Quantum criticalities in a two-leg antiferromagnetic S=1/2 ladder induced by a staggered magnetic field

We study a two-leg antiferromagnetic spin-1/2 ladder in the presence of a staggered magnetic field. We consider two parameter regimes: strong (weak) coupling along the legs and weak (strong) coupling along the rungs. In both cases, the staggered field drives the Haldane spin-liquid phase of the ladder towards a Gaussian quantum criticality. In a generalized spin ladder with a non-Haldane, spontaneously dimerized phase, the staggered magnetic field induces an Ising quantum critical regime. In the vicinity of the critical lines, we derive low-energy effective field theories and use these descriptions to determine the dynamical response functions, the staggered spin susceptibility and the string order parameter.Comment: 29 pages of revtex, 10 figure

First g(2+) measurement on neutron-rich 72 Zn, and the high-velocity transient field technique for radioactive heavy-ion beams

The high-velocity transient-field (HVTF) technique was used to measure the g factor of the 2+ state of 72Zn produced as a radioactive beam. The transient-field strength was probed at high velocity in ferromagnetic iron and gadolinium hosts using 76Ge beams. The potential of the HVTF method is demonstrated and the difficulties that need to be overcome for a reliable use of the TF technique with high-Z, high-velocity radioactive beams are revealed. The polarization of K-shell vacancies at high velocity, which shows more than an order of magnitude difference between Z = 20 and Z = 30 is discussed. The g-factor measurement hints at the theoretically predicted transition in the structure of the Zn isotopes near N = 40

usion and breakup fusion of 6Li with 194Pt at energies around coulomb barrier

Results for fusion and breakup fusion reaction ( 6 Li+ 194 Pt) are presented and compared with other experimental data and model calculations. A strong isotopic effect is observed when comparing our data with results from ( 6 Li+ 198 Pt

Neutron-rich nuclei produced at zero degrees in damped collisions induced by a beam of 18O on a 238U target

Cross sections and corresponding momentum distributions have been measured for the first time at zero degrees for the exotic nuclei obtained from a beam of 18O at 8.5 MeV/A impinging on a 1 mg/cm2 238U target. Sizable cross sections were found for the production of exotic species arising from the neutron transfer and proton removal from the projectile. Comparisons of experimental results with calculations based on deep-inelastic reaction models, taking into account the particle evaporation process, indicate that zero degree is a scattering angle at which the differential reaction cross section for production of exotic nuclei is at its maximum. This result is important in view of the new generation of zero degrees spectrometers under construction, such as the S3 separator at GANIL, for example

2n-Evaporation Channel In The

Excitation functions of the reaction products were measured for the reactions induced by 4,6He projectiles on 208,206Pb targets, leading to the same compound nucleus. The excitation functions for the 2n evaporation channels were obtained at energies below the sub-Coulomb barrier region. A large value of the fusion cross section was observed in the case of the reaction induced by the weakly bound 6He projectile. This reflects an unusual mechanism is present in reactions induced by weakly bound nuclei

Status of the caviar detector at LISE-GANIL

Spectromètre LISEInternational audienceIPhysics that motivated the building of the LISE magnetic spectrometer, main ideas exposed in the scientific council of GANIL June 4th 1981 by M. Brian and M. Fleury, were: atomic physics studies with stripped ions and the study of new isotopes produced by the fragmentation of beams. The LISE line is a doubly-achromatic spectrometer (angle and position), with a resolution better than 10-3. Since the first experiment performed in 1984, several improvements of the spectrometer were made: use of an achromatic degrader (1987, used for the first time in the world), building of the achromatic deviation and the Wien Filter (1990), building of a new selection dipole and associated vertical platform (1994), building of the new LISE2000 line (2001), use of the Caviar detector (2002), building of the CLIM target (2007). Despite an extreme international competition, the LISE spectrometer remains a world-leader equipment using more than 50 % and up to 90 % of the beam time available at GANIL. This paper presents the status of CAVIAR detector which consist of a MPWC dedicated to in flight particle position at the first dispersive plane of LISE. Since two years, intensive efforts were done with the objective to propose a 'plug and play' detector for nuclear physic experiments. We will describe the motivations and the system from MPWC up to the acquisition system. As example few experimental results will be presented

Study of fission reactions induced by

Study of fission reactions induced by 4,6He and 7Li beams on 209Bi and 208Pb targets, leading to the production of 210,212A compound nuclei, was performed. It was shown that the fission excitation functions for the three reactions 4,6He + 209Bi and 7Li + 208Pb had similar behavior within the experimental error for a broad range of energy. More likely, halo structure of 6He is not reflected on the fission reaction mechanism. Otherwise, a large value of the fusion cross section was observed so far, as it could be expected in the case of weakly bound character of 6He projectile