63 research outputs found
Investigation of the 6He cluster structures
The 4He+2n and t+t clustering of the 6He ground state were investigated by
means of the transfer reaction 6He(p,t)4He at 25 MeV/nucleon. The experiment
was performed in inverse kinematics at GANIL with the SPEG spectrometer coupled
to the MUST array. Experimental data for the transfer reaction were analyzed by
a DWBA calculation including the two neutrons and the triton transfer. The
couplings to the 6He --> 4He + 2n breakup channels were taken into account with
a polarization potential deduced from a coupled-discretized-continuum channels
analysis of the 6He+1H elastic scattering measured at the same time. The
influence on the calculations of the 4He+t exit potential and of the triton
sequential transfer is discussed. The final calculation gives a spectroscopic
factor close to one for the 4He+2n configuration as expected. The spectroscopic
factor obtained for the t+t configuration is much smaller than the theoretical
predictions.Comment: 10 pages, 11 figures, accepted in PR
Asymmetry to symmetry transition of Fano line-shape: Analytical derivation
An analytical derivation of Fano line-shape asymmetry ratio has been
presented here for a general case. It is shown that Fano line-shape becomes
less asymmetric as \q is increased and finally becomes completely symmetric in
the limiting condition of q equal to infinity. Asymmetry ratios of Fano
line-shapes have been calculated and are found to be in good consonance with
the reported expressions for asymmetry ratio as a function of Fano parameter.
Application of this derivation is also mentioned for explanation of asymmetry
to symmetry transition of Fano line-shape in quantum confined silicon
nanostructures.Comment: 3 figures, Latex files, Theoretica
Structure of low-lying states of C from proton elastic and inelastic scattering
NESTER PTH, expérience GANIL, équipement SISSITo probe the ground state and transition densities, elastic and inelastic scattering on a proton target were measured in inverse kinematics for the unstable C and C nuclei at 45.3 and 40.6 MeV/nucleon, respectively. The detection of the recoil proton was performed by the MUST telescope array, in coincidence with a wall of scintillators for the quasiprojectile. The differential cross sections for elastic and inelastic scattering to the first excited states are compared to the optical model calculations performed within the framework of the microscopic nucleon-nucleus Jeukenne-Lejeune-Mahaux potential. Elastic scattering is sensitive to the matter-root-mean square radius found to be 2.420.1 and 2.330.1 fm, for C, respectively. The transition densities from cluster and mean-field models are tested, and the cluster model predicts the correct order of magnitude of cross sections for the transitions of both isotopes. Using the Bohr-Mottelson prescription, a profile for the C transition density from the ground to the state is deduced from the data. The corresponding neutron transition matrix element is extracted: Mn=5.511.09 fm
Large enhancement of the sub-barrier fusion probability for a halo nucleus
The fusion-fission cross sections of the He-4 + U-238 and He-6 + U-238 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 He-6 data show a regular trend with a large enhancement below the barrier which is attributed to the halo structure of the He-6 nucleus
PlioâQuaternary exhumation history of the central Nepalese Himalaya: 2. Thermokinematic and thermochronometer age prediction model
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95647/1/tect1875.pd
Structure of light exotic nuclei He and C from (p,p') reactions
NESTERThe structure of the light unstable nuclei 10,11C and 6,8He is investigated by means of (p,pâČ) reactions. The experiments were performed at GANIL using the MUST detector, an array of Si and SiLi telescopes. The (p,pâČ) are analyzed within the framework of the microscopic JLM potential, allowing to test the densities predicted by structure models. Preliminary data from the 8He(p,oâČ) reaction performed at the SPIRAL facility at 15.6 MeV/nucleon are discussed
Distribution of the Late-Quaternary deformation in Northwestern Himalaya
International audienceThree main Cenozoic thrusts at the front of Northwestern Himalaya have accommodated most of the IndiaâEurasia convergence across the belt over the last million years and produced the present relief. Their recent tectonic activity is poorly known because of the long period of inaccessibility of the Jammu and Kashmir state, and because the latest and only large earthquake recorded in the region occurred in 1555 AD. We show where the deformation is localized during the Late-Quaternary, and determine shortening rates across the structures by analyzing the geometry and chronology of geomorphic markers. The Main Boundary Thrust in this region ceased moving at least âŒ30 ka ago. On the contrary, the more external MedlicottâWadia Thrust and Main Frontal Thrust, both merging at depth on the sub-flat detachment of the Main Himalayan Thrust, exhibit hectometric-scale deformations accumulated during the last thousands of years. The total shortening rate absorbed by these faults over the last 14â24 ka is between 13.2 and 27.2 mm/yr ( and , respectively). Part of this deformation may be associated to the geometry of the Chenab reentrant, which could generate an extra oblique component. However, the lower bound of our shortening rates is consistent with previously determined geodetic rates. Active deformation on these structures follows an in-sequence/out-of-sequence pattern, with breaking of both ramps being possible for earthquakes triggered on the main detachment
A complex thrust sequence in western Himalaya: the active Medlicott Wadia Thrust.
15 pagesInternational audienceThe recent activity of the Medlicott-Wadia Thrust (MWT) is investigated by geomorphic and tectonic studies in the Riasi zone, south of the Pir Panjal range (India, Jammu-Kasmir state of western Himalaya). In the Riasi area, the MWT forms a splay of five faults that dip northward. The recent activity of the splay is quantified using a set of deformed Quaternary alluvial units. The central branch of the thrust splay moved Precambrian limestones above Quaternary sediments and is sealed by 36 ± 3 ka (youngest OSL age) deposits. The other branches offset the top of a 15 ± 1 ka (youngest OSL age) alluvial fan by 180 to 120 m; the two southernmost branches form 17â34 m high non-cylindrical scarps and the two northernmost branches also offset the fan by âŒ8 m and âŒ54 m, respectively. A balanced cross-section parallel to the N210°E thrust motion suggests that the sequence of activity is complex: an in-sequence propagation is found for the three southern Tea, Scorpion and Rain faults and an out-of-sequence reactivation for the northern Pillar fault. Furthermore, several thrusts simultaneously activated for intervals of a few thousand years, whereas others are episodically inactive. Nearly 10 mm/yr of India-Eurasia convergence is regularly absorbed by the MWT, a value greater than the one estimated for the western segment of the MWT affected by the 2005 Kashmir earthquake, where the thrust tectonics interacts with the complex kinematics of the syntax. This work indicates that the MWT is very active and might be related to thick-skinned tectonics in the western Himalaya
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