The present work provides a literature survey of elastic scattering of exotic nuclei from
6He to
17F. It presents a set of definitions that allow different analyses to be put into a common language. ...A calculational approach is proposed that yields consistent results across different beams and targets so that conclusions concerning the influence of virtual and real breakup as well as transfer couplings on the elastic scattering may be drawn. Calculations of elastic scattering around the Coulomb barrier are emphasised, employing a Pb target whose large
Z
allows the interplay between nuclear and Coulomb forces to be exploited to maximise possible effects arising from proton or neutron haloes or skins. A series of test calculations is performed and where possible compared to data, demonstrating that there are instances where coupling to transfer channels can have a large effect on the elastic scattering angular distributions. By careful choice of target/beam combination, different aspects of the coupling effects may be emphasised.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The present understanding of reaction processes involving light unstable nuclei at energies around the Coulomb barrier is reviewed. The effect of coupling to direct reaction channels on elastic ...scattering and fusion is investigated, with the focus on halo nuclei, for which such effects are expected to be most important. With the aim of resolving possible ambiguities in the terminology a short list of definitions for the relevant processes and quantities is proposed. This is followed by a review of the experimental and theoretical tools and information presently available. The effect of breakup couplings on elastic scattering and of transfer couplings on fusion is investigated with a series of model calculations within the coupled-channels framework. The experimental data on fusion are then compared to ‘bare’ no-coupling one-dimensional barrier penetration model calculations employing reasonably realistic double-folded potentials. On the basis of these model calculations and comparisons with experimental data, conclusions are drawn from the observation of recurring features. The total fusion cross-sections for halo nuclei show a suppression with respect to the ‘bare’ calculations at energies just above the barrier that is probably due to single neutron transfer reactions. The data for total fusion are also consistent with a possible sub-barrier enhancement; however, this observation is not conclusive and other couplings besides the single-neutron channels would be needed in order to explain any actual enhancement. We find that a characteristic feature of halo nuclei is the dominance of direct reactions over fusion at near and sub-barrier energies; the main part of the cross-section is related to neutron transfers, while calculations indicate only a modest contribution from the breakup process.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The low-lying spectroscopy of 6He was investigated via the 2-neutron transfer reaction p (He 8 , t) with the 8He beam delivered by the SPIRAL facility at 15.4 A MeV . The light charged particles ...produced by the direct reactions were measured using the MUST2 Si-strip telescope array. Above the known 2 + state, two new resonances were observed: at E a = 2.6 +/- 0.3 MeV (width Phi = 1.6 +/- 0.4 MeV) and at 5.3 +/- 0.3 MeV with Phi = 2 +/- 1 MeV . Through the analysis of the angular distributions, they correspond to a 2 + state and to an L = 1 state, respectively. These new states, challenging the nuclear theories, could be used as benchmarks for checking the microscopic inputs of the newly improved structure models, and should trigger development of models including the treatments of both core excitation and continuum coupling effects.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Elastic scattering and breakup angular distribution measurements for the systems
6,7
Li + p were performed at the MAGNEX facility of the
I
stituto
N
azionale di
F
isica
N
ucleare-
L
aboratori
N
...azionali del
S
ud (INFN-LNS) in Catania, in the energy range of (2.3–5.4)AMeV. The breakup channel was identified and quantified adopting the algorithm MULTIP.Within this algorithm which is a Monte Carlo simulation code, the history of the breakup fragments can be tagged from the rest frame of the decay nucleus itself to the laboratory frame. Angular distribution data of both elastic scattering and breakup were analyzed under the same theoretical model and the influence of continuum on the elastic channel was investigated.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The fusion-fission cross sections of the 4He+238U and 6He+238U systems have been measured, at Louvain-la-Neuve, for energies around and below the Coulomb barrier, using an array of Si detectors ...surrounding a UF4 target. The data taken with 4He are in good agreement with previous data and with the coupled channel fusion calculation performed with ECIS. The 6He data show a regular trend with a large enhancement below the barrier which is attributed to the halo structure of the 6He nucleus.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
The spectroscopy of 27Ne has been investigated through the one-neutron transfer reaction 26Ne(d,p)27Ne in inverse kinematics at 9.7 MeV/nucleon. The results strongly support the existence of a ...low-lying negative parity state in 27Ne, which is a signature of a reduced sd–fp shell gap in the N=16 neutron-rich region, at variance with stable nuclei.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Elastic scattering angular distributions for systems with reduced mass between 3 and 34 and energies varying between 25 and 120 MeV/nucleon were analyzed. The stable
4He, its exotic partner
6He, and ...the weakly bound
6,7Li nuclei were included as projectiles in the systematics. Optical model data analyzes were performed with an adjustable factor of normalization included in the imaginary part of the potential. These analyzes indicated a reduction of absorption for systems with small reduced masses that was detected due to the refractive nature of the scattering by light systems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Proton elastic and inelastic scattering angular distributions to the 2
+
1 and the 3
−
1 states for the neutron-rich nucleus
20
O were measured with a secondary beam using the MUST silicon strip ...detector array. Data for
18
O were also obtained for comparison. A phenomenological analysis has been used to deduce the deformation parameters
β
p,p′ for the collective excitations. Matter and transition densities were generated from self-consistent QRPA calculations. DWBA calculations using microscopic optical potentials obtained with these densities and the JLM interaction are compared to the data. The isovector character of the 2
+
1 state in
20
O is confirmed and predictions are discussed for the properties of the heavier neutron-rich oxygen isotopes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A beam detector system, CATS (Chambre A Trajectoires de Saclay), was designed to provide event-by-event particle tracking in experiments with radioactive beams at GANIL. It consists of two low ...pressure multiwire proportionnal chambers with one plane of anode wires placed between two cathode planes (active area: 70×70
mm
2), respectively segmented into 28 vertical or horizontal strips (2.54
mm wide). The anode wires deliver a time signal allowing a time of flight measurement with an accuracy between 440
ps and 1.2
ns, depending on the energy loss of incident particles in the detector. The cathode strips are individually read out and the position of incoming particles is reconstructed using a charge centroid finding algorithm. A spatial resolution of 400
μm (700
μm) was achieved during in beam experiment, with a counting rate of 1.5×10
5 (10
6) particles per second.
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IJS, IMTLJ, KILJ, KISLJ, NUK, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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