J.D. Bierman, P. Chan, M.P. Kelly, J.F. Liang, A.A. Sonzogni and R. Vandenbosch

Our experiment to determine the distributions of fusion barriers for the systems ⁴⁰Ca + ¹⁹²Os,¹⁹⁴Pt has been completed. The results have just recently been published.¹ In the Letter, coupled channel calculations were presented explaining which nuclear characteristics, oblate vs. prolate static quadrupole deformation, and couplings, projectile octupole and positive Q-value 2n transfer channels, were responsible for the structure present in the experimental results. While the calculations qualitatively agreed with the experimentally determined barrier distribution shapes, the calculations significantly overpredicted fusion at energies above the barrier and underpredicted fusion at energies below the barrier. We have since performed more coupled channel calculations attempting to improve agreement with the cross section data.

The new calculations include two significant modifications from those in the published letter. We have added a second transfer channel, 2n transfer from target to the first excited state in the projectile, the Q-value of which is still quite positive and of comparable coupling strength to transfer to the ground state. A second modification was to increase the nuclear diffuseness by approximately 35% over the default value. The need for a larger diffuseness has been noted in previous studies of barrier distributions.² The combination of these two changes results in calculations which are in much better agreement with the experimental results. The agreement with the barrier distributions is improved and the calculated fusion cross sections agree with the data far better than the previous results at energies both above and below the barrier region.

Fig. 3.3-1. Fusion cross sections and barrier distributions from both experimental work, data points, and coupled channels calculations for the systems ⁴⁰Ca + ¹⁹⁴Pt,¹⁹²Os. The left-hand panels are the platinum system results, osmium results are on the right. The full curve represents calculations including the deformations and couplings mentioned in the text. The dashed curve ignores these effects.