Neutron multiplicity in deep inelastic collisions: 400 MeV Cu+Au system

We have detected in nine different positions of space the neutrons associated with the collision of ⁶³Cu on ¹⁹⁷Au at 400 MeV bombarding energy. The deep inelastic products were detected at two different angles: close to the grazing angle and 30° forwards of it. Their masses were measured using a time-of-flight technique. The neutrons were detected in coincidence with the fragments - the efficiency of the neutron detectors was measured relatively to a ²⁵²Cf source during beam time. The neutron threshold was set at 300 keV. Within an accuracy of 10% all the emitted neutrons are evaporated by the fully accellerated deep inelastic fragments. It is shown that the excitation energy is shared between the fragments in proportion to their masses and that the relaxation time for internal equilibration of the composite system is very short (～10^?22 s).