Evidence for cluster emission in fusion reactions between 48Ti and 45Sc at 16 MeV/u

The reaction mechanism in collisions between ⁴⁸Ti and ⁴⁵Sc at 16 MeV/u leading to evaporation-residue-like fusion products (ER) was investigated by measuring and analyzing the ER velocity distributions as a function of ER mass. As expected for this nearly symmetric system the average ER velocities were found to be very close to the center-of-mass velocity. From the widths of the velocity distributions, quantitatively expressed by the variances S_x² and S_z² perpendicular and parallel to the beam direction, information on the recoil momenta of the emitted particles can be obtained. The quantitative analysis yields strong evidence for an incomplete-fusion process during which several correlated or clustered particles are emitted. An estimate of the cluster mass leads to mass numbers ranging from 10 to 20 depending on the ER mass. This interpretation is consistent with the measured ER cross section exceeding the value derived from the stability limit of the compound nucleus by a factor of two.