Rachel D Butt

Fusion versus breakup: observation of large fusion suppression for 9Be + 208Pb

Complete fusion excitation functions for

Absence of fusion suppression due to breakup in the 12C + 7Li reaction

{}^{9}\mathrm{Be}{+}^{208}\mathrm{Pb}

Influence of higher-order deformations in the 34 S + 168 Er fusion reaction

have been measured to high precision at near barrier energies. The experimental fusion barrier distribution extracted from these data allows reliable prediction of the expected complete fusion cross sections. However, the measured cross sections are only 68% of those predicted. The large cross sections observed for incomplete fusion products support the interpretation that this suppression of fusion is caused by

Insights into nuclear reactions through fusion barrier distribution measurements

{}^{9}\mathrm{Be}

Inhibition of Fusion in Mass-Asymmetric Collisions

breaking up into charged fragments before reaching the fusion barrier. Implications for the fusion of radioactive nuclei are discussed.

Memory of entrance-channel deformation for fast-fission

Abstract The fusion cross-section for 12C + 7Li has been determined, using a 12 C beam, at an energy near the Coulomb barrier. Previous measurements showed a large discrepancy in cross-sections, leading to conflicting conclusions regarding fusion suppression due to breakup. The present work resolves this discrepancy, and shows that there is no significant inhibition of fusion near the barrier.

Effect of Breakup on the Fusion of 6 Li, 7 Li and 9 Be with Heavy Nuclei

The shape of the measured barrier distribution for the ^{34}S + ^{168}Er reaction is analysed using the coupled-channels description. The ^{168}Er nucleus is a good candidate to test current fusion models description of deformation since it has a large quadrupole deformation with an insignificant hexadecapole deformation. Coupling to weaker channels, the 2^+_1 state in ^{34}S, the 3^-_1 state in ^{168}Er, and the pair neutron transfer channel, all were found to have little influence on the barrier distribution. A successful description of the barrier distribution was only obtained after the hexacontatetrapole deformation term in ^{168}Er (beta_6) was included in the coupling scheme. However, a positive value for beta_6 was needed where the macroscopic-microscopic model predicts a negative one.

Fusion and Breakup in the Reactions of 6 Li and 7 Li Nuclei with 209 Bi

The study of nuclear fusion has been greatly enhanced following the realisation that an experimental fusion barrier distribution can be determined from precisely measured fusion cross-sections. Experimental fusion barrier distributions for different reactions have shown clear signatures of a range of nuclear structure effects, for example those of static quadrupole and hexadecapole deformations, and of coupling to single- and double-phonon states. Applications of this improved quantitative understanding of fusion in the fields of fission, and fusion of weakly bound nuclei are discussed.

Unexpected inhibition of fusion in nucleus-nucleus collisions.

Comprehensive fission and evaporation residue measurements have been made for three reactions, all of which lead to the 216Ra compound nucleus, at energies from the Coulomb barriers upwards. The results show inhibition of fusion and the increasing presence of quasi-fission with decreasing mass-asymmetry of the projectile and target combination in the entrance channel. This work demonstrates a lower threshold for the inhibition of fusion and the onset of quasi-fission than previously expected.

Systematic failure of the Woods-Saxon nuclear potential to describe both fusion and elastic scattering: Possible need for a new dynamical approach to fusion

Abstract Fission fragment anisotropies following fusion of 34 S with 168 Er have been measured for energies at which a substantial fraction of fission results from angular momenta where the fission barrier height is less than the temperature. Here, transition state model calculations were found to be larger than the measured anisotropies. This result contrasts with data for 19 F+ 208 Pb, where the transition state model underestimated the measured anisotropies. Both observations can be explained qualitatively assuming that high angular momentum events fission with some memory of the entrance-channel K -distribution, which is narrow for the spherical 208 Pb target nucleus, and broad for the deformed 168 Er.