R. Legrain

Spallation neutron production by 0.8, 1.2, and 1.6 GeV protons on various targets

Spallation neutron production in proton induced reactions on Al, Fe, Zr, W, Pb and Th targets at 1.2 GeV and on Fe and Pb at 0.8, and 1.6 GeV measured at the SATURNE accelerator in Saclay is reported. The experimental double-differential cross-sections are compared with calculations performed with different intra-nuclear cascade models implemented in high energy transport codes. The broad angular coverage also allowed the determination of average neutron multiplicities above 2 MeV. Deficiencies in some of the models commonly used for applications are pointed out.

A hot expanding source in 50 A MeV Xe+Sn central reactions

The INDRA multidetector has been used to study multifragmentation processes in central collisions for the Xe + Sn reaction at 50 A MeV. A single isotropic source formed at an excitation energy of 12 A MeV exhausting most of the emitted charged products has been isolated in such collisions. The fragment kinetic energy spectra indicate a fast disintegration of the system with a radial collective motion of about 2 A MeV. The light charged particle characteristics within this scenario are also discussed.

Measurement of isotopic cross-sections of spallation residues in 800-A/MeV Au-197 + p collisions

Abstract The spallation of 197 Au by 800 MeV protons was investigated in inverse kinematics at GSI, Darmstadt, by use of a 197 Au beam bombarding a liquid-hydrogen target. The fragment separator (FRS) was used to select and identify the reaction products prior to β decay. The individual production cross sections and the kinematic properties of 380 isotopes for all elements between mercury ( Z=80 ) and neodymium ( Z=60 ) have been measured. A comparison with a Monte-Carlo calculation based on the two-step model of the spallation reaction is given. The isotopic cross-section distribution of iridium isotopes is compared to that resulting from the aluminium-induced fragmentation of 197 Au. The mean kinetic energies of the fragments are deduced from the experimental data. The importance of the new data to improve our understanding of the spallation mechanism is discussed.

Isotopic production cross sections of fission residues in 197Au-on-proton collisions at 800 A MeV

Abstract Interactions of 197Au projectiles at 800 A MeV with protons leading to fission are investigated. We measured the production cross sections and velocities of all fission residues which are fully identified in atomic and mass number by using the in-flight separator FRS at GSI. The new data are compared with earlier measurements of the characteristics of fission in similar reactions. Both the production cross sections and the recoil energies are relevant for a better understanding of spallation reactions.

Surveying the nuclear caloric curve

Abstract The 4π array INDRA was used to detect nearly all charged products emitted in Ar + Ni collisions between 52 and 95 MeV/u. The charge, mass and excitation energy E ∗ of the quasi-projectiles have been reconstructed event by event. Excitation energies up to 25 MeV per nucleon are reached. Apparent temperatures obtained from several double isotopic yield ratios Tr0 show different dependences upon E ∗ . T6Li7Li3Heα0 yields the highest values, as well as the high energy slopes Ts of the kinetic energy spectra. Two statistical models, sequential evaporation and gas in complete equilibrium, taking into account side feeding and discrete excited states population, show that the data can be explained by a steady increase of the initial temperature with excitation energy without evidence for a liquid-gas phase transition.

Central collisions in the argon induced fission of thorium in the transition energy regime

Abstract Angular correlations between fission fragments induced by an 40Ar bombardment of 232Th targets at four energies, 31, 35, 39 and 44 MeV/u, have been measured as well as the energies, velocities and masses of both fragments. The characteristics of peripheral collisions remain about constant in the range studied, whereas the component attributed to the central collisions which shows a saturation in linear momentum transfer at 180 MeV/c per incident nucleon, has a cross section decreasing with bombarding energy which is correlated to an increase of the excitation energy of the fissioning nuclei.

Evaporation residues produced in the spallation reaction 238U+p at 1 A GeV

The production of heavy nuclides from the spallation-evaporation reaction of 238U induced by 1 GeV protons was studied in inverse kinematics. The evaporation residues from tungsten to uranium were identified in-flight in mass and atomic number. Their production cross-sections and their momentum distributions were determined. The data are compared with empirical systematics. A comparison with previous results from the spallation of 208Pb and 197Au reveals the strong influence of fission in the spallation of 238U.

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

Characteristics of the primary fragments produced in central collisions of 129Xe + natSn from 32 to 50 AMeV 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 3 AMeV for beam energies 39 AMeV and above. The corresponding secondary evaporated LCP represent less than 40% of all produced particles and decreases down to 23% for 50 AMeV. 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 LCPs.

Measurement of nuclide cross-sections of spallation residues in 1-A-GeV U-238 + proton collisions

The production of heavy nuclides from the spallation-evaporation reaction of 238U induced by 1 GeV protons was studied in inverse kinematics. The evaporation residues from tungsten to uranium were identified in-flight in mass and atomic number. Their production cross-sections and their momentum distributions were determined. The data are compared with empirical systematics. A comparison with previous results from the spallation of 208Pb and 197Au reveals the strong influence of fission in the spallation of 238U.

Tonneau: a multidetector array for charged-particle and light-fragment 4π detection☆

Abstract The central part of the light-particle detection unit for the GANIL multidetector is a spherical (80 cm radius) shell of 2 mm thick NE 102A plastic scintillator. It spans the range of polar angles from θ = 30° − 150° and the azimuthal range θ = 0° − 360°, and it is segment into 72 individual Δθ = 60° and Δθ = 10° wide detection modules. Each module is viewed by a photomultiplier at each end which provide information on the particle impact position, atomic number Z and velocity. The performance of the modules was studied with an α-source and during several experiments with heavy-ion beams from 25 up to 85 MeV/amu.