Sub-Coulomb transfer in collisions

Fission in238U+238U collisions below the Coulomb barrier

“…The dependence of the transfer probability on the distance of closest approach is expected to give some information on the excitation energy at which the nucleon transfer occurs. The experimental slope 2e= 1.07 _+0.01 fm -~ [10] was found to be very close to the calculated value 2 c~ = 1.03 fm -~ from the average neutron ground-state binding energies [18] thus indicating low excitation energies in the transfer products and therefore small fission probabilities after transfer, Coulomb excitation not yet taken into account. On the other hand, in the similar reaction i84W-q-z38u it was found, that most of the transfer fission observed occurs because of the simultaneous Coulomb excitation which takes place for these heavy ions [19].…”

“…1. The a39U counting was done for absolute normalization to avoid systematic errors in the comparison of the fission cross sections from this work with the separate measurements of one-neutron transfer in [10]. The fission cross sections are shown in Fig.…”

“…Dynamical alignment by the strong Coulomb forces in very heavy deformed collision systems may favour some relative orientations of the deformed nuclei at the distance of closest approach [21] and can influence the probability for a certain density overlap. Pure Coulomb fission induced by the longrange Coulomb forces as well as one-neutron transfer, which was shown to have only a weak dependence on the distance of closest approach and which was still observed at very large distances [10], cannot be taken as experimental signals for nuclear contact during the collision and do not probe small details of the nuclear potential. On the other hand, sequential fission after complex transfer reactions may indicate the formation of a window or a neck during the collision.…”

“…Recently we have reported on the excita-tion function and angular distributions for the oneneutron transfer product 239U [10]. Large deviations from semiclassical expectations, deformation not yet included, were seen for central collisions.…”

“…Angular distributions of the one-neutron transfer product 239U in the system 238U+/38U. The experimental data points and the semiclassical calculations (solid lines) are taken from [10]. The dashed lines are cross sections for sequential fission of 239U calculated from (1) …”