J.M. Casandjian

Proton elastic scattering on light neutron-rich nuclei

Abstract Proton-nucleus elastic scattering angular distributions have been measured for 6 He, 7 Li, 10 Be, 11 Be secondary beams. These data, together with other elastic scattering data for proton on unstable nuclei, have been analyzed using phenomenological and microscopic optical model approaches. To reproduce the experimental angular distributions for unstable nuclei, it was necessary to renormalize either the real or imaginary part of the optical potential. The influence of the break-up channels on the results is discussed.

A fast position sensitive microchannel plate detector for ray-tracing of charged particles

Abstract Studies of nuclear reactions by the use of secondary beams involve the need of ray-tracing of either the incident beam or the reaction products. For high resolution experiments, the material interposed to the trajectory of particles must be very thin, in order to produce a minimum of perturbation of their characteristics. Secondary electrons emitted from thin foils are well suited for fast position determination. A microchannel plate detector has been developed in order to accomplish the tracing of these electrons. A parallel E - and B -field configuration, applied as a focusing device for the emitted electrons, produces an image of a reaction vertex. Thus an image of the trajectory of particles can be obtained by placing the electron producing foil into the beamline and record the position of the accelerated and focused electrons hitting a grid of sensewires.

Coupling effects in the elastic scattering of the exotic nucleus 6He on protons

Abstract Cross sections for the elastic scattering of 6He radioactive nuclear beam on proton targets have been measured at 38.3 MeV/nucleon. With a view to test the ability of general optical potentials to reproduce the data for scattering of unstable nuclei, the present results, as well as other existing data for 6,8He, have been analyzed within the framework of the microscopic Jeukenne–Lejeune–Mahaux nucleon–nucleus potential. The angular distributions were found to be best reproduced by reducing the real part of the optical potential. This renormalization can be seen as a consequence of the complex polarization potential produced by the coupling to the continuum due to the weakly bound nature of the unstable nuclei. This effect can be simulated in a phenomenological analysis by a surface potential.

Elastic scattering of 6He and its analysis within a four-body eikonal model

Abstract We have measured the elastic scattering of a 6 He secondary beam on a 12 C target at 41.6 MeV/u. The secondary beam was produced by fragmentation with SISSI, and transported to SPEG. The combined use of SISSI and SPEG allows very good quality data to be obtained in terms of energy and angular resolution. The cross section is analysed within a 4-body (α+n+n+ 12 C) eikonal scattering model which is completely parameter-free. Very good agreement with the data is found.

Search for the signature of a halo structure in the p(6He, 6Li)n reaction

Abstract The elastic scattering p( 6 He, 6 He)p and charge exchange reaction p( 6 He, 6 Li)n have been measured in reverse kinematics with a secondary 6 He beam. The angular distributions for these reactions were obtained. In the case of the charge exchange reaction, the ratio of the cross section for the Gamow-Teller transition to the ground state, and for the Fermi transition to the isobaric analog state is a measure of the relative strength of the two components of the exchange interaction, V στ and V τ . This ratio is found to be compatible with existing systematics for stable T = 1 nuclei, and no clear signature of a halo structure was found in the present data.

A cyclotron as a high resolution mass spectrometer for fast secondary ions

Abstract We present the first results from a new method for mass measurements developed using the GANIL coupled cyclotrons, which uses a cyclotron as a high resolution mass spectrometer for fast secondary ions. We report here the results obtained with primary beams of 13.74 MeV/nucleon 15N and 12C, accelerated by the first cyclotron and incident on a Ta target located between the cyclotrons. Reaction products with mass-to-charge ratio of 3 were selected and accelerated by the second cyclotron. The accelerated secondary nuclei were detected in the interior of the second cyclotron using a plastic scintillator located on a radially moving rod. Details of the procedure and results are discussed. When two masses are close enough to be accelerated simultaneously by the second cyclotron, the precision in the measurement of the mass difference is better than 10−6.

Nuclear spin alignment and static moments of light projectile fragments measured with the Level Mixing Resonance (LMR) method

Abstract We report on the first Level Mixing Resonance experiments performed on β-decaying nuclei produced and aligned in intermediate energy fragmentation reactions. From the resonant change of the β-asymmetry as a function of a static magnetic field, we derived information on the initial alignment of 12B and 18N projectile fragments and on the nuclear structure of the neutron 18N nucleus. Positive alignments ranging from 0.9% to 14.4% have been found for different cuts in the longitudinal momentum distribution of 12B and 18N fragments. A very large ratio for the quadrupole frequency to the magnetic moment has been measured for the neutron rich 18N fragments.

CHARGE-EXCHANGE REACTION INDUCED BY 6HE AND NUCLEAR DENSITIES

Abstract The charge-exchange reaction p( 6 He, 6 Li)n is studied in reverse kinematics with a secondary 6 He beam at 41.6 MeV/nucleon. The transition connecting the ground state of 6 He to its isobaric analog state in 6 Li has been measured and analyzed in the context of a microscopic calculation. The angular distribution is shown to be sensitive to the nuclear interaction potential and to the radii of the density distribution of 6 He. It is shown that only a coherent microscopic analysis may disentangle the different contributions.

Elastic scattering and charge exchange reaction with light neutron rich exotic beams

Abstract The elastic scattering of 6 He, 10,11 Be secondary beams on a (CH 2 ) 3 target and the charge exchange reaction p( 6 He, 6 Li)n have been measured. A microscopic optical potential was used to reproduce the proton-nucleus elastic scattering data. No clear signature of a halo structure was found in the present data for the elastic scattering and charge exchange reaction, due to the lack of large angle measurement.

Mass measurements near N=Z

Abstract After an outline of the physics motivations, that illustrate why we think it is important to measure masses in the region N≈Z, we report on on experiments performed at Ganil. An experiment aimed at measuring the masses of proton-rich nuclei in the mass region A ≈ 60–80 has been performed, using a direct time-of-flight technique in conjunction with SISSI and the SPEG spectrometer at GANIL. The nuclei were produced via the fragmentation of a 78 Kr beam (73 meV/nucleon). A novel technique for the purification of the secondary beams, based on the stripping of the ions and using the α and the SPEG spectrometers, was succesfully checked. It allows for good selectivity without altering the beam quality. Secondary ions of 100 Ag, 100 Cd, 100 In and 100 Sn were produced via the fusion-evaporation reaction 50 Cr + 58 Ni at an energy of 5.1 MeV/nucleon, and were accelerated simultaneously in the second cyclotron of GANIL (CSS2). About 10 counts were observed from the production and acceleration of 100 Sn 22+ . The masses of 100 Cd, 100 In and 100 Sn were measured with respect to 100 Ag using the CSS2 cyclotron, with precisions of 2 × 10 −6 , 3 × 10 −6 and 10 −5 respectively.