R.G. Stokstad

Coherent and incoherent processes in projectile breakup

Abstract We have studied the breakup of 140 MeV 16 O into 12 C + α by targets of 12 C, 13 C and 28 Si. At least two mechanisms contribute. One can be identified as the coherent excitation of the 16 O projectile to components of the giant resonance states. Another dominant mechanism may be the quasi-free scattering of the α or 12 C constituents of the projectile by the target.

Fusion of 16O + 144Sm at sub-barrier energies

Abstract Fusion cross sections have been measured for the system 16 O+ 144 Sm at bombarding energies in the range 63 MeV ⩽E lab ( 16 O )⩽72 MeV by observation of delayed X-rays emitted by the evaporation residues. Comparison of the present results for the magic nucleus 144 Sm with those already existing for the fusion of 16 O with other samarium isotopes shows that the enhancement of the cross sections at sub-barrier energies can be explained in terms of a one-dimensional barrier-penetration model that incorporates the quadrupole deformation parameter, s 2 . There is no need to invoke the neck degree of freedom.

Where has all the fusion gone

Abstract Charge distributions, kinetic energy spectra, and angular distributions were measured for the reverse kinematics reactions, 19.7 MeV/nucleon 40 Ar+ 12 C, 27 Al. Invariant cross section plots constructed in the V∥-V⊥ plane give a global view of the several competing reaction mechanisms. The evaporation residue cross section, which dominates the fusion cross section for the 40 Ar+ 12 C reaction, decreases dramatically in the 40 Ar+ 27 Al reaction and is replaced by isotropic binary decay, arising presumably from compound nucleus decay.

12C decay of 24Mg following nuclear inelastic scattering

Abstract The decay of 24Mg into two ground-state 12C nuclei following inelastic scattering of 15 MeV/nucleon 24Mg by a 12C target was studied. Three states at excitation energies in 24Mg of 21.9, 23.6 and 24.8 MeV were observed. Their spins, Jπ=2+ and, most likely, 0+ (2+) and 0+, respectively, have been inferred from the 12C12C angular correlations.

PARTITION OF EXCITATION ENERGY IN PERIPHERAL HEAVY-ION REACTIONS

Abstract The partition of excitation energy between target-like and projectile-like primary fragments from 11 MeV/nucleon 20 Ne + 197 Au quasi-elastic reactions was determined from kinematic analyses of three-body final states. Projectile breakup following stripping, pickup, and inelastic scattering was studied, and the excitation-energy partition was found to be strongly correlated with the direction of the mass transfer. Results are in quantitative agreement with optimum- Q -value calculations.

Momentum balance for the incomplete fusion of 16O+40Ca.

The velocities of fusion-like residues produced at 15/sup 0/ in the reaction 313 MeV /sup 16/O+/sup 40/Ca have been measured in coincidence with alpha particles emitted over a wide range of angles. The maximum of the residue velocity distribution depends on the energy and angle of emission of the alpha particle. Analysis of this dependence indicates that a significant portion of the fast alpha particles at forward angles results from the fusion of /sup 8/Be and the associated production of a /sup 8/Be ejectile.