Spallation reactions studied with 4 pi-detector arrays

Recently there has been a renewed interest in the study of spallation react ions in basic nuclear physics as well as in potential applications. Spallat ion reactions induced by light projectiles (protons, antiprotons, pions, et c.) in the GeV range allow the formation of hot nuclei which do not suffer the collective excitations (compression, rotation, deformation) unavoidable when using massive projectiles. Such nuclei provide an ideal testbench for probing their decay as a function of excitation energy. In these investiga tions, 4 pi -detector arrays for charged particles and neutrons play a majo r role in the event-by-event sorting according to the excitation energy of the nucleus. Spallation reactions induced on heavy nuclei allow the conversion of the in cident GeV proton into several tens of evaporated neutrons. The neutron pro duction in thick targets has been investigated in great detail thanks to th e use of high efficiency neutron detector arrays. When scattered on samples of inert or biological materials, these neutrons can be used to study deta ils of the material structure. They could also be utilized for the transmut ation of long-lived nuclear wastes or for the feeding of sub-critical nucle ar reactors. The role of different types of multi-detector arrays is highlighted in this paper. Several references are also given for different uses of high effici ency neutron detectors in other contexts.