B. Mustapha

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.

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.

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.

Evaporation residues produced in spallation of Pb-208 by protons at 500-A-MeV

Abstract The production cross sections of fragmentation–evaporation residues in the reaction Pb + p at 500 A MeV have been measured using the inverse-kinematics method and the FRS spectrometer (GSI). Fragments were identified in nuclear charge using ionisation chambers. The mass identification was performed event-by-event using the B ρ – TOF – Δ E technique. Although partially-unresolved ionic charge states induced an ambiguity on the mass of some heavy fragments, production rates could be obtained with a high accuracy by systematically accounting for the polluting ionic charge states. The contribution of multiple reactions in the target was subtracted using a new, partly self-consistent code. The isobaric distributions are found to have a shape very close to the one observed in experiments at higher energy. Kinematic properties of the fragments were also measured. The total and the isotopic cross sections, including charge-pickup cross sections, are in good agreement with previous measurements and models. The data are discussed in the light of previous spallation measurements, especially on lead at 1 GeV.

Fission investigations in Au+p collisions at 800 A MeV

Fission induced by 197 Au on proton collisions is investigated in order to study the nuclear viscosity in highly excited nuclear matter. The isotopic identification of the fission residues allows to determine the mean values of the mass number, nuclear charge and excitation energy of the fissioning nuclei at saddle. The comparison of these properties with statistical fission calculations evidences the role of the nuclear viscosity in the description of the fission dynamics.