Particle-particle correlations: Independent particle emission versus sequential decay of heavy fragments

Particle-particle coincidence measurements for both large and small separation angles are reported for the reactions 140 MeV ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{27}$Al→p-p, p-d, d-d, α-α, d-α, and p-α. Two clusters of seven detectors were used at ±50°, on both the right and left sides of the beam axis. Coincidence data were compared for nearest-neighbor and across-beam geometries. For p-p, p-d, and d-d pairs, the results of this symmetry test are consistent with independent particle evaporation. For the α-α, d-α, p-α pairs, the results indicate significant contributions from breakup of preformed fragments. These results suggest that small-angle correlations for the former pairs are useful as probes of the space-time extent of the emitters, but that the latter pairs are compromised for this task.