M.F. Rivet

Bio: M.F. Rivet is an academic researcher from Centre national de la recherche scientifique. The author has contributed to research in topics: Nucleon & Nuclear reaction. The author has an hindex of 36, co-authored 156 publications receiving 3134 citations.

INDRA, a 4π charged product detection array at GANIL

Abstract: INDRA, a new and innovative highly segmented detector for light charged particles and fragments is described. It covers geometrically 90% of the 4π solid angle and has very low detection thresholds. The detector, operated under vacuum, is axially symmetric and segmented in 336 independent cells allowing efficient detection of high multiplicity events. Nucleus identification down to very low energy threshold (≈ 1 A MeV) is achieved by using ionization chambers operated with low pressure C 3 F 8 gas. Residual energies are measured by a combination of silicon (300 μm thick) and cesium iodide (5 to 14 cm in length) detectors. Very forward angles are covered by fast counting phoswich scintillators (NE102/NE115). Charge resolution up to Z = 50 is achieved on a large energy dynamic range (5000 to 1 for silicon detectors). Isotopic separation is obtained up to Z = 3. The treatment of the signals is performed through specifically designed and highly integrated modules, most of which are in the new VXIbus standard. Full remote control of parameter settings, including visualization of signals, is thus allowed. The detector is continuously monitored with a laser source and electronic pulsers and is found stable over several days. Energy calibration procedures, making use of specific detectors and the ability of the GANIL accelerator to deliver secondary beams, have been developed. First experiments were performed in the spring of 1993.

Dynamical effects and intermediate mass fragment production in peripheral and semicentral collisions of Xe+Sn at 50 MeV/nucleon

Abstract: Experimental data obtained with the 4{pi} multidetector system INDRA are used to study the light charged particle (LCP, Z{le}2) and intermediate mass fragment (IMF, Z{ge}3) production in peripheral and semicentral collisions of Xe and Sn at 50 MeV/nucleon. It is found that a sizable fraction of the detected LCP`s and IMF`s originates from the midvelocity region. These fragments can be seen to come either from a prompt (preequilibrium) mechanism or from a slower but dynamically influenced emission process. The relative magnitude of the dynamically influenced emission relative to the isotropic statistical evaporation is presented as a function of the transverse energy of light particles, used as an impact parameter selector. The results are compared to dynamical models with which a good agreement is obtained. {copyright} {ital 1997} {ital The American Physical Society}

Characteristics of the fragments produced in central collisions of129Xe+natSnfrom 32Ato 50AMeV

Abstract: Characteristics of the primary fragments produced in central collisions of ${}^{129}\mathrm{Xe}{+}^{\mathrm{nat}}\mathrm{Sn}$ from 32 to 50 A MeV have been obtained. By using the correlation technique for the relative velocity between light charged particles (LCP) and fragments, we were able to extract the multiplicities and average kinetic energy of secondary evaporated LCP. We then reconstructed the size and excitation energy of the primary fragments. For each bombarding energy a constant value of the excitation energy per nucleon over the whole range of fragment charge has been found. This value saturates at 3A MeV for beam energies 39A MeV and above. The corresponding secondary evaporated LCP represent less than 40% of all produced particles and decreases down to 23% for 50A MeV. The experimental characteristics of the primary fragments are compared to the predictions of statistical multifragmentation model (SMM) calculations. Reasonable agreement between the data and the calculation has been found for any given incident energy. However SMM fails to reproduce the trend of the excitation function of the primary fragment excitation energy and the amount of secondary evaporated LCP's.

Nucleosynthesis in massive stars with improved nuclear and stellar physics

Abstract: We present the first calculations to follow the evolution of all stable nuclei and their radioactive progeni- tors in stellar models computed from the onset of central hydrogen burning through explosion as Type II supernovae. Calculations are performed for Population I stars of 15, 19, 20, 21, and 25 Musing the most recently available experimental and theoretical nuclear data, revised opacity tables, neutrino losses, and weak interaction rates and taking into account mass loss due to stellar winds. A novel '' adaptive '' reaction net- work is employed with a variable number of nuclei (adjusted each time step) ranging from � 700 on the main sequence to e2200 during the explosion. The network includes, at any given time, all relevant isotopes from hydrogen through polonium (Z ¼ 84). Even the limited grid of stellar masses studied suggests that overall good agreement can be achieved with the solar abundances of nuclei between 16 O and 90 Zr. Interesting dis- crepancies are seen in the 20 Mmodel and (so far, only in that model) are a consequence of the merging of the oxygen, neon, and carbon shells about a day prior to core collapse. We find that, in some stars, most of the '' p-process '' nuclei can be produced in the convective oxygen-burning shell moments prior to collapse; in others, they are made only in the explosion. Serious deficiencies still exist in all cases for the p-process isotopes of Ru and Mo. Subject headings: nuclear reactions, nucleosynthesis, abundances — stars: evolution — supernovae: general On-line material: machine-readable tables

General relativistic boson stars

Abstract: There is accumulating evidence that (fundamental) scalar fields may exist in nature. The gravitational collapse of such a boson cloud would lead to a boson star (BS) as a new type of a compact object. As with white dwarfs and neutron stars, a limiting mass exists similarly, below which a BS is stable against complete gravitational collapse to a black hole. According to the form of the self-interaction of the basic constituents and spacetime symmetry, we can distinguish mini-, axidilaton, soliton, charged, oscillating and rotating BSs. Their compactness prevents a Newtonian approximation; however, modifications of general relativity, as in the case of Jordan?Brans?Dicke theory as a low-energy limit of strings, would provide them with gravitational memory. In general, a BS is a compact, completely regular configuration with structured layers due to the anisotropy of scalar matter, an exponentially decreasing 'halo', a critical mass inversely proportional to the constituent mass, an effective radius and a large particle number. Due to the Heisenberg principle, a completely stable branch exists, and as a coherent state, it allows for rotating solutions with quantized angular momentum. In this review, we concentrate on the fascinating possibilities of detecting the various subtypes of (excited) BSs: possible signals include gravitational redshift and (micro-)lensing, emission of gravitational waves, or, in the case of a giant BS, its dark matter contribution to the rotation curves of galactic halos.