Fragments with $1<~Z<~12$, some with energies as low as 3 MeV/nucleon and some with energies as high as 120 MeV/nucleon, have been analyzed in high-energy nucleus-nucleus reactions with C, Ne, and Ar projectiles. For a given projectile the invariant cross sections of all fragments appear to define a "universal" curve that is exponential in momentum, provided momentum is evaluated in a frame in which the distribution is isotropic. The low speed of the frame (∼0.01c to ∼0.1c) suggests emission from the recoiling target.

• Received 31 May 1977

DOI:https://doi.org/10.1103/PhysRevLett.39.177