New generation of measurements and model developments on nuclide production in spallation reactions

Abstract

With its powerful installations, GSI, Darmstadt, provides unique conditions for fundamental and applied research on a variety of subjects in nuclear physics and other fields with heavy-ion beams of stable and radioactive species. Intensive work on nuclear data is being made, e.g., on nuclear masses, half lives, nuclide yields from low- energy fission, and nuclide production in spallation reactions. The interest in spallation reactions with primary proton energies around 1GeV is motivated by the accelerator-driven system, dedicated to the incineration of nuclear waste. An innovative experimental method has been developed, based on inverse kinematics, which allowed for the first time to identify all reaction residues in-flight, using the high-resolution magnetic spectrometer FRS, and thus to determine full nuclide distributions. It also gives direct access to the reaction kinematics. During the last years, an experimental campaign has been carried out in a Europe-wide collaboration, investigating the spallation of several nuclei ranging from 56 Fe to 238 U. Complementary experiments were performed with a full-acceptance detection system, yielding total fission cross sections with high precision. Recently, another detection system using the large- acceptance ALADIN dipole and the LAND neutron detector was introduced to measure light particles in coincidence with the heavy residues. Another intense activity was dedicated to develop codes which cover the nuclear reactions occurring in an ADS in their full energy range and in all target materials involved. Most effort was invested in modelling the later de-excitation stage of the reaction, which is responsible for the salient features observed in the residual nuclide distributions due to the different possible de-excitation paths like evaporation of nucleons, light charged particles and intermediate-mass fragments, fission and multi-fragmentation. The future FAIR facility will provide primary beams with higher intensities and higher energies, a considerably extended variety of secondary beams, and a number of new installations, e.g., powerful magnetic spectrometers, storage rings and colliders. A new generation of experiments on fission-fragment yields with tagged photons using secondary beams is described as an example for future developments.