-model calculations, the low-lying structure is concluded to most probably
arise from closely spaced J=1/2 and 5/2 resonances
(E=0.400.03 and 0.85 MeV), whilst the broad
higher-lying feature is a second 5/2 level (E=2.350.14 MeV). Taken
in conjunction with earlier studies, it would appear that the lowest 1/2
and 1/2 levels lie relatively close together below 1 MeV.Comment: 14 pages, 13 figures, 2 tables. Accepted for publication in Physical
Review
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