Inclusive neutron spectra at 0°from Nb-Nb and Au-Au collisions at 800 MeV/nucleon

Inclusive neutron spectra were measured at 0/sup 0/ from Nb-Nb and Au-Au collisions at 800 MeV/nucleon. The spectra in the rest frame of the projectile were decomposed into three Gaussians with standard deviations of 55 +- 4, 114 +- 12, and 259 +- 22 MeV/c for Nb-Nb collisions, and 56 +- 4, 110 +- 10, and 279 +- 15 MeV/c for Au-Au collisions. Physical processes associated with each Gaussian are discussed. The dependence of the parameters of the three Gaussians on the impact parameter indicates that the temperature of the spectators excited by peripheral collisions is lower than that excited by nonperipheral collisions, that projectile neutrons involved in nonperipheral collisions have a broader momentum distribution than those involved in peripheral collisions, and that an observed high-energy tail has its origin primarily in nonperipheral collisions. The high-energy tail is explained well by collective backscattering of neutrons in the target from nucleon clusters in the projectile with a mean cluster size of about 1.3 in both Nb and Au.