579 research outputs found
Collective excitations in the superdeformed well
No full textCollective excitations are commonplace features in nuclei at normal deformation. It has been suggested that both in the A\sim 190 and 150 superdeformed (SD) nuclei, collective vibrational states might occur in the same excitation energy range as quasi-particle and single-particle excitations. In particular, the large deformation associated with SD nuclei brings together orbitals from many spherical shells and leads to the close proximity of states with opposite parity, favouring octupole shape vibrations. However, to date, \sim 200 SD bands have been reported in more than 50 nuclei and in most cases, the excited SD bands have been interpreted as single or quasi-particle excitations. Only in very few cases, has the collective excitation scenario been suggested. Where are the collective states in SD nuclei? The question is particularly relevant in even--even A=190 nuclei in which SD states are observed at lower rotational frequency and hence the additional influence of the pair gap makes the collective excitations more competitive with quasi-particle excitations.F. Hannachi, A. Korichi, A.N. Wilson, A. Lopez-Martens, M. Rejmund, C. Schueck, Ch. Vieu, G. Chmel, A. Goergen, H. Huebel, D. Rossbach, S. Schoenwasser, M. Bergstroem, B.M. Nyako, J. Timar, D. Bazzacco, S. Lunardi, C. Rossi-Alvarez, P. Bednarczyk, N. Kintz, S. Naguleswaran, A. Astier, D.M. Cullen, J.F. Sharpey-Schafer, T. Lauritsen, R. Wadsworthhttp://th-www.if.uj.edu.pl/acta/vol32/abs/v32p1083.ht
Linear polarization measurement of interband transitions in superdeformed (190)Hg: model-independent evidence for octupole vibrational structures
No full textThe linear polarization of γ rays between excited and yrast superdeformed (SD) states in 190Hg was measured using the four-element CLOVER detectors of the EUROBALL IV γ-ray spectrometer. This measurement shows in a model-independent way that the interband transitions which compete with the highly collective in-band quadrupole transitions are largely enhanced electric dipoles. Not only do these results represent the first measurement of the multipolarity of transitions between different SD states, but they also provide strong evidence for the interpretation of the structures in the SD minimum of the A∼190 region in terms of octupole excitations.A. Korichi, A. N. Wilson, F. Hannachi, A. Lopez-Martens, M. Rejmund, C. Schück, Ch. Vieu, G. Chmel, A. Görgen, H. Hübel, D. Rossbach, S. Schönwasser, M. Bergström, B. M. Nyakó, J. Timár, D. Bazzacco, S. Lunardi, C. Rossi-Alvarez, P. Bednarczyk, N. Kintz, S. Naguleswaran, A. Astier, D. M. Cullen, J. F. Sharpey-Schafer, T. Lauritsen, and R. Wadswort
Fusion-Fission of superheavy compound nuclei produced in reacions with heavy ions beyond Ca
No full textTotal Kinetic Energy - Mass distributions of fission-like fragments for the reactions of 22Ne, 26Mg, 36S, 48Ca, 58Fe and 64Ni ions with actinides leading to the formation of superheavy compound systems with Z=108-120 at energies near the Coulomb barrier have been measured. Fusion-fission cross sections were estimated from the analysis of mass and total kinetic energy distributions. It was found that the fusion probability drops by three orders of magnitude for the formation of the compound nucleus with Z=120 obtained in the reaction 64Ni+238U compared to the formation of the compound nucleus with Z=112 obtained in the reaction 48Ca+238U at the excitation energy of the compound nucleus of about 45 MeV. From our analysis it turns out that the reaction 64Ni+238U is not suitable for the synthesis of element Z=120
Pair transfer processes probed at deep sub barrier energies
No full textMultinucleon transfer cross sections in the system Ca-40+Zr-96 have been measured at bombarding energies ranging from the Coulomb barrier to similar to 25% below. Target-like (lighter) recoils in inverse kinematics have been completely identified in A,Z and Q-value with the large solid angle magnetic spectrometer PRISMA. The experimental slopes of the neutron transfer probabilities at large internuclear separation are consistent with the values derived from the binding energies. A phenomenological interpretation of the transfer probabilities indicates the presence of enhanced values for the even number of neutron transfers
Reactions induced by 11Be beam at Rex-Isolde
No full textThe collision induced by the three Beryllium isotopes, 9,10,11Be, on a 64Zn target were investigated at Ec.m. ≈ 1.4 the Coulomb barrier. The experiments with the radioactive 10,11Be beams were performed at the Rex-Isolde facility at CERN. In the case of 9,10Be, elastic scattering angular distributions were measured whereas, in the 11Be case, the quasielastic scattering angular distribution was obtained. A strong damping of the quasielastic cross-section was observed in the 11Be case, in the angular range around the Coulomb-nuclear interference peak. In this latter case a large total-reaction cross-section is found. Such a cross-section is more than a factor of two larger than the ones extracted in the reactions induced by the non-halo Beryllium isotopes. A large contribution to the total-reaction cross-section in the 11Be case could be attributed to transfer and/or break-up events
Fusion of 60Ni + 100Mo below barrier
No full textThe fusion cross section of 60Ni + 100Mo has been measured down to microbarn level, looking for hindrance at low energy, in a system with positive Q-values for neutron transfer. The measured cross sections look similar to those of the nearby 64Ni + 100Mo, but no conclusive statement can be made at this stage, as to the onset of hindrance in this system
Gamma spectroscopy of isotopically identified neutron-rich fission fragments
No full textInternational audienc
Neutron Rich Fission fragments
No full textResearch Programme at GANIL-SPIRAL1-SPIRAL2 and Related Instrumentation -
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