Publications (132)165.3 Total impact
-
Article: Isotopic Yield Distributions of Transfer- and Fusion-Induced Fission from 238U+12C Reactions in Inverse Kinematics
[show abstract] [hide abstract]
ABSTRACT: A novel method to access the complete identification in atomic number Z and mass A of fragments produced in low-energy fission of actinides is presented. This method, based on the use of multi- nucleon transfer and fusion reactions in inverse kinematics, is applied in this work to reactions between a 238U beam and a 12C target to produce and induce fission of moderately excited actinides. The fission fragments are detected and fully identified with the VAMOS spectrometer of GANIL, allowing the measurement of fragment yields of several hundreds of isotopes in a range between A ~ 80 and ~ 160, and from Z ~ 30 to ~ 64. For the first time, complete isotopic yield distributions of fragments from well-defined fissioning systems are available. Together with the precise measurement of the fragment emission angles and velocities, this technique gives further insight into the nuclear-fission process.04/2013; -
Article: Role of the cluster structure of 7Li in the dynamics of fragment capture
[show abstract] [hide abstract]
ABSTRACT: Exclusive measurements of prompt γ-rays from the heavy-residues with various light charged particles in the 7Li + 198Pt system, at an energy near the Coulomb barrier (E/Vb∼1.6) are reported. Recent dynamic classical trajectory calculations, constrained by the measured fusion, α- and t-capture cross-sections have been used to explain the excitation energy dependence of the residue cross-sections. These calculations distinctly illustrate a two-step process, breakup followed by fusion, in case of the capture of t and α clusters; whereas for 6He+p and 5He+d configurations, massive transfer is inferred to be the dominant mechanism. The present work clearly demonstrates the role played by the cluster structures of 7Li in understanding the reaction dynamics at energies around the Coulomb barrier.Physics Letters B 12/2012; · 3.95 Impact Factor -
Article: Isotopic fission fragment distributions as a deep probe to fusion-fission dynamics
[show abstract] [hide abstract]
ABSTRACT: During the fission process, the nucleus deforms and elongates up to the two fragments inception and their final separation at scission deformation. The evolution of the nucleus energy with deformation is determined by the macroscopic properties of the nucleus, and is also strongly influenced by the single-particle structure of the nucleus. The fission fragment distribution is a direct consequence of the deformation path the nucleus has encountered, and therefore is the most genuine experimental observation of the potential energy landscape of the deforming nucleus. Very asymmetric fusion-fission reactions at energy close to the Coulomb barrier, produce well-defined conditions of the compound nucleus formation, where processes such as quasi-fission, pre-equilibrium emission and incomplete fusion are negligible. In the same time, the excitation energy is sufficient to reduce significantly structural effects, and mostly the macroscopic part of the potential is responsible for the formation of the fission fragments. We use inverse kinematics combined with spectrometers to select and identify the fission fragments produced in $^{238}$U+$^{12}$C at a bombarding energy close to and well-above the Coulomb barrier. For the first time, the isotopic yields are measured over the complete atomic-number distribution, between Z=30 and Z=63. The experimental set-up also allows to identify transfer-induced reactions, which lead to low-energy fission where the nuclear shell structure shows a strong influence on the fission-fragment distributions. The resulting set of data gives the possibility to observe the fission fragment properties over a wide range of excitation energy, and they reveal the vanishing of the shell effects in the potential energy of the fissioning nucleus, as well as the influence of fission dynamics.09/2012; -
Article: Particle octupole-vibration coupling near 208Pb
[show abstract] [hide abstract]
ABSTRACT: High-spin states in nuclei around 208Pb were populated in deep inelastic collisions of 136Xe and 208Pb projectiles with 208Pb targets at beam energies about 12% above the Coulomb barrier. New states in nuclei in the vicinity of 208Pb have been found that result from the coupling of one and two quasi particles to the lowest 3− excitation of the 208Pb core. They show the influence of particle octupole-vibration coupling in a pronounced and clear way and verify the validity of this concept.European Physical Journal A 04/2012; 8(2):161-164. · 2.19 Impact Factor -
Article: Structure of light neutron-rich nuclei through coulomb dissociation
[show abstract] [hide abstract]
ABSTRACT: Coulomb breakup of neutron-rich nuclei around mass A ∼ 20 has been studied experimentally using secondary beams (∼ 500–600 MeV/u) of unstable nuclei produced at GSI. The spectroscopic factor deduced for the neutron occupying s 1/2 level in 15C ground state is consistent with the earlier reported value. The data analysis for Coulomb breakup of 17C shows that most of the cross section yields the 16C core in its excited state. For 17–22O, the low-lying E1 strength amounts up to about 12% of the energy weighted dipole sum rule strength depending on neutron excess. The cluster sum rule limit with 16O as a core is almost exhausted for 17,18O, while for more neutron rich isotopes the strength with respect to that limit decreases.Pramana 04/2012; 57(2):535-544. · 0.57 Impact Factor -
Article: Two-Particle Separation Energies in the Superdeformed Well
[show abstract] [hide abstract]
ABSTRACT: The location of nuclear closed shells, as evidenced through discontinuities in binding energy and one- and two-particle separation energy systematics, remains one of the simplest tests of global nuclear models. How shell gaps evolve, whether with increasing mass, increasing neutron:proton ratio or increasing deformation, is still uncertain, and it has recently been suggested that one must go beyond a static meanfield picture to include the effects of dynamic fluctuations in the nuclear shape even in the ground state. The identification of key properties which may distinguish between competing approaches is thus vital. Comparison of the binding energies of superdeformed nuclei in the A ≈ 190 region shows that two-proton separation energies are higher in the superdeformed state than in the normal state, despite the probably lower Coulomb barrier and lower total binding energy. Possible reasons for this difference are discussed. This somewhat counterintuitive result provides a critical test for global nuclear models.Journal of Physics Conference Series 09/2011; 312(9):092065. -
Article: Lifetime measurements in $^{63}$Co and $^{65}$Co
[show abstract] [hide abstract]
ABSTRACT: Lifetimes of the $9/2^-_1$ and $3/2^-_1$ states in $^{63}$Co and the $9/2^-_1$ state in $^{65}$Co were measured using the recoil distance Doppler shift and the differential decay curve methods. The nuclei were populated by multi-nucleon transfer reactions in inverse kinematics. Gamma rays were measured with the EXOGAM Ge array and the recoiling fragments were fully identified using the large-acceptance VAMOS spectrometer. The E2 transition probabilities from the $3/2^-_1$ and $9/2^-_1$ states to the $7/2^-$ ground state could be extracted in $^{63}$Co as well as an upper limit for the $9/2^-_1\rightarrow7/2^-_1$ $B$(E2) value in $^{65}$Co. The experimental results were compared to large-scale shell-model calculations in the $pf$ and $pfg_{9/2}$ model spaces, allowing to draw conclusions on the single-particle or collective nature of the various states.06/2011; -
Article: Pair and single neutron transfer with Borromean 8He
[show abstract] [hide abstract]
ABSTRACT: Direct observation of the survival of 199Au residues after 2n transfer in the system and the absence of the corresponding 67Cu in the system at various energies are reported. The measurements of the surprisingly large cross sections for 199Au, coupled with the integral cross sections for the various Au residues, is used to obtain the first model-independent lower limits on the ratio of 2n to 1n transfer cross sections from 8He to a heavy target. A comparison of the transfer cross sections for 6,8He on these targets highlights the differences in the interactions of these Borromean nuclei. These measurements for the most neutron-rich nuclei on different targets highlight the need to probe the reaction mechanism with various targets and represent an experimental advance towards understanding specific features of pairing in the dynamics of dilute nuclear systems.Physics Letters B 03/2011; · 3.95 Impact Factor -
Article: Publisher’s Note: Emergence of the N=16 shell gap in 21O
Physical Review C 01/2011; · 3.31 Impact Factor -
Article: Emergence of the N=16 shell gap in 21O
[show abstract] [hide abstract]
ABSTRACT: The spectroscopy of 21O has been investigated using a radioactive 20O beam and the (d,p) reaction in inverse kinematics. The ground and first excited states have been determined to be Jpi=5/2+ and Jpi=1/2+ respectively. Two neutron unbound states were observed at excitation energies of 4.76 +- 0.10 and 6.16 +- 0.11. The spectroscopic factor deduced for the lower of these interpreted as a 3/2+ level, reveals a rather pure 0d3/2 single-particle configuration. The large energy difference between the 3/2+ and 1/2+ states is indicative of the emergence of the N=16 magic number. For the higher lying resonance, which has a character consistent with a spin-parity assignment of 3/2+ or 7/2-, a 71% branching ratio to the first 2+ state in 20O has been observed. The results are compared with new shell model calculations.12/2010; -
Article: Migration of nuclear shell gaps studied in the d(24Ne,pγ)25Ne reaction.
[show abstract] [hide abstract]
ABSTRACT: The transfer of neutrons onto 24Ne has been measured using a reaccelerated radioactive beam of 24Ne to study the (d,p) reaction in inverse kinematics. The unusual raising of the first 3/2+ level in 25Ne and its significance in terms of the migration of the neutron magic number from N=20 to N=16 is put on a firm footing by confirmation of this state's identity. The raised 3/2+ level is observed simultaneously with the intruder negative parity 7/2- and 3/2- levels, providing evidence for the reduction in the N=20 gap. The coincident gamma-ray decays allowed the assignment of spins as well as the transferred orbital angular momentum. The excitation energy of the 3/2+ state shows that the established USD shell model breaks down well within the sd model space and requires a revised treatment of the proton-neutron monopole interaction.Physical Review Letters 05/2010; 104(19):192501. · 7.37 Impact Factor -
Article: Two-particle separation energy trends in the superdeformed well.
[show abstract] [hide abstract]
ABSTRACT: A measurement of the energy and spin of superdeformed states in 190Hg, obtained through the observation of transitions directly linking superdeformed and normal states, expands the number of isotopes in which binding energies at superdeformation are known. Comparison with neighboring nuclei shows that two-proton separation energies are higher in the superdeformed state than in the normal state, despite the lower Coulomb barrier and lower total binding energy. This unexpected result provides a critical test for nuclear models.Physical Review Letters 04/2010; 104(16):162501. · 7.37 Impact Factor -
Article: Migration of nuclear shell gaps studied in the d(24Ne,p gamma)25Ne reaction
[show abstract] [hide abstract]
ABSTRACT: The transfer of neutrons onto 24Ne has been measured using a reaccelerated radioactive beam of 24Ne to study the (d,p) reaction in inverse kinematics. The unusual raising of the first 3/2+ level in 25Ne and its significance in terms of the migration of the neutron magic number from N=20 to N=16 is put on a firm footing by confirmation of this state's identity. The raised 3/2+ level is observed simultaneously with the intruder negative parity 7/2- and 3/2- levels, providing evidence for the reduction in the N=20 gap. The coincident gamma-ray decays allowed the assignment of spins as well as the transferred orbital angular momentum. The excitation energy of the 3/2+ state shows that the established USD shell model breaks down well within the sd model space and requires a revised treatment of the proton-neutron monopole interaction. Comment: Phys. Rev. Lett. in press (4 pages, 3 figures)04/2010; -
Article: Minor actinide fission induced by multi-nucleon transfer reaction in inverse kinematics
[show abstract] [hide abstract]
ABSTRACT: In the framework of nuclear waste incineration and design of new generation nuclear reactors, experimental data on fission probabilities and on fission fragment yields of minor actinides are crucial to design prototypes. Transfer-induced fission has proven to be an efficient method to study fission probabilities of actinides which cannot be investigated with standard techniques due to their high radioactivity. We report on the preliminary results of an experiment performed at GANIL that investigates fission probabilities with multi-nucleon transfer reactions in inverse kinematics between a 238U beam on a 12C target. Actinides from U to Cm were produced with an excitation energy range from 0 to 30 MeV. In addition, inverse kinematics allowed to characterize the fission fragments in mass and charge. A key point of the analysis resides in the identification of the actinides produced in the different transfer channels. The new annular telescope SPIDER was used to tag the target-like recoil nucleus of the transfer reaction and to determine the excitation energy of the actinide. The fission probability for each transfer channel is accessible and the preliminary results for 238U are promising.EPJ Web of Conferences. 01/2010; -
Article: Neutron Transfer Studied with a Radioactive beam of 24Ne, using TIARA at SPIRAL
[show abstract] [hide abstract]
ABSTRACT: A general experimental technique for high resolution studies of nucleon transfer reactions using radioactive beams is briefly described, together with the first new physics results that have been obtained with the new TIARA array. These first results from TIARA are for the reaction 24Ne(d,p)25Ne, studied in inverse kinematics with a pure radioactive beam of 100,000 pps from the SPIRAL facility at GANIL. The reaction probes the energies of neutron orbitals relevant to very neutron rich nuclei in this mass region and the results highlight the emergence of the N=16 magic number for neutrons and the associated disappearance of the N=20 neutron magic number for the very neutron rich neon isotopes. Comment: Proceedings of the Carpathian Summer School of Physics, Mamaia-Constanta, Romania, 13-24 June 200512/2009; -
Article: Exploring fusion at extreme sub-barrier energies with weakly bound nuclei.
[show abstract] [hide abstract]
ABSTRACT: Results of measurement of residues formed in fusion of (6)Li with (198)Pt in the energy range of 0.68 < E/V(b) < 1.3 using a new sensitive off-beam technique are reported. The fusion excitation function and the derived average angular momenta do not indicate a change of slope at deep sub-barrier energies, contrary to recent observations. The present results for a system with weakly bound projectile confront the current understanding of the fusion hindrance at these low energies, underlying the role of internal reorganization on the dynamical path towards fusion.Physical Review Letters 12/2009; 103(23):232702. · 7.37 Impact Factor -
Article: Modern Rutherford experiment: tunneling of the most neutron-rich nucleus.
[show abstract] [hide abstract]
ABSTRACT: A modern variation of the Rutherford experiment to probe the tunneling of exotic nuclear matter from the measurement of the residues formed in the bombardment of (197)Au by extremely neutron-rich (8)He nuclei is presented. Using a novel off-beam technique the most precise and accurate measurements of fusion and neutron transfer involving reaccelerated unstable beams are reported. The results show unusual behavior of the tunneling of (8)He compared to that for lighter helium isotopes, highlighting the role of the intrinsic structure of composite many-body quantum systems and pairing correlations.Physical Review Letters 12/2009; 103(23):232701. · 7.37 Impact Factor -
Article: Absolute cross-sections from X–g coincidence measurements
[show abstract] [hide abstract]
ABSTRACT: An activation technique using coincidences between characteristic X-rays and g-rays to obtain absolute cross-sections is described. This method is particularly useful in the case of nuclei that decay by electron capture. In addition to the reduction of possible contamination, an improved detection sensitivity is achieved as compared to inclusive measurements, thereby allowing the extraction of absolute fusion cross-sections in the nano-barn range. Results of this technique for 6Li + 198Pt system, at energies around the Coulomb barrier are described. Future applications with low intensity radioactive ion beams are also discussed.Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 11/2008; 598:445. · 1.21 Impact Factor -
Article: Experimental study of resonance states in^{7} H and^{6} H
[show abstract] [hide abstract]
ABSTRACT: The 7H and 6H nuclear systems were investigated via transfer reactions with a 8He beam at 15.4A MeV impinging in a 12C target. The experimental setup allowed a complete reconstruction of the reaction kinematics with the MAYA gas detector, based on the active-target concept, where the carbon atoms of the filling isobutane played also the role of reaction target. The 7H resonance was observed at 0.57-0.21+0.42 MeV above the 3H+4n threshold with a width of 0.09-0.06+0.94 MeV. The 6H system was formed at 2.91-0.95+0.85 MeV with a resonance width of 1.52-0.35+1.77 MeV. These results show the availability of nuclear structure information well outside the bounding limits, resulting in an extraordinary input to improve the present models and understanding of nuclear matter.Phys. Rev. C. 10/2008; 78(4). -
Article: 1n and 2n transfer with the Borromean nucleus 6He near the Coulomb barrier.
[show abstract] [hide abstract]
ABSTRACT: Angular distributions for 1n and 2n transfer are reported for the 6He+65Cu system at E_{lab}=22.6 MeV. For the first time, triple coincidences between alpha particles, neutrons, and characteristic gamma rays from the targetlike residues were used to separate the contributions arising from 1n and 2n transfer. The differential cross sections for these channels, elastic scattering, and fusion were analyzed using a coupled reaction channels approach. The large measured ratio of the 2n-to-1n cross section and the strong influence of 2n transfer on other channels indicate that the dineutron configuration of 6He plays a dominant role in the reaction mechanism.Physical Review Letters 08/2008; 101(3):032701. · 7.37 Impact Factor
Top co-authors
Top Journals
Institutions
-
2011
-
Grand Accélérateur National d'Ions Lourds
Caen, Basse-Normandie, France
-
-
2010
-
University of Surrey
- Department of Physics
Guildford, ENG, United Kingdom
-
-
2003–2010
-
GANIL
Caen, Basse-Normandie, France
-
-
2009
-
Bhabha Atomic Research Centre
- Nuclear Physics Division
Mumbai, State of Maharashtra, India
-
-
2007
-
Universidad de Santiago de Compostela
- Departamento de Física de Partículas
Santiago de Compostela, Galicia, Spain
-
-
2001
-
University of Milan
Milano, Lombardy, Italy -
Goethe-Universität Frankfurt am Main
- Institut für Kernphysik
Frankfurt am Main, Hesse, Germany
-
-
1994–1998
-
University of Warsaw
- Institute of Experimental Physics
Warsaw, Masovian Voivodeship, Poland
-
